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XX-A3239-AD

December 1965

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Document:	maindec-803-d
Order Number:	XX-A3239-AD
Revision:
Pages:	8
Original Filename:	https://svn.so-much-stuff.com/svn/trunk/pdp8/src/dec/maindec-803/maindec-803-d.pdf

OCR Text

IDENTIFICATION

1.1

Maindec 803

1.2

PDP-8 Memory Addres.s Test

1.3

Mayll,1965
1

-t--.I_

Ma:ndec 803
Page 1

ABSTRACT

Maindec 803 provides a rough inspection of the performance of the in,emory address register
and the decoder network which selects a given memory cell . Primarily, Maindeci 803 detects errors that
arise from open or shor+ed selection lines.
3.

REQUIREMENTS

3.I

Storage

The program occupies memory cells 0001-0033. It is designed for use with the RIM Loader in
locations 7756-7776. If it is used with a RIM Loader in 7700, change the contents of memory cell 0032
from 0023 to 0101 before starting the test .

Subprograms and/or Subroutines (Not Applicable)
Eciuipment

Standard PDP-8

USAGE

4.I

4.I.I

Turn off the Teletype reader.

4.1.2

Set the SWITCH REGISTER to 7756; press LOAD ADDRESS, the START.

4.1.3

Place the Maindec 803 RIM program tape in the Telefype reader, and turn on the reader.

4.I.4

When the program has been loaded, stop the computer, turn off the reader, and remove the

program tape .

4.2

Calling Sequence (Not Applicable)

4.3

Switch Settings

4.3.I

Star+ing address = 0001

4.3.2

Other settings:

4.4

Start up and/or Entry

none

With the program in memoi.y, set the SWITCH REGISTER I.a dool, press LOAD ADDRESS,
then START.

4.5

Errors in Usage

For any error, the following two stops occur:

Error

C(MA)

0017

EIA

0022

Cause of Error

Contents of the memory cell iust inspected were incorrect. The AC displays the actual c'ontent.s.

The Ac displays +he address of the cell causing the previous error.

Maindec 803
Page 2

4.6

Recovery from such Errors

ln general, the Memory Address Test detects tw6 types of difificulty in the selection network .

If a selection line is open af any point, the memory registers selectable by that line are effectively isolated from the central processor. The program is unable to write information into those cells, or read
information out. Conversely, if two lines are shorted together, information entering or leaving the registers selectable by one line also enters or leaves those selectable by the other. Thus, the same information appears in two different registers.
Errors seldom occur singly. Usually, a pclttern of errors appears throughout the rested portion
of memory which allows the operator to isolate the possible source of trouble . The pattern usually consists

of alternating blocks of erroneous and error-free memory cells.
isolate the source of trouble .

The following can be used as a guide to

4.6.I

lion,andthe::]t[hoew:nr;°iso°dcui::::o:']°dc::°cfh::£§dr:eg:Sters°rm°rerthetroubleliesintheX-axisse|ec_
Module Type

Module position

Drawing Number

G203
G203
G203
G203
G203
G203

D8012

G203
G203
G603
G603
G603
G603

D8012

D8012
D801 2
D8012
D8012

D8012

D801 2
D8012
lD8012

4.6.2
and the foHow]ifn:A:oedr:::Ss :;::|d:nbeb[c°hcekcsk°efd778 reg:Sters °r less/ the trouble lies in the y-axis selection,

Module Type

G203
G203
G203
G203
G203
G203

G203
G203
G603
G603
G603
G603

Module position

Drawing Number
D8013

D8013
D8013
D8013
D8013
D8013
D8013

D8013
D8013

D8013
D8013
D8013

Maindec 803
Page 3

4.6.3

After an error halt, the test is resume`d by following these |rocedures:

Recovery

Record the c(AC).

Press CONTINUE to reat:h the next halt.

EIA

Record the c(AC).

Press CONTINUE to resume the test.

RESTRICTIONS (Not Applicable)
DESCRI PTI ON

Discussion

The program deposits in each memory register a quantify equal to the address of that register,
and then reads the contents of the same register. If the deposit and read operations were successful, it
continues to the next cell in sequence. After all the testable area of memory has been checked in this
manner, the progi.am I.eturns to the beginning of that area and attempts to read the content.s of each cell .
If this is successful, it ref.urns to the first procedure, depositing informatiion and immediately reading i+.
The test continues to alternate these operations, first making one pass through the I.es fed area performing

the write-then-read check, then making a second, read-only pass.
If an error occurs during a write-then-read pass, the writing is suppressed for the remainder
of the pass, to insure that errors further along are not obliterated .

6.2

Examples and/or Applications

Maindec 803 is useful as a rough check of the memory selection networks when performing
routine maintenance rests. It can also be used i.o confirm an operator`s suspicions if trouble occurs during
the normal operation of the computer. Generally, however, troubles ariising from failures in the address
selection of memory read-write circuits are likely to require the attentiQn of a field service engineer.
7.

METHODS (Not Applicable)

FORMAT (Not Applicable)

EXECUTION TIME

The program will run indefinitely, taking approximately 1.3 .seconds for each pass until an
error is encountered or until the operator stops the computer manually .
10.

PROGRAM

10.I

Core Map (None)

10.2

Dimension List(s) (None)

10.3

Macro, Parameter, and Variable Lists (None)

Maindec 803
Page 4
10.4

Program Listing

/MAINDEC

803!

PDP®g

MEMORY

ADDRESS

TEST!

/I NI TI ALIZ I

BGI N '

/CLEVER

DODGE

/WRITING THIS
/NO.
G0 READ

INITIALIZE

ADRS

PASS?

/Y ES .
/READ

&COMPARE

/YES.
ADRS

G0 0N

/NO
/ERROR:

/AC
CLA

CMA

AND

ADRS

ADRS,

SHOWS

IT?

JMP^

/NO,

CML

/YES,

q023
.0

INCORRECT

CORRECT

/END 0F PASS

/IS

BGIN+I

SHOWS

/IMPLEMENTATI0N OF
/THE CLEVER DODGE

TAD CTAB
SZA CLA

JMP

CTAB,

CML

TEST.

WORD

NEXT PASS

^DDRE:SS.

WORD

Maindec 803
Page 5
DIAGRAMS

Flow Chart

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