Digital PDFs

DIGITAL-7-56-M

July 1965

8 pages

Original

0.2MB

Document:	MAINDEC 703 MemAdrTest
Order Number:	DIGITAL-7-56-M
Revision:
Pages:	8
Original Filename:	http://bitsavers.org/pdf/dec/pdp7/DIGITAL-7-56-M_MAINDEC_703_MemAdrTest_Jul65.pdf

OCR Text

1•

IDENTIFICATION

1 •1

MAINDEC 703

1 .2

PDP-7 Memory Address Test

1 .3

July 7, 1965

PDP

LIBRARY

Maindec 703
Page 2

ABSTRACT

The Memory Address Test is designed to provide a rough inspection of the
performance of the memory address register and the decoder networks which select a given
cell. Maindec 703 will operate in and test memories of any available capacity from 4096 to
32,768 words.

REQUIREMENTS

3. 1

Storage

The program occupies memory registers 00000-00022, in memory field O. In
addition, a short initializing sequence which determines the size of the memory occupies
registers 00023-00044; this sequence is destroyed once the test begins.
3.2

Subprograms
None.

3.3

Equipment

Standard PDP-7 with or without memory extension control and up to three exte nded memory fie Ids.

USAGE

4. 1

4. 1 . 1

Place the HRI program tape in the reader.

4.1 .2

Set the address switches to 00000.

4. 1 .3
C lear the AC switches, then set ACS 3 _4 to indicate the number of addit iona I
memory fields provided, according to the following table:

4.1.4

No. of
Added Fie Ids

Total
Memory Size

0
1
2
3

4K, 8K
12K, 16K
20K, 24K
28K, 32K

Press READ-I N
The program will start automatically.

4.2

Calling Sequence

(Not Applicable)

ACS

0
0
1

1
0

Maindec 703
Page 3
4.3

Switch Settings

4.3.1

Loading Address
00000

4.3.2

Restart Address
00001

4.3.3

Other Settings
AC Switches 3, 4:
Restart:

Number of extended memory fields
EXTEND switch on

Startup

4.4

The program starts automatica lIy after be ing loaded. To restart the program at
any time afterwards, set the address switches to 00001, turn on the EXTEND switch and press
START.
4.5

Errors
The following error stops appear in succession for each error.
.~

~7.

conte~

ERROR:
C(MA):
C(AC) :

E1
00014
Failed bits as l's

The
of the memory cell just exomined were incorrect. The AC lights display the
results of a comparison between the contents of the register and the address of that register.
Bits which did not match are shown as lIs in a field of a's.
ERROR:
C(MA):
C(AC) :

E1A
00016
Address of fa i led ce II

This halt occurs immediately after El.
the error.
4.6

The AC lights display the address of the cell causing

Recovery from such errors
ERROR:
RECOVERY:

El
Record the C(AC). Press CONTINUE.

ERROR:
RECOVERY:

E1A · · "
41';AJ
/ . """ ..",',.. ·-c,'',,-- __',. ~""~" .,(,t:1tXJM..
Record the C(AC).::./Press CONTlNUE'~i

RESTRICTIONS
When restarting the program without reloading it, the EXTEND switch must be on.

Maindec 703
Page 4

DESCRIPTION

6. 1

Discussion

Ma indec 703 tests each register in sequence, from the low end of the testable
area to the highest location, then repeats from the beginning. It continues until an error occurs or unti I the operator stops the computer.
Before the test begins, an initializing routine determines the size of the core
memory in which the test is operating, and accordingly adjusts a constant which sets the upper
limit of the testable area. The number of additional memory fields is obtained from the ACS;
the size of the last field (4K or 8K) is then established, and the limiting constant is adjusted.
The initializing sequence is destroyed when the test begins, so that as much of the memory as
possible is avai lable for testing.
The test passes occur in pairs. During the first, the program deposits in a memory cell a quantity equal in value to the quantity of that cell. If the deposit and read operations were successful, the program continues to the next register in sequence. When a II of
the testable area has been checked by this "write-then-read" procedure, the program goes
back to the beginning of that area and attempts to read the contents of each cell. If this
"read-only" pass is successful, the program begins a new "write-then-read" cycle. The test
continues to alternate the two passes.
When an error occurs during a "write-then-read" pass, the writing is suppressed
for the remainder of that pass, to insure that errors further along are not obi iterated.

