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EK-VT420-RM-002

November 1992

378 pages

Original

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Document:	VT420 Programmer Reference Manual
Order Number:	EK-VT420-RM
Revision:	002
Pages:	378
Original Filename:

OCR Text

VT420 Programmer
Reference Manual
Order Number EK–VT420–RM.002

Digital Equipment Corporation

First Edition, November 1989
Second Edition, February 1992
The information in this document is subject to change without notice and should not
be construed as a commitment by Digital Equipment Corporation. Digital Equipment
Corporation assumes no responsibility for any errors that may appear in this document.
The software described in this document is furnished under a license and may be used or
copied only in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment that is not
supplied by Digital Equipment Corporation or its affiliated companies.
Restricted Rights: Use, duplication, or disclosure by the U. S. Government is subject to
restrictions as set forth in subparagraph ( c ) ( 1 ) ( ii ) of the Rights in Technical Data and
Computer Software clause at DFARS 252.227–7013.
Copyright © Digital Equipment Corporation 1989, 1992
All Rights Reserved.
Printed in U.S.A.
The following are trademarks of Digital Equipment Corporation: DEC, DEClaser, DECnet,
DECserver, LA, LA50, LA75 Companion, LA324, LN01, LN03, LQP02, Scholar, SSU, VMS,
VT, VT52, VT100, VT220, VT320, and VT420.
AT&T is a registered trademark of American Telephone and Telegraph Company.
IBM is a registered trademark of International Business Machines Corporation.
This document was prepared and published by Educational Services Development and
Publishing, Digital Equipment Corporation.

Contents
About This Manual
Part 1

xvii

Introduction to Your
VT420 Terminal

VT420 Features

VT420 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
New Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PC TERM Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Two Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
User Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Macro Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rectangular Area Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Local Copy and Paste Feature (VT Mode) . . . . . . . . . . . . . . . . . .
Number of Lines/Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Set-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Text Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Communication Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4
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12

iii

iv Contents

Character Encoding

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Coding Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Characters and Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Code Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7-Bit ASCII Code Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-Bit Code Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VT420 Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DEC Supplemental Graphic Character Set . . . . . . . . . . . . . . . . .
ISO Latin Alphabet Nr 1 Supplemental Character Set . . . . . . . .
National Replacement Character Sets (NRC Sets)
(Worldwide Models Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DEC Special Graphic Character Set . . . . . . . . . . . . . . . . . . . . . . .
DEC Technical Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Downloaded (Soft) Character Set . . . . . . . . . . . . . . . . . . . . . . . . .
Control Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sequence Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Escape Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Numeric Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selective Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Device Control Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Control Characters in Sequences . . . . . . . . . . . . . . . . . . . .
7-Bit Code Extension Technique . . . . . . . . . . . . . . . . . . . . . . . . . .
Working with 7-Bit and 8-Bit Environments . . . . . . . . . . . . . . . . . .
Conventions for Codes Received by the Terminal . . . . . . . . . . . . .
Conventions for Codes Sent by the Terminal . . . . . . . . . . . . . . . .
Using Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Define Macro (DECDMAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Invoke Macro (DECINVM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Controls Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents v

Part 2

Control Functions
Sent to the Host

ANSI, Short ANSI, and PC Keyboard Codes

Keyboard Layouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Standard Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special-Function Keys (ANSI Keyboard) . . . . . . . . . . . . . . . . . . .
Special-Function Keys (Short ANSI Keyboard) . . . . . . . . . . . . . .
Special-Function Keys (PC Keyboard) . . . . . . . . . . . . . . . . . . . . .
Editing Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Numeric Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Top-Row Function Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7-Bit Control Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turning Autorepeat On and Off . . . . . . . . . . . . . . . . . . . . . . . . . .
Unlocking the Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part 3

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Control Functions
Received from the Host

Emulating VT Series Terminals

Level 1 (VT100 Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Level 4 (VT400 Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
All Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selecting an Operating Level (DECSCL) . . . . . . . . . . . . . . . . . .
Sending C1 Controls to the Host . . . . . . . . . . . . . . . . . . . . . . . . .
National Replacement Character Set Mode (DECNRCM) . . . . . .

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vi Contents

Using Character Sets

Selecting Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Designating Character Sets (SCS Sequences) . . . . . . . . . . . . . . .
Mapping Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Locking Shifts (LS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Single Shifts (SS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
National Replacement Character Sets
(Worldwide Model Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Assigning User-Preferred Supplemental Sets (DECAUPSS) . .
ANSI Conformance Levels . . . . . . . . . . . . . . . . . . . . . . . . . . .
Soft Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Designing a Soft Character Set . . . . . . . . . . . . . . . . . . . . . . . . . .
Coding the Soft Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . .
Downloading Soft Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Downline Load (DECDLD) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Designating the Soft Character Set . . . . . . . . . . . . . . . . . . . . . . .
Soft Character Set Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clearing a Soft Character Set . . . . . . . . . . . . . . . . . . . . . . . . . . .

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125

Page Memory

What is Page Memory? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Memory for One Session . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Memory for Two Sessions . . . . . . . . . . . . . . . . . . . . . . . . . .
Controlling the Page Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selecting 80 or 132 Columns per Page . . . . . . . . . . . . . . . . . . . .
Set Lines per Page (DECSLPP) . . . . . . . . . . . . . . . . . . . . . . . . .
Set Left and Right Margins (DECSLRM) . . . . . . . . . . . . . . . . . .
Set Top and Bottom Margins (DECSTBM) . . . . . . . . . . . . . . . . .
Origin Mode (DECOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vertical Split Screen Mode (DECVSSM) . . . . . . . . . . . . . . . . . . .
Moving to Another Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Next Page (NP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preceding Page (PP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Position Absolute (PPA) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Position Backward (PPB) . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Position Relative (PPR) . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents vii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Setting Visual Character and Line Attributes

Setting Visual Character Attributes . . . . . . . . . . . . . . . . . . . . . . . . .
Select Graphic Rendition (SGR) . . . . . . . . . . . . . . . . . . . . . . . . .
Setting Line Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Single-Width, Single-Height Line (DECSWL) . . . . . . . . . . . . . . .
Double-Width, Single-Height Line (DECDWL) . . . . . . . . . . . . . .
Double-Width, Double-Height Line (DECDHL) . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Editing

Inserting and Deleting Columns, Lines, and Characters . . . . . . . . .
Insert/Replace Mode (IRM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Delete Column (DECDC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Insert Column (DECIC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Delete Line (DL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Insert Line (IL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Delete Character (DCH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Insert Character (ICH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Erasing Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Erase in Display (ED) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Erase in Line (EL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Erase Character (ECH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selectively Erasing Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Select Character Protection Attribute (DECSCA) . . . . . . . . . . . .
Selective Erase in Display (DECSED) . . . . . . . . . . . . . . . . . . . . .
Selective Erase in Line (DECSEL) . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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viii Contents

Rectangular Area Operations

Copying, Filling, and Erasing Rectangular Areas . . . . . . . . . . . . . .
Copy Rectangular Area (DECCRA) . . . . . . . . . . . . . . . . . . . . . . .
Fill Rectangular Area (DECFRA) . . . . . . . . . . . . . . . . . . . . . . . .
Erase Rectangular Area (DECERA) . . . . . . . . . . . . . . . . . . . . . .
Selective Erase Rectangular Area (DECSERA) . . . . . . . . . . . . . .
Changing Attributes of Rectangles . . . . . . . . . . . . . . . . . . . . . . . . . .
Select Attribute Change Extent (DECSACE) . . . . . . . . . . . . . . .
Change Attributes in Rectangular Area (DECCARA) . . . . . . . . .
Reverse Attributes in Rectangular Area (DECRARA) . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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172

