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DIGITAL-8-1-U

December 1965

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Document:	digital-8-1-u-d
Order Number:	DIGITAL-8-1-U
Revision:
Pages:	8
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/digital-8-1-u/digital-8-1-u-d.pdf

OCR Text

IDENTIFICATION
Product Code:

DEC-08-LRAA-D

Product Name :

Read-In-Mode Loader

Date Created:

February 23, 1965

Maintai ner :

Software Services Group

D EC-08-LRAA-D
\

ABSTRACT
The Rim Loader i s a minimum-sized routine for reading and storing information contained in

Read-In-Mode coded tapes v i a the ASR-33 perforated tape reader.

REQUIREMENTS

2.1

Storage

17 decimal (21 octal).

2.2

Equi pment

4K PDP-8 with ASR-33.

--.

USAGE

3.1

Load inq
To place the Rim Loader into memory v i a the control console switches, proceed as follows:

3.1 .1

Set 7750 i n the switch register (SR).

3.1.2

Press LOAD ADDRESS.

3.1 .3

Set the first instruction (6032) in the S R .

3.1 .4

Press DEPOSIT.

3.1 .5

Set the next instruction (6031) i n the SR.

3.1.6

Press DEPOSIT.

3.1 .7

Repeat steps 3.1.5 and 3.1.6

3.2

Calling Sequence
None.

until a l l instructions have been deposited.

Cannot be called as a subroutine.

D EC -08 -L R AA.-D
3.3

Start-up/Entry

3.3.1

Place the perforated tape which must be i n RIM format in the pertoroicid-tape reader.

3.3.2

Make sure that the ASR-33 i s on line.

3.3.3

Place the starting address 7756 in the switch register.

3.3.4

Press the LOAD ADDRESS key.

3.3.5

Press console START key.

3.3.6

Move the reader control switch to START.

3.4

Errors

There are no error stops in this routine.
/--

DESCRIPTION
This i s a basic routine that alternately assembles aii addi i s frc m t w o s r J c c e s s i v ? characters on

tape, then assembles data contained i n the next t w o characters and stores this data ut the associated ad-

dress.
Because a tape in Rim format i s twice as long as a coriiparable tape i v Binary format, i t i s

suggested that the Rim Loader only be used to read i n the Binai-y Loader. Aftei t h i i , the Binary Loader
should be used.

FORMAT

5.1

External Data
Tapes to be read by this program must be i n Read-In-Mode coded format.

5.1.1

Leader should be about 2 feet o f Leader-Trailer codes (any code with channel 8 punched;

preferably code 200).

5.1.1 .1

Depress ALT MODE, CTRL, and @ keys simultaneously to punch 200 Leader-Trailer.

5.1 .2

Characters representing the absolute, machine language program are arranged i n an alternat-

ing pattern of address, contents, address, contents, etc.
not punched. Contents have no punch i n channel 7 or 8.

5.1.3

Trailer:

5.1.4

Example of Read-In-Mode coded format:

Same as Leader.

Tape Channel
Channels 8 and 7 Indicate-

87 654 S 321

. 000
01 A1 . A2
10 000

00 A3
00 D1
00 D3

.Leader code i s always found first.
Absolute octal Address of data i n next two characters.

. A4

. D2

Octal Data to be stored at preceeding address.

. D4

This pattern repeats i n similar four character groups until the concluding
I

Addresses have channel 7 punched, channel 8

10 000

. 000

Trailer Code i s encountered.

5.1 .4.1

Note that actually a 3-bit group (a single octal character) i s designated by the notation A1

above.

The "1" i n this notation indicates that this particular octal character w i l l be used as the most

significant three bits i n specifying the absolute address into which following data w i l l be deposited.
Correspondingly,

A2, A3, and A4 designate successively less significant octal characters i n the absolute

address.

5.1 .4.2

The remarks i n 5.1.4.1 apply equally to Data as specified by the notation D1, D2, D3, and

D4.

PROGRAM

6.1

Program Listing

Addr

.
-.

Octal
Contents

7756,
7757,

6032
6031

7760,

5357
6036

Abs

7761,

Instruction I Z

Tag

Comments

KCC

BEG,

KSF

AC and flag
/skip i f flag = 1

JMP ,-1
KR 6

/looking for char
/read buffer

/Clear

Abs.
Addr

Octal
Contents

71 06
7006
751 0
5357
7006
603 1
5367
6034
7420
3776
3376
5356
0
JMP start of bin loader

7762,
7763,
7764,
7765,
7766,
7767,
7770,
7771,
7772,
7773,
7774,
7775,
7776,
7777,

ADDENDA

7.1

Other Possible RIM Loaders

Tag

Instruction I Z

CLL RTL
RTL
SPA
JMP BEG+l
RTL
KSF
JMP .-1
KRS
SNL
DCA ITEMP
DCA TEMP
JMP BEG
0
0

TEMP,

Comments

/ch8 i n A C 0
/checking for leader
/found leader
/OK, ch7 i n link

/read, do not clear
/checking for address
/store contents
/store address
/next word
/temp storage

Variations of the RIM Loader described may prove useful i n special cases where, due to c i r -

/--

cumstances, RIM must be located i n a different section of core.
O n the other hand, the equipment involved may make i t necessary to use a variation of RIM
tailored specifically to a particular situation.

As an example of this, consider a special-purpose

PDP-8 system used for text editing. I n this system, no ASR-33's are used. Instead several typewriters
which use a different code (including provision for upper and lower case) are time-shared with respect
to input and output with a central PDP-8.
Please consult the Applied Programming Department at Digital Equipment Corporation for detailesof other RIM Loaders currently available or for assistance i n special cases.

7.2

The Use of PDP-8 System Programs
Certain system programs such as the DECtape Library System (Digital-8-8-5)

require that the

RIM Loader precisely as listed above (6.1) be used.

7.3

Using the RIM Loader with an Extended Memory
The RIM Loader as described and listed up to this point may actually run i n any memory field

provided that i t i s loaded into memory following a slightly different procedure than that described i n 3.1
above.

The Instruction Field register and the Data Field register must both be set to N (a number from 0

i,, 7) where

N indicates the memory field i n which theRIM Loader i s to be placed. This i s easily done.