help - 11/34 console problem - first measurement results

Gooijen, Henk henk.gooijen at
Wed Nov 2 15:00:06 CST 2005

Tony wrote:
> This suggests it is correctly counting the digits you enter (or shifting
> them into a register), but is not displaying them correctly. And it is
> only updating the bottom 8 bits.
> As you probably know, the console is controlled by an 8008
> microprocessor. Of course it's an 8 bit device. Maybe some 'carry' is not
> working correctly.
> What