Cursor Movement and Panning

The Cursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Text Cursor Enable Mode (DECTCEM) . . . . . . . . . . . . . . . . . . . .
Moving the Cursor on the Current Page . . . . . . . . . . . . . . . . . . . . .
Back Index (DECBI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forward Index (DECFI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Position (CUP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Horizontal and Vertical Position (HVP) . . . . . . . . . . . . . . . . . . . .
Cursor Forward (CUF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Backward (CUB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Up (CUU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Down (CUD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Panning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pan Down (SU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pan Up (SD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vertical Cursor-Coupling Mode (DECVCCM) . . . . . . . . . . . . . . .
Page Cursor-Coupling Mode (DECPCCM) . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents ix

Keyboard, Printing, and Display Commands

Keyboard Control Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Action Mode (KAM) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Backarrow Key Mode (DECBKM) . . . . . . . . . . . . . . . . . . . . . . . .
Line Feed/New Line Mode (LNM) . . . . . . . . . . . . . . . . . . . . . . . .
Autorepeat Mode (DECARM) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Autowrap Mode (DECAWM) . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Keys Mode (DECCKM) . . . . . . . . . . . . . . . . . . . . . . . . . .
Numeric Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keypad Application and Numeric Modes (DECKPAM and
DECKPNM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Numeric Keypad Mode (DECNKM) . . . . . . . . . . . . . . . . . .
Typewriter or Data Processing Keys . . . . . . . . . . . . . . . . . . . .
Key Position Mode (DECKPM) . . . . . . . . . . . . . . . . . . . . . . . .
Enable Local Functions (DECELF) . . . . . . . . . . . . . . . . . . . . .
Local Function Key Control (DECLFKC) . . . . . . . . . . . . . . . .
Select Modifier Key Reporting (DECSMKR) . . . . . . . . . . . . . .
Extended Keyboard Report (DECEKBD) . . . . . . . . . . . . . . . .
User-Defined Keys (DECUDK) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using UDKs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
UDK Memory Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Programming UDKs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printer Port Control Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printer Extent Mode (DECPEX) . . . . . . . . . . . . . . . . . . . . . . . . .
Print Form Feed Mode (DECPFF) . . . . . . . . . . . . . . . . . . . . . . .
Printing Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printing a Display Line: Autoprint Mode . . . . . . . . . . . . . . . . . .
Sending Characters Directly to the Printer:
Printer Controller Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Print Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Print Composed Main Display . . . . . . . . . . . . . . . . . . . . . . . . . .
Print All Pages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Print Cursor Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Start Printer-to-Host Session . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stop Printer-to-Host Session . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Assign Printer to Active Host Session . . . . . . . . . . . . . . . . . . . . .

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214
214

x Contents

Release Printer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printing Visual Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sending Line Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sending Visual Character Attributes . . . . . . . . . . . . . . . . . . . . . .
Screen Display Control Functions . . . . . . . . . . . . . . . . . . . . . . . . . .
Local Echo: Send/Receive Mode (SRM) . . . . . . . . . . . . . . . . . . . .
Light or Dark Screen: Screen Mode (DECSCNM) . . . . . . . . . . . .
Scrolling Mode (DECSCLM) . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Select Number of Lines/Screen (DECSNLS) . . . . . . . . . . . . . . . .
Selecting the Indicator or Host-Writable Status Line . . . . . . . . . .
Select Active Status Display (DECSASD) . . . . . . . . . . . . . . . .
Select Status Line Type (DECSSDT) . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

214
214
215
215
215
216
216
217
218
219
219
220
222

VT420 Reports

Device Attributes (DA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Primary DA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Secondary DA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tertiary DA (VT400 Mode Only) . . . . . . . . . . . . . . . . . . . . . . . . .
Terminal Identification (DECID) . . . . . . . . . . . . . . . . . . . . . . . . .
Device Status Report (DSR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—VT420 Operating Status . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—Cursor Position Report (CPR) . . . . . . . . . . . . . . . . . . . . . .
DSR—Extended Cursor Position Report (DECXCPR) . . . . . . . . .
DSR—Printer Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—User-Defined Keys (VT400 Mode Only) . . . . . . . . . . . . . .
DSR—Keyboard Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—Macro Space Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—Memory Checksum (DECCKSR) . . . . . . . . . . . . . . . . . . . .
DSR—Data Integrity Report . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—Multiple-Session Configuration Status Report . . . . . . . . .
Requesting a Checksum of a Rectangular Area . . . . . . . . . . . . . . . .
Request Checksum of Rectangular Area (DECRQCRA) (VT400
Mode Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checksum Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Terminal State Reports (VT400 Mode Only) . . . . . . . . . . . . . . . . . .

228
229
232
233
234
235
235
236
236
237
238
238
240
240
241
242
242
243
244
244

Contents xi

Request Terminal State Report (DECRQTSR)—Host To VT420 .
Terminal State Report (DECTSR)—VT420 to Host . . . . . . . . . . .
Restore Terminal State (DECRSTS)—VT400 Mode Only . . . . . .
Presentation State Reports (VT400 Mode Only) . . . . . . . . . . . . . . . .
Request Presentation State Report (DECRQPSR)
—Host to VT420 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cursor Information Report (DECCIR)—VT420 to Host . . . . . . . .
Tab Stop Report (DECTABSR)—VT420 To Host . . . . . . . . . . . . .
Restore Presentation State (DECRSPS)—VT400 Mode Only . . .
Mode Settings (VT400 Mode Only) . . . . . . . . . . . . . . . . . . . . . . . . . .
Request Mode (DECRQM)—Host To VT420 . . . . . . . . . . . . . . . .
Report Mode (DECRPM)—VT420 To Host . . . . . . . . . . . . . . . . .
Setting or Resetting Modes (SM and RM) . . . . . . . . . . . . . . . . . .
Set Mode (SM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset Mode (RM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Function Settings (VT400 Mode Only) . . . . . . . . . . . . . . . .
Request Selection or Setting (DECRQSS)—Host To VT420 . . . . .
Report Selection or Setting (DECRPSS)—VT420 To Host . . . . . .
Saving and Restoring the Cursor State . . . . . . . . . . . . . . . . . . . . . .
Save Cursor (DECSC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Restore Cursor (DECRC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Window Reports (VT400 Mode Only) . . . . . . . . . . . . . . . . . . . . . . . .
Request Displayed Extent (DECRQDE) . . . . . . . . . . . . . . . . . . .
Report Displayed Extent (DECRPDE) . . . . . . . . . . . . . . . . . . . . .
User-Preferred Supplemental Set (DECRQUPSS)—(VT400 Mode
Only) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

245
245
246
247
248
248
254
255
257
257
261
263
263
264
266
267
268
269
270
270
271
271
272
273
274

