Table of Contents
Advertisement
SAR
Bits
9
10
11
12
13
14
RD
WR
1
0
1
,-------,
I
I
I
I
I
*DVR
I
I
I
~
X-Decode ALD Representation
SAR
Bits
2
3
4
5
6
7
8
RD
WR
l
0
1
1 - - - - - - ,
I
I
I
*DVR
I
I
:
~
Y-Decode ALD Representation
Figure 1-123..
X and Y Decode Drivers
X-Decode:
The X-decode drivers use storage
address register bits 1 and 9 tc 14..
Three
syrrbols are used in the ALDs to show the
ccnditicns necessary to activate a decode
driver.
They are:
1:
0:
This bit is not used to ccntrol this
driver ..
This bit roust be present in order to
activate this driver.
This bit roust not be Fresent in
order to activate this driver.
Therefore, the S-decode driver Sfecified
in Figure 1-118 is activated when bit 12 of
the storage address register is on. bit 13
of SAR is off, and tit 14 of SAR is on.
The status of bits 9, 10 and 11 will not
affect this driver ..
Y-Derode:
The Y-decoae drivers use SAR
bi ts 2 to 8 and are shown in the AL:Cs in
the same way as the X-decode drivers ..
Therefore, a Y-decode driver SFecified
as
in Figure 1-118 is activated when SAR bits
3 and 6 are on and bits 7 and 8 are off ..
Bits 2. 4 and 5 will not affect this
driver.
1.25 .. 2 SCOPING STORAGE
Use an oscilloscope with a 25- tc 60-
nanoseccnd rise-time.
The DuMont 766H the
1-130
(7/69)
Tektronix* 561 S and 453 are oscilloscopes
that meet these SFecificaticns.
Use the
oscilloscope probe ground near the point
being probed.
Use read-call 01 C-B2A3D11
for an oscilloscope sync point.
1.25.2.1 Scoping X and Y Source-Terminating
Resistors
When storage problems cannot be easily
diagnosed from the console by card
substitution, scoping the X and Y
terminating resistors may provide
information that will assist in locating
the troul:le.
When a failure is common to a
large block of storage and cannot be easily
isolated to a particular X- or Y-line,
scoping the X and Y terminating resistor,
while using the Medel 25 diagnostic scan
functions CMDM starting at Diagram 1-100),
may indicate where the trcuble might be
found ..
Because of SLT packaging, and because
the array plugs into an SLT large board, a
current probe can be used in very few
places to check or observe the drive
currents.
However, all X and Y drive
current comes f rorr a grcuF of four
resistors, two for the X-lines Cone for
read and one for write) and similarly for
the Y-lines.
The resisters are mounted on
the swing-open side of the store gate and
are connected to the current sources via
twisted wire cabling.
An indirect indication of array current
is possible by rroni taring any of the yellow
wires (for example, the yellow wire to pin
U4B12 for Y read current).
If a current
probe is available this can be done
directly on the back panel, or
al terna ti vely with a voltage :r;robe always
on the yellow side connection of the
resistors; the latter method will require
the opening of the resistor gate (Figure
1-124).
Figures 1-125 through 1-130 show the
waveforms for rrai
n
storage control and
drive lines during a specific condition.
A variety of situations is represented by
these oscilloscope photografhs.
Because
these waveforms will occur only when a
specific address er grcu:r: of addresses is
accessed, they will be mixed in with nany
correct waveforms.
Under these conditions
they can be difficult tc distinguish from
incorrect patterns..
An attempt should be
made to locate the failing addressees) and
put the 2025 into an address loop while
scoping is perforrred.
Refer to Chapter 2.
* Trademark of Tektronix, Inc.
Advertisement
Table of Contents