6.2

Applications

In general, the address test will catch two kinds of difficulty in the selection
networks. If a se lection Iine is open at any point, the memory registers se lectable by that
Iine are, in effect, isolated from the central processor. The program wi II be unable to write
information into those cells or read information out from them. On the other hand, if two
se lection Iines are shorted together, information entering or leaving the registers se lectable
by one line will also enter or leave those selectable by the other. In this case, the same information will appear in two different memory cells.
A single address selection failure is not likely to occur by itself. Usually there
will be a pattern of errors appearing throughout the tested portion of memory, which will allow
the operator to isolate the possible sources of trouble. The pattern is most often that of alternating blocks of erroneous and error-free registers.
The following rule of thumb will help the operator track down failing selection
lines: If errors occur in blocks of 1008 registers or more, the trouble lies in the y-axis selection
lines. If errors occur in blocks of 778 registers or fewer, the trouble Iies in the x-ax is lines.

Maindec 703
Page 5
Normally, Maindec 703 will test all of available memory, from register 23 to
the upper limit. There are two ways to restrict the test area. The upper Iimit can be lowered
to exclude one or more memory fields by setting ACS 3 _4 accordingly when the program is read
in. For example, if a PDP-7 has two additional fields for a total memory capacity of 24,576
words, the operator can test only the lower two fields by setting ACS 3 _4 to 1, thus limiting the
test area to the first 16,384 words.
The lower limit can be changed by manually depositing in register 21 a number
one less than the lowest address to be tested. For example, to test only the uppermost memory
field on a machine equipped with 24,576 words, place the quantity 57777 in register 00021 .
This register, labeled LOWT in the program listing, normally contains the number 00021.
Maindec 703 is useful as a rough check of the memory selection networks when
performing routine maintenance tests. It can also be used to confirm an operator's suspic ions
if trouble appears during the normal use of the computer. Sometimes the difficu Ity can be
corrected by the replacement of a module; usually, however, troubles arising from fai lures in
the address selection and memory read-write circuits are likely to require the attention of a
fie Id service engineer.

METHODS
See Discussion, Section 6. 1

FORMAT (Not Applicable)

EXECUTION TIME

The program runs continuously, taking about 75 msec for each 4096 words of
memory, until an error occurs, or until the operator stops the computer. The following table
gives the time required for one pass for each possible memory size.

Memory
Size

Time
(Approximately)

Memory
Size

Time
(Approx imate Iy)

4K
8K
12K
16K

75 msec
150 msec
225 msec
300 msec

20K
24K
28K
32K

375 msec
450 msec
525 msec
600 msec

10.

PROGRAM

10.4

Program listings

Maindec 703
Page 6

10.

PROGRAM

10.4

Program listing

MAINDEC 703: PDP-7 ADDRESS TEST
ITESTS 22-TOP INCLUDING EXTENSIONS.

ENTR,
NEXT,

El ,
El A,
TOP,
LOWT,
LOX,
GO,

CML
LAC LOWT
DAC LOX
ISZ LOX
LAC LOX
SAD TOP
JMP ENTR-l
SNL
DAC I LOX
XOR I LOX
SNA
JMP NEXT
HLT
LAC LOX
HLTISTL
JMP NEXT

ISTART NEW PASS HERE
IINITIALIZE ADDRESS

IMEMORY LIMIT
ILOWER TEST LIMIT
ILOCATION INDEX

•

CAF"
CLOF"
LAsrCLL
XOR HALF"
OAC HALF'
XOR FULL.
OAC LOX
EEM
DZ M I HALF'
DAC I LOX
SAD I HALF
XOR FULL
ADD ONE
DAC TOP
JMP ENTR

HALF,
7777
FULL,
10000
ONE,
1
EEM= 707702
PAUSE GO

IMAl tJ LOOP
I EN D OF MEMORY?

IYES

INO. WRITING THIS PASS?

IY ES.
ICOMPARISON TEST.
IC ( LOX) :C (I LOX)?
IY ES, 1 Fe (AC ) : (1
IERROR: AC SHOWS WRONG BITS AS 1 's
lAC SHOWS ADOH E5S

IMEMORY S I ZER

INO. OF FIELDS FROM AC
ITEST ADDRESS IN LOWER 4K
ITEST ADDRESS IN UPPER 4K
ICLEARS LOC. 7777 IN HIGHEST FIELD
IPUTS AC IN 17777 IN SAME FIELD
IARE THE TWO CELLS DIFFERENT?
INO. MASK OUT 8K BIT.
ITO FORM LIMITING ADDRESS

Maindec 703
Page 7

MAINDEC 703

EEM
ENTR

EIA
FULL
GO
HALF'
LOWT
LOX
NEXT
ONE
TOP
ENTR
NEXT
EI

EtA
TOP

LOWT
LOX
GO
ijALF

FULL
ONE
EEM

PDP-7 ADDRESS TEST

707702
1
14
16

43
23
42
21

22
3
44
20

3
14
t6

20
21
22
23
42
43
44
707702

Maindec 703
Page 8
11 .

DIAGRAMS

11 . 1

Flow Chart

YES