Resetting and Testing the Terminal

Resetting the Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Soft Terminal Reset (DECSTR) . . . . . . . . . . . . . . . . . . . . . . . . . .
Reset to Initial State (RIS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Secure Reset (DECSR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Secure Reset Confirmation (DECSRC) . . . . . . . . . . . . . . . . . . . .
Tab Clear (TBC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testing the Terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

284
285
286
288
289
290
291

xii Contents

Screen Alignment Pattern (DECALN) . . . . . . . . . . . . . . . . . . . . .
Invoke Confidence Test (DECTST)—Power-Up Self-Test . . . . . . .
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part 4
14

Session Management

Two Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Two Ways to Manage Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Session Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Independent Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Shared Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Multiple System Communications (MSC) . . . . . . . . . . . . . . . . . . . . .
SSU Software (VT Mode) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SSU Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ANSI/VT52 Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SSU Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
XON/XOFF Data Flow Control . . . . . . . . . . . . . . . . . . . . . . . .
Using SSU Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selecting Sessions (MSC or SSU Software) . . . . . . . . . . . . . . . . . . .
Enable Session Command . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Part 5
15

291
291
293

297
297
300
300
301
301
302
302
302
302
302
303
303
303

Emulating a Personal Computer

Operating in PC TERM Mode

How the VT420 Operates in PC TERM Mode . . . . . . . . . . . . . . . . .
Sequence of Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Codes Sent in PC TERM Mode . . . . . . . . . . . . . . . . . . . .
Enabling or Disabling PC TERM Mode . . . . . . . . . . . . . . . . . . . . . .
Change Emulation Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Enabling PC Keyboard Commands . . . . . . . . . . . . . . . . . . . . . . . . .
Data and Commands Sent from the Host to the Terminal . . . . . .
Secondary DA—PC Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DSR—PC Keyboard Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

307
308
309
310
311
312
313
313
313

Contents xiii

Using PC Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Selecting PC Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PC Keyboard Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Scan Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Key Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Standard Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Editing Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Numeric Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Top-Row Function Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

VT52 Mode Control Codes

VT52 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exiting VT52 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

313
318
318
318
318
319
319
322
324
325
326

327
328

Communication

Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Host System and Printer Port Interfaces . . . . . . . . . . . . . . . . . . . . .
Modems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Character Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Terminal-to-Host Data Flow Control . . . . . . . . . . . . . . . . . . . . . . . .
Using Fill Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transmit Rate Limiting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transmit Rate Limiting (DECXRLM) . . . . . . . . . . . . . . . . . . .
Modem Connections and Disconnections . . . . . . . . . . . . . . . . . . .
Terminal-to-Printer Data Flow Control . . . . . . . . . . . . . . . . . . . . . .
Using C1 Control Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . .

330
330
331
331
332
332
334
334
334
335
335
336

xiv Contents

Related Documentation

Compatibility with Other Digital Terminals

Glossary
Figures
1–1
2–1
2–2
2–3
2–4
2–5
2–6

VT420 Video Display Terminal with Keyboards . . . . . . . . . . .
VT Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7-Bit ASCII Code Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7-Bit Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-Bit Code Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-Bit Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DEC Multinational Character Set (Left Half—C0 and GL
Codes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–7 DEC Multinational Character Set (Right Half—C1 and GR
Codes) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2–8 ISO Latin Nr 1 Supplemental Character Set . . . . . . . . . . . . .
2–9 DEC Special Graphic Character Set . . . . . . . . . . . . . . . . . . . .
2–10 DEC Technical Character Set . . . . . . . . . . . . . . . . . . . . . . . . .
2–11 Display Controls Font (Left Half) . . . . . . . . . . . . . . . . . . . . . .
2–12 Display Controls Font (Right Half) . . . . . . . . . . . . . . . . . . . .
3–1 ANSI Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–2 Short ANSI Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3–3 PC Keyboard (North American/United Kingdom Keyboard) . .
3–4 Standard Key with a Data Processing Character
(French/Belgian ANSI Keyboard) . . . . . . . . . . . . . . . . . . . . . .
5–1 Character Set Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–2 Designating and Mapping Character Sets in VT400 Mode . . .
5–3 Designating and Mapping Character Sets in VT100 Mode . . .
5–4 Character Cell Sizes for 24-Line by 80- and 132-Column
Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–5 Character Body Sizes for 24-Line by 80- and 132-Column
Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5–6 Example of an Uppercase D (24-Line by 80-Column Font) . . .
5–7 Sixel-to-ASCII Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . .

5
14
18
19
21
22
24
25
26
29
30
52
53
58
59
60
62
92
96
97
103
105
108
112

Contents xv

6–1
6–2
6–3
10–1
14–1
14–2
15–1
15–2
15–3
15–4
15–5
15–6

A Page in Page Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Sizes for One Session . . . . . . . . . . . . . . . . . . . . . . . . . .
Page Sizes for Two Sessions . . . . . . . . . . . . . . . . . . . . . . . . . .
The Difference Between Scrolling and Panning . . . . . . . . . . .
Typical MSC Environments . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical SSU Environment . . . . . . . . . . . . . . . . . . . . . . . . . . .
PC TERM Mode Operation . . . . . . . . . . . . . . . . . . . . . . . . . .
PC International and PC Multilingual Character Sets (CO
and GL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PC International Character Set (C1 and GR) . . . . . . . . . . . . .
PC Multilingual Character Set (C1 and GR) . . . . . . . . . . . . .
North American PC Keyboard (101 Keys) . . . . . . . . . . . . . . .
Worldwide PC Keyboard (102 Keys) . . . . . . . . . . . . . . . . . . . .

127
128
129
175
298
299
308
314
315
316
320
321

Tables
2–1
2–2
2–3
2–4
2–5
3–1
3–2
3–3
3–4
3–5
3–6
3–7
4–1
5–1
5–2
5–3
5–4
5–5
5–6

National Replacement Character Sets . . . . . . . . . . . . . . . . . .
C0 (7-Bit) Control Characters Recognized . . . . . . . . . . . . . . .
C1 (8-Bit) Control Characters Recognized . . . . . . . . . . . . . . .
8-Bit Control Characters and Their 7-Bit Equivalents . . . . . .
Displaying Controls in 36 or 48 Lines . . . . . . . . . . . . . . . . . .
Codes Sent by Editing Keys (ANSI/Short ANSI Keyboards) .
Codes Sent by Editing Keys (PC Keyboard) . . . . . . . . . . . . . .
Codes Sent by Arrow Keys . . . . . . . . . . . . . . . . . . . . . . . . . . .
Codes Sent by Numeric Keypad Keys (ANSI, Short ANSI,
and PC Keyboards) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Codes Sent by Numeric Keypad Keys (PC Keyboard, PC Key
Layout) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Codes Sent by the Top-Row Function Keys . . . . . . . . . . . . . .
Keys Used to Send 7-Bit Control Characters . . . . . . . . . . . . .
Control Functions Ignored in Level 1 (VT100 mode) . . . . . . .
Character Sets Available . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Designating a Character Set . . . . . . . . . . . . . . . . . . . . . . . . .
Character Set Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mapping Character Sets with Locking Shifts . . . . . . . . . . . . .
Character Cell Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Guidelines for Designing Soft Characters . . . . . . . . . . . . . . .

28
31
33
35
49
65
65
66
67
71
73
78
84
90
93
94
98
104
106

xvi Contents

5–7
5–8
5–9
6–1
6–2
7–1
7–2
8–1
9–1
10–1
11–1
11–2
11–3
11–4
11–5
11–6
12–1
12–2
12–3
12–4
12–5
13–1
13–2
15–1
15–2
15–3
15–4
15–5
15–6
15–7
A–1

Converting Binary Code to an ASCII Character . . . . . . . . . .
DECDLD Parameter Characters . . . . . . . . . . . . . . . . . . . . . .
Valid DECDLD Parameter Combinations . . . . . . . . . . . . . . .
Page Format Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sequences for Moving Through Page Memory . . . . . . . . . . . .
Visual Character Attribute Values . . . . . . . . . . . . . . . . . . . . .
Visual Character and Line Attribute Sequences . . . . . . . . . .
Editing Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rectangular Area Control Functions . . . . . . . . . . . . . . . . . . .
Cursor Movement and Panning Sequences . . . . . . . . . . . . . .
ANSI and Short ANSI Keyboards . . . . . . . . . . . . . . . . . . . . .
PC Keyboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Keyboard Control Sequences . . . . . . . . . . . . . . . . . . . . . . . . .
Programming UDKs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Printing Control Sequences . . . . . . . . . . . . . . . . . . . . . . . . . .
Screen Display Control Sequences . . . . . . . . . . . . . . . . . . . . .
Alias Primary DA Responses From the VT420 . . . . . . . . . . . .
ANSI Modes for DECRQM, DECRPM, SM, and RM . . . . . . .
DEC Private Modes for DECRQM, DECRPM, SM, and RM . .
Control Functions for DECRQSS Requests . . . . . . . . . . . . . .
Sequences for VT420 Reports . . . . . . . . . . . . . . . . . . . . . . . . .
Soft Terminal Reset (DECSTR) States . . . . . . . . . . . . . . . . . .
VT420 Reset Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Control Codes for PC Character Sets . . . . . . . . . . . . . . . . . . .
PC Keyboard Commands in PC TERM Mode . . . . . . . . . . . . .
National PC Character Sets . . . . . . . . . . . . . . . . . . . . . . . . . .
Scan Codes Sent by Standard Keys . . . . . . . . . . . . . . . . . . . .
Scan Codes Sent by Editing and Arrow Keys . . . . . . . . . . . . .
Scan Codes Sent by Numeric Keypad Keys . . . . . . . . . . . . . .
Scan Codes Sent by Programmable Function Keys . . . . . . . .
VT52 Escape Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109
116
121
140
141
143
147
158
172
185
207
208
222
225
226
227
231
259
260
266
274
285
293
310
312
317
322
324
325
326
328

About This Manual

This reference manual is for people with a general knowledge of computer
programming. The manual provides programmers with information
needed in writing applications for the VT420 text terminal.
For general user information, see Installing and Using the VT420 Video
Terminal.

New Features in This Revision
This revised manual provides new information on operating a VT420 text
terminal in PC TERM mode.
There are several versions of the VT420 text terminal:
•

North American model—Operates in VT mode.

•

Worldwide model—Operates in VT mode.

•

Worldwide model with PC TERM mode—Operates in VT mode or PC
TERM mode.

xvii

xviii About This Manual

Organization
The manual is divided into five parts.
Part 1: Introduction to Your VT420 Terminal
Part 1 covers information you need to know before you begin programming
the terminal.
•

Chapter 1, ‘‘VT420 Features,’’ provides an overview of the terminal.
The chapter briefly describes the terminal’s major features and
operating modes.

•

Chapter 2, ‘‘Character Encoding,’’ describes the character-encoding
concepts used by the VT420. The chapter also describes the terminal’s
character sets, the format for control functions, and commands for
using macros.

Part 2: Control Functions Sent to the Host
Part 2 covers the codes sent from the keyboard.
•

Chapter 3, ‘‘ANSI, Short ANSI, and PC Keyboard Codes,’’ describes
the characters and control functions that the terminal sends to the
host.

Part 3: Control Functions Received from the Host
Part 3 covers the control functions you can use to program the terminal
in VT mode or PC TERM mode. Part 5 describes features unique to PC
TERM mode.
•

Chapter 4, ‘‘Emulating VT Series Terminals,’’ describes the control
functions used to emulate Digital’s other VT series terminals.

•

Chapter 5, ‘‘Using Character Sets,’’ describes the control functions
used to select the terminal’s built-in character sets and your own soft
character sets.

•

Chapter 6, ‘‘Page Memory,’’ describes the control functions used to
format and move through the terminal’s page memory.

•

Chapter 7, ‘‘Setting Visual Character and Line Attributes,’’ describes
the control functions used to highlight text, such as bolding and
underlining.

•

Chapter 8, ‘‘Editing,’’ describes the control functions used to edit
characters in the terminal’s page memory.

About This Manual

xix

•

Chapter 9, ‘‘Rectangular Area Operations,’’ describes the control
functions used to manipulate rectangular areas of text.

•

Chapter 10, ‘‘Cursor Movement and Panning,’’ describes the control
functions used to move the cursor and pan through data in page
memory.

•

Chapter 11, ‘‘Keyboard, Printing, and Display Commands,’’ describes
the control functions used to program the terminal’s keyboard, printer
port, and display screen.

•

Chapter 12, ‘‘VT420 Reports,’’ describes the control functions used to
request reports on the operating state of the terminal. The chapter
also describes the format of the reports sent by the terminal, and the
control functions use to restore the terminal to a previous state.

•

Chapter 13, ‘‘Resetting and Testing the Terminal,’’ describes the
control functions used to reset and test the terminal’s operating
features.

Part 4: Dual Sessions
Part 4 describes two methods for managing sessions on the VT420—
multiple system communications (MSC) and SSU software.
•

Chapter 14, ‘‘Session Management,’’ describes MSC and SSU. The
chapter also lists shared and independent resources available to each
session when you use two sessions.

Part 5: Emulating a Personal Computer
Part 5 describes how the VT420 model with PC TERM mode can emulate
a personal computer (PC).
•

Chapter 15, ‘‘Operating in PC TERM Mode,’’ describes how the
terminal operates in PC TERM mode. The chapter describes control
characters, PC character sets, and codes the PC keyboard sends to the
host.

Appendices
•

Appendix A, ‘‘VT52 Mode Control Codes,’’ describes control functions
used when the terminal is in VT52 mode.

•

Appendix B, ‘‘Communication,’’ describes how the terminal
communicates with the host system and local devices, such as modems
and printers. The appendix also provides cabling information and
describes how to connect to non-Digital systems.

xx About This Manual

•

Appendix C, ‘‘Related Documentation,’’ lists other VT420
documentation you can order from Digital.

•

Appendix D, ‘‘Compatibility with Other Digital Terminals,’’ compares
the VT420 video terminal to Digital’s VT320 and VT220 video
terminals.

Conventions
The following conventions are used in this manual:
Notes

Provide general operating information.

Programming tips

Provide helpful suggestions to consider when writing
applications.

Set-up features

The names of features appear in bold type.
Example: Use the save feature in the Set-Up
Directory screen.
Set-up feature settings and fields appear in this
type.
Example: The cursor is on the Global field in the
Set-Up Directory.

ANSI keyboard keys

Appear as normal text in a box .
Example: Press the Return key.

PC keyboard keys

Appear as bold text in a box .
Example: Press the Enter key.

ANSI keys (with PC
keys)

When a PC command sequence differs from an ANSI
command sequence, the PC key sequence appears in
parentheses after the ANSI sequence.
Example: Press the Return key ( Enter ).

Ctrl key

For Ctrl key sequences, hold down Ctrl and press the
other key.

Characters in control
functions

Appear in bold type. Variables appear in italics.
Below each character is a column/row number that
indicates the character’s position in a standard code
table.
Example:
ESC
1/11

#
2/3

6
3/6

Control function
Column/row
numbers

About This Manual

Glossary entries

xxi

Appear in italics when first used in text.
Example: The VT420 stores information in its page
memory.

Part 1
Introduction to Your
VT420 Terminal

VT420 Features

This chapter provides an overview of the VT420 video terminal. The
chapter briefly describes the major features and operating modes of the
terminal.

VT420 Models
The VT420 is a monochrome text terminal. The terminal has two major
components, a monitor/terminal unit and a keyboard. The monitor has a
tilt-swivel base.
The VT420 is available in three models: worldwide, worldwide with PC
TERM mode, and North American.
•

The worldwide model supports 8-bit multinational character sets
and several 7-bit national replacement character sets (NRCs) for
western Europe. This model has two system communication ports
(6-pin, DEC-423 port and 25-pin, RS-232 port) and a detachable power
cord.

•

The worldwide model with PC TERM mode provides all the
features of the worldwide model, plus an operating mode that supports
personal computer (PC) character sets and PC application software.

•

The North American model is similiar to the worldwide model,
but does not support the NRC sets or PC TERM mode. This model
has one system communication port (6-pin, DEC-423 port) and an
attached power cord.

Chapter 1

4 VT420 Features
VT420 Models

All models have a 6-pin, DEC-423 printer port. The printer port can also
serve as an extra communication port for connection to a host computer.
Users can select whether this port acts as a local printer port or an extra
communication port, by setting a feature in the Global Set-Up screen.
This manual covers the programming information you need to use the
features for the terminal. The terminal uses control functions specified by
the American National Standards Institute (ANSI) and the International
Organization for Standardization (ISO).

Keyboards
The terminal uses one of three Digital keyboards (Figure 1–1):
•

ANSI keyboard

•

Short ANSI keyboard

•

PC keyboard (with 101 or 102 keys)

The ANSI and PC keyboards are available in various models for different
languages. The PC keyboard is for the VT worldwide model with PC
TERM mode; the North American model has 101 keys, and other models
have 102 keys. You can use the ANSI and short ANSI keyboards with any
VT420 model. See Installing and Using the VT420 Video Terminal with
PC Terminal Mode for a comparison of the three keyboards.
The next section describes some of the important new features of the
terminal.

Chapter 1

VT420 Features
VT420 Models

KEYBOARD 102

3
LJ-01105-TI0

Figure 1–1

VT420 Video Display Terminal with Keyboards

ANSI keyboard

Short ANSI keyboard

PC keyboard (102-key model shown)

Chapter 1

6 VT420 Features
New Features

New Features
The VT420 is compatible with Digital’s VT320 terminal and offers major
new features, such as the ability to use PC applications, two sessions, and
two windows. You can also create macros and perform rectangular area
editing. Local page memory provides faster on-line transaction processing.

PC TERM Mode
The VT420 worldwide model with PC TERM mode supports PC character
sets and PC application software. Chapter 15 describes PC TERM mode
and PC character sets.

Two Sessions
When you electronically connect to a host system from your terminal, you
start an interactive session. The VT420 lets you run two sessions at the
same time. That is, you can connect to two different jobs on your system.
If you connect your VT420 to two systems, you can log in to both systems
and run those sessions at the same time. If you are using a PC keyboard,
you can select a different operating mode for each session — VT mode
or PC TERM mode. If you connect your VT420 to a terminal server that
supports several systems, you can run two VT mode sessions, each on a
different system.
The two-sessions feature gives you two terminals in one. The VT420
maintains the two sessions separately. You can easily switch back and
forth between the two sessions from the keyboard.
The VT420 has two different methods for managing dual sessions,
multiple system communications (MSC) and Digital’s SSU protocol.
•

MSC
Uses two separate communication lines to maintain two sessions at
the same time.

•

SSU (VT mode only)
Uses one communication line and Digital’s proprietary SSU software
protocol to maintain two sessions at the same time. The SSU protocol
is available as a separate VMS layered software product or as part of
a DECServer 200, DECserver 300, or DECserver 500 system.

You can select different operating features for each session. For example,
you can use different set-up selections, page memory format, and userdefined keys.
For more information on session management, see Chapter 14.
Chapter 1

VT420 Features
New Features

User Windows
The VT420 lets you view data from two sessions at the same time. To
view data from two sessions, you divide the screen into two windows.
By default, each session you open with a VT420 terminal uses the
complete screen. This means the terminal can only display data from
one session at a time. To divide the screen into two windows, you press a
sequence of keys. Each window is assigned to a session. Information from
one session appears in one half of the screen, information from the second
session appears in the other half.
You can divide the screen horizontally. When you divide the screen, a
border appears across the middle of the screen from column 1 to the last
column.
For more information on user windows, see Installing and Using the
VT420 Video Terminal.

Page Memory
In VT mode, the VT420 has a multiple-page display memory. The
multiple-page feature lets the terminal store more text than appears
on the screen. For example, when you use two sessions the terminal
can store up to three screen areas of text (three 24-line pages) for each
session.
In PC TERM mode, the host system stores data.
Page memory provides a storage space for pop-up menus and a means
for instant screen updates. You can select different page sizes. The page
sizes available depend on whether you are running one or two sessions.
Two Sessions
•

3 pages of 24 lines

80 or 132 columns

•

2 page of 25 lines

80 or 132 columns

•

2 pages of 36 lines

80 or 132 columns

•

1 page of 48 lines

80 or 132 columns

•

1 page of 72 lines

80 or 132 columns

One Session
•

6 pages of 24 lines

80 or 132 columns

•

5 pages of 25 lines

80 or 132 columns

•

4 pages of 36 lines

80 or 132 columns
Chapter 1

8 VT420 Features
New Features

•

3 pages of 48 lines

80 or 132 columns

•

2 pages of 72 lines

80 or 132 columns

•

1 page of 144 lines

80 or 132 columns

A page is a section of the terminal’s page memory. Each page has left,
right, top and bottom margins. You can define the size and layout of a
page by using set-up features or control functions.
For more information on page memory, see Chapter 6.

Macro Feature
This feature lets you download ANSI text and commands into the
terminal. The terminal stores the text and commands until you invoke
them with a control function. The macro feature provides you with more
convenience and flexibility. It lets you execute a group of ANSI control
functions as a set. For more information, see Chapter 2.

Rectangular Area Operations
This feature lets you manipulate rectangular areas of text within page
memory. You can
•

Copy them from one area in page memory to another.

•

Erase them.

•

Fill them with a character of your choice.

•

Change or reverse their visual character attributes.

For more information, see Chapter 9.

Local Copy and Paste Feature (VT Mode)
This feature lets you copy text from the screen to an internal buffer. You
can later send the text to the host. This feature is useful for copying text
from the terminal screen to the host application.

Number of Lines/Screen
The VT420 has three different character font heights, so users can
display 24, 36, or 48 lines of text on the screen. For more information,
see Chapter 11.

Chapter 1

VT420 Features
General Features

General Features
This section describes the general operating and communication features
of the terminal. You can set many of these features from the keyboard,
using set-up.

Set-Up
Set-up is a series of display screens. Each screen lists a group of features,
such as communications or printing.
You can use set-up screens to examine and change the current settings for
features. For example, you can select the keyclick feature, transmit and
receive speeds, page size, and type of session management.
The VT420 set-up feature is similar to the VT320 set-up feature.
Installing and Using the VT420 Video Terminal describes the set-up
screens in detail.

Display Features
The VT420 screen has the following basic features:
•

359 mm (14-inch), flat-screen monitor

•

24, 36, or 48 display lines at a time
800 (horizontal)

•

400 (vertical) pixels

A separate status line for each session, at the bottom of the screen
(You can disable the status line to have an additional line for data
display.)

•

Horizontal split-screen scrolling on any line boundary
(same as the VT100)

Text Features
The VT420 provides a variety of text and editing features.
•

Character sets
– 5 sets of 94 characters each
– 1 set of 96 characters
– National replacement character sets (worldwide model)
– 3 PC sets of 128 characters each (worldwide model with PC TERM
mode)
– Downloadable character set (94 or 96 characters)
Chapter 1

10 VT420 Features
General Features

•

ANSI keyboard function keys
– 5 local function keys
– 15 user-definable keys
PC keyboard function keys
– 3 local function keys
– 30 user-definable keys (VT mode)
51 user-definable keys (PC TERM mode)
PC keyboard scan codes sent to the host

•

All VT320 editing functions

•

Normal, bold, underline, blinking, and reverse video characters

•

Single-width/single-height lines
Double-width/single-height lines
Double-width/double-height lines

•

Control characters and functions
– 7-bit and 8-bit control characters
– ANSI control functions
– DEC private control functions
– Ability to display control functions

•

Character Sets
The VT420 has the following built-in character sets:
•
•
•
•
•
•
•

ASCII
DEC Supplemental Graphic
ISO Latin Alphabet Nr 1 supplemental graphic
National replacement character sets (NRCs)
(worldwide model)
DEC Technical
DEC Special Graphic (VT100 line drawing)
PC character sets (worldwide model with PC TERM mode)
— PC International
— PC Multilingual
— PC Danish/Norwegian
— PC Portuguese
— PC Spanish

You can also design a soft character set, then load it from the host system
into the terminal.

Chapter 1

VT420 Features
General Features

Together, the ASCII and DEC Supplemental Graphic sets make up the
DEC Multinational character set. When you turn on or reset the
terminal, the VT420 automatically uses the DEC Multinational set.
The ASCII and ISO Latin-1 supplemental sets make up the ISO Latin-1
character set.
Chapter 2 describes the VT420 character sets. Chapter 5 describes how to
select and use different character sets.

Communication Features
The VT420 provides the following features for communicating with the
host system:
•

7-bit or 8-bit environments

•

XPC communication protocol, which defines the XON and XOFF
points

•

Asynchronous communication speeds up to 38,400 bits/second

•

One DEC-423 host port

•

One RS-232 host port, with a 25-pin D-subminiature connector for a
host or external modem (worldwide model only)

•

One bidirectional DEC-423 printer port, which also serves as a
communication port with a host system

The VT420 has two major communication states, on-line and local. You
select the communication state in set-up.
•

The on-line state lets the terminal communicate with a host system.
The terminal sends data entered at the keyboard to the host. The
terminal displays data received from the host on the screen.

•

The local state lets you place the host system on hold. Data entered
at the keyboard is sent to the screen, but not to the host. The
terminal stores data received from the host, until you put the terminal
back on-line.

Chapter 1

12 VT420 Features
Operating Modes

Operating Modes
The VT420 has four major operating modes for text operations. The
VT420 with PC TERM mode has five major operating modes. You can
select each mode from the keyboard (using set-up screens), or from the
host (using control codes). The VT420 uses standard ANSI functions in
all operating modes, except VT52 mode and PC TERM mode.
VT400 mode, 7-bit controls
VT100 mode
VT400 mode, 8-bit controls
VT52 mode
PC TERM mode
VT400 mode, 7-bit controls is the default operating mode. This mode
provides the full range of VT420 capabilities, using 8-bit characters and
7-bit control characters. All character sets are available. This mode
provides full compatibility with Digital’s VT300 series terminals. Digital
recommends this mode for most applications.
VT400 mode, 8-bit controls provides the full range of VT420
capabilities, using 8-bit characters and 8-bit control characters. All VT
mode character sets are available, and the terminal recognizes both 7-bit
and 8-bit controls.
In this mode, the terminal can run VT300 applications that use 8-bit
control characters. The worldwide model with PC TERM mode can use
a PC keyboard. The terminal operates most efficiently in this mode, but
some systems and applications do not yet support 8-bit operation.
PC TERM mode enables the terminal to support PC application software
and character sets. The terminal sends scan codes to the host, which PC
applications recognize. The terminal sends scan codes when you press a
key and when you release a key. This mode requires a PC keyboard.
VT100 mode provides full compatibility with Digital’s VT102 terminal.
This mode restricts the terminal to a 7-bit environment. The keyboard is
restricted to VT100 keys, and the only available character sets are ASCII,
national replacement characters, and DEC Special Graphic. You can use
this mode with applications that require strict VT100 compatibility.
VT52 mode provides full compatibility with Digital’s VT52 terminal.
This mode only uses Digital’s private control functions, not standard
ANSI functions. You use this mode with applications written for the
VT52.
Chapter 2 describes the format for 7-bit and 8-bit character codes.
Chapter 4 describes how the VT420 can emulate other VT series
terminals.

Chapter 1

22
Character Encoding

This chapter describes the character-encoding system that the terminal
uses in VT mode to communicate with a host system. See Chapter 15 for
a description of PC TERM mode. You must have a basic understanding
of the character-encoding system described in this chapter before you use
the control functions in the rest of this manual.
The chapter also describes the character sets available in VT mode and
the format for sending control functions to the terminal. You can select
character sets for different countries or for special uses, such as technical
characters. You use control functions to make the terminal perform
special functions, such as editing or printing.

Overview
The VT420 uses a communication line to exchange information with a
host system. The terminal and the host send data in an encoded form
that is different from what you see on the screen.
In VT mode, the keys you type on your keyboard send scan codes to the
terminal. The terminal converts the scan codes to character codes or
ANSI control functions, then sends the information to the host. The host
stores the information and passes it to application software programs. For
example, your host may have applications that let you do word processing,
data entry, or programming.
The host processes the output from the application software and displays
it on the terminal’s screen. You can print the data by sending it to a
printer connected to the terminal.

Chapter 2

14 Character Encoding
Overview

Host
Computer
ASCII Characters
ANSI Control Sequences

VT420
Terminal

VT Mode

(VT400, VT300, VT200, VT100, VT52)
ANSI
Keyboard
Short ANSI
Keyboard

(VT400, VT300, VT200, VT100)
PC
Keyboard
LJ-01476-TI0

Figure 2–1

VT Mode Operation

Coding Standards
All terminals and computers encode information as binary digits, or bits.
Older systems use 7 bits to encode each character. Newer systems such as
the VT420 use 8 bits, which provide more codes. The newer systems can
also use the 7-bit codes.
The VT420 uses an 8-bit character-encoding system and a 7-bit code
extension technique. The ‘‘7-Bit Code Extension Technique’’ section in this
chapter explains what 7-bit code extensions are.
The American National Standards Institute (ANSI) and International
Organization for Standardization (ISO) specify standards for character
encoding in the information-processing industry. The VT420 terminal is
compatible with the following ANSI and ISO standards.

Chapter 2

Character Encoding
Coding Standards

Standard

Description

dpANS X3.134.1

8-Bit ASCII structure and rules

dpANS X3.134.2

Code for information interchange of 7-bit and
8-bit ASCII supplemental multilingual graphic
character set

ANSI X3.4—1977

American Standard Code for Information
Interchange (ASCII)

ANSI X3.41—1974

Code Extension Techniques for Use with the 7-Bit
Coded Character Set of American National Code
Information Interchange

ANSI X3.32—1973

Graphic Representation of the Control Characters
of American National Code for Information
Interchange

ANSI X3.64—1979

Additional Controls for Use with American
National Standard for Information Interchange

ISO 646—1977

7-Bit Coded Character Set for Information
Processing Interchange

ISO 2022

7-Bit and 8-Bit Coded Character Sets—Code
Extension Techniques

ISO 6429

Additional Control Functions for Character
Imaging Devices

ISO 8859-1

8-Bit single byte code graphic character sets-Part
1: Latin Alphabet Nr 1

ISBN 2-12-953907-0

ISO international register of character sets used
with escape sequences

You can order ANSI and ISO standards from the following sources:
ANSI Standards
Sales Department
American National Standards Institute
1430 Broadway
New York, NY 10018
ISO Standards
CCITT
UN Book Store
United Nations Building
New York, NY 10017

Chapter 2

16 Character Encoding
Characters and Character Sets

Characters and Character Sets
In Digital’s computing environment, a character is a symbol represented
by an 8-bit binary code. These symbols include letters, digits, and
punctuation marks, as well as other symbols used to organize, control,
or represent data.
Here are a few examples of characters and their corresponding 8-bit codes.
Character

Code

01000001

}

01111101

CSI

10011011

There are two types of computing environments, 7-bit and 8-bit. In a
7-bit environment, only the last 7 bits of the character code define the
character. In an 8-bit environment, all 8 bits define the character.
The A character above is defined in a 7-bit or 8-bit environment, because
the eighth bit of the code is 0. The 8-bit form of the CSI character is
defined only in a 8-bit environment, because its eighth bit is 1.
A coded character set is a group of characters that conform to certain
rules and standards. These standards are set by organizations such ANSI
and ISO. Each character in a character set is represented by a different
combination of 8 bits.

Code Table
A code table is a convenient way to show all the characters in a character
set with their codes. Most standard character sets put similar characters
into groups, so they have similar codes. A code table lets you see groups
of characters and their relative codes clearly.
There are two basic types of characters, graphic characters and control
characters. These two character types are defined by ANSI and ISO
standards. The VT420 processes received characters based on these two
character types.
Graphic characters are characters you can display. Graphic characters
include letters, numbers, punctuation marks, and any other characters
you can display.
Control characters are characters you do not usually display. They
make the terminal or host system perform specific functions in data
communications and text processing.

Chapter 2

Character Encoding
Code Table

NOTE
You can display control characters on the screen, to help you
debug your applications. To display control characters, you set
the control representation mode feature in the Display Set-Up
screen to Display Controls. See the ‘‘Display Controls Mode’’
section at the end of this chapter.
This section describes the format for 7-bit and 8-bit code tables.

7-Bit ASCII Code Table
Figure 2–2 is the 7-bit ASCII code table. The table has 128 character
codes, arranged in 8 columns and 16 rows.
Every character in a row uses the same binary code for its four least
significant bits (Figure 2–3). This value appears at the left of each row.
For example, every character in row 0 uses the binary code 0000 for its
four least significant bits.
Every character in a column uses the same binary code for its three
most significant bits. This value appears at the top of each column. For
example, every character in column 0 uses the binary code 000 for its
three most significant bits.
The ASCII table also shows the octal, decimal, and hexadecimal code for
each character. Different programmers may prefer using octal, decimal,
or hexadecimal codes for different purposes.
This manual refers to characters by their position in the table. For
example, the character H is at 4/8 (column 4, row 8). You can use the
column/row number to find a character and its codes in the table. For
example
ESC
1/11

#
2/3

6
3/6

means
The ESC character is at column 1, row 11.
The # character is at column 2, row 3.
The 6 character is at column 3, row 6.
The ASCII graphic characters are in positions 2/1 through 7/14 of the
ASCII table. ASCII graphic characters include all American and English
alphanumeric characters, plus punctuation marks and various text
symbols. Examples are C, n, ", !, +, and $. (The British pound sign is
not an ASCII graphic character.)

Chapter 2

18 Character Encoding
Code Table

Column

Bits

0
0

Row

0
0

0
1
1

0
1

1
1

0
0
0
1
1
1
2
2
2
3
3
3
4
4
4
5
5
5
6
6
6
7
7
7
10
8
8
11
9
9
12
10
A
13
11
B
14
12
C
15
13
D
16
14
E
17
15
F

20
16
10
21
17
11
22
18
12
23
19
13
24
20
14
25
21
15
26
22
16
27
23
17
30
24
18
31
25
19
32
26
1A
33
27
1B
34
28
1C
35
29
1D
36
30
1E
37
31
1F

40
32
20
41
33
21
42
34
22
43
35
23
44
36
24
45
37
25
46
38
26
47
39
27
50
40
28
51
41
29
52
42
2A
53
43
2B
54
44
2C
55
45
2D
56
46
2E
57
47
2F

60
48
30
61
49
31
62
50
32
63
51
33
64
52
34
65
53
35
66
54
36
67
55
37
70
56
38
71
57
39
72
58
3A
73
59
3B
74
60
3C
75
61
3D
76
62
3E
77
63
3F

100
64
40
101
65
41
102
66
42
103
67
43
104
68
44
105
69
45
106
70
46
107
71
47
110
72
48
111
73
49
112
74
4A
113
75
4B
114
76
4C
115
77
4D
116
78
4E
117
79
4F

120
80
50
121
81
51
122
82
52
123
83
53
124
84
54
125
85
55
126
86
56
127
87
57
130
88
58
131
89
59
132
90
5A
133
91
5B
134
92
5C
135
93
5D
136
94
5E
137
95
5F

140
96
60
141
97
61
142
98
62
143
99
63
144
100
64
145
101
65
146
102
66
147
103
67
150
104
68
151
105
69
152
106
6A
153
107
6B
154
108
6C
155
109
6D
156
110
6E
157
111
6F

160
112
70
161
113
71
162
114
72
163
115
73
164
116
74
165
117
75
166
118
76
167
119
77
170
120
78
171
121
79
172
122
7A
173
123
7B
174
124
7C
175
125
7D
176
126
7E
177
127
7F

b4 b3 b2 b1
0

NUL

SOH

STX

ETX

EOT

ENQ

ACK

BEL

11 1

12 1

13 1

14 1

DLE
DC1
(XON)

DC2
DC3
(XOFF)

DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US

!
"
#
$
%
&
’
(
)
*
+
,
.
/

0
1
2
3
4
5
6
7
8
9
:
;
<
=
>

C0 Codes

@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O

P
Q
R
S
T
U
V
W
X
Y
Z
[
\
]
^
_

‘
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o

p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL

GL Codes (ASCII Graphic)

Key
Character

ESC

33
27
1B

Octal
Decimal
Hex
GSF_0586_89.DG

Figure 2–2

Chapter 2

7-Bit ASCII Code Table

Character Encoding
Code Table

Bit
7

Bit
6

Bi t
5

Bi t
4

Bi t
3

Bi t
2

Bi t
1

3 M ost
S i g n i f i c an t Bi ts

4 L e a st
Si g n i fi ca n t Bi ts

(D e c i m a l Va l u e i s
Column in
Code Table)

( D e ci m a l Va l u e i s
Row in
C o d e Ta b l e )
GSF_0583_89.DG

Figure 2–3

7-Bit Code

The ASCII control characters are in positions 0/0 through 1/15 (columns
0 and 1) of the ASCII table. The SP character (2/0) may act as a graphic
space character or a control character, depending on the context. DEL
(7/15) is always a control character.
ANSI and ISO standards define control character codes and their
functions. These standards also define the mnemonic used to represent
each control character in a code table. Here are some examples of ASCII
control characters with their mnemonics.
ASCII Control Character

Mnemonic
(Appears in Code Table)

Carriage return

Form feed

Cancel

CAN

Chapter 2

20 Character Encoding
Code Table

8-Bit Code Table
Figure 2–4 shows the format for an 8-bit code table. It has the same
number of rows as the 7-bit table, but twice as many columns and
character code positions.
Each character in a row of the 8-bit table uses the same binary code for
its four least significant bits (Figure 2–5). Each character in a column
uses the same binary code for its four most significant bits.
The codes on the left half of the 8-bit table (columns 0 through 7) work
like the codes in the 7-bit table. You can use these codes in a 7-bit or 8-bit
environment. The eighth bit of these codes is 0.
The codes on the right half of the table (columns 8 through 15) have an
eighth bit of 1. You can only use these codes in an 8-bit environment.
The 8-bit code table has two sets of control characters, C0 (control zero)
and C1 (control one). The VT420 uses the ANSI definitions for the
functions of C0 and C1 controls. The C0 controls are in columns 0 and 1.
The C0 controls are the same as the ASCII control characters in the 7-bit
table. You can use C0 controls in a 7-bit environment.
The C1 controls are in columns 8 and 9. They perform different functions
than the C0 controls. You can only use C1 controls directly in an 8-bit
environment. You can select C1 codes indirectly in a 7-bit environment.
The ‘‘7-Bit Code Extension Technique’’ section in this chapter explains
how to select C1 controls indirectly. Some C1 code positions are blank,
because their functions are not yet standardized.

Chapter 2

Character Encoding
Code Table

Col umn
00

NUL

DLE

SOH

DC1

PU1

STX

DC2

PU2

ETX

DC3

STS

EOT

DC4

IND

CCH

ENQ NAK

NEL

ACK

SYN

SSA

SPA

BEL

ETB

ESA

EPA

CAN

HTS

HTJ

SUB

VTS

ESC

PLD

CSI

PLU

OSC

SS2

SS3

APC

Row

C0 Codes

DCS

DEL

GL Codes

C1 Codes

GR Codes

7- Bi t Co d e Ta b l e

GSF_0584_89.DG

Figure 2–4

8-Bit Code Table

Chapter 2

22 Character Encoding
Code Table

Bit
8

Bit
7

Bi t
6

Bi t
5

Bi t
4

Bi t
3

Bi t
2

Bi t
1

4 M o st
S i g n i f i c a n t Bi ts

4 L e a st
Si g n i fi ca n t Bi ts

(D e c i m a l Va l u e i s
Column in
Code Table)

( D e ci m a l Va l u e i s
Row in
C o d e Ta b l e )
GSF_0585_89.DG

Figure 2–5

8-Bit Code

NOTE
The VT420 does not recognize all C0 and C1 codes. Tables 2–2 and
2–3 list the codes the terminal recognizes. The terminal generally
ignores all other control codes.
The table also has two sets of graphic characters, GL (graphic left) and
GR (graphic right). There are 94 GL codes in positions 2/1 through 7/14.
You can use GL codes in 7-bit or 8-bit environments.
There are 96 GR codes in positions 10/0 through 15/15. Some 8-bit
character sets only use 94 of these GR codes. You can use GR codes
only in an 8-bit environment.
Together, the GL and GR sets make up the terminal’s in-use table. The
in-use table contains the graphic characters the terminal can currently
use. Before the terminal can display and send characters from a character
set, the set must be mapped into the in-use table. Chapter 5 describes the
in-use table in detail.

Chapter 2

Character Encoding
VT420 Character Sets

VT420 Character Sets
The VT420 provides the following built-in graphic character sets:
ASCII
DEC Supplemental Graphic
ISO Latin Alphabet Nr 1 supplemental graphic
National replacement character sets (NRCs)
DEC Special Graphic
DEC Technical
See Chapter 15 for additional sets available in PC TERM mode. You can
also design and load a soft character set into the terminal.
Downloadable (soft) set
All VT420 character sets contain graphic and control characters. The
function of control characters never change, no matter what character
set you use. The terminal always interprets C0 and C1 control codes as
defined by ANSI.
The terminal stores the codes for graphic characters in GL and GR
tables. Selecting a new character set changes the characters associated
with the GL or GR codes. When you turn on or reset the terminal, you
automatically select the following character sets:
ASCII in GL
DEC Supplemental (or ISO Latin-1 supplemental) graphic in GR
Together, the ASCII set and one of the supplemental sets make up a
multinational character set.
•

The ASCII set and DEC Supplemental Graphic sets are known as the
DEC Multinational character set.

•

The ASCII set and the ISO Latin-1 supplemental set are known as
the ISO Latin Alphabet Nr 1 set.

You select the supplemental set with (1) the UPSS (user-preferred
supplemental set) feature in the General Set-Up screen, or (2) the
assign user-preferred supplemental set (DECAUPSS) control function
(Chapter 5).

Chapter 2

24 Character Encoding
VT420 Character Sets

DEC Supplemental Graphic Character Set
This 8-bit character set has 94 graphic characters. The graphic characters
include accented letters and diacritical marks, used in many European
languages. There are also special symbols, such as currency signs.
When you first turn on your terminal, you automatically select the ASCII
character set and the DEC Supplemental Graphic set. The terminal maps
the ASCII set into its GL table, and the DEC Supplemental Graphic set
into its GR table. Together, these two character sets are known as the
DEC Multinational character set (Figures 2–6 and 2–7).
0

Column

Bits

0
0

b6
b5
Row

b4 b3 b2 b1

NUL

SOH

STX

ETX

EOT

ENQ

ACK

BEL

10 1

11 1

13 1

14 1

15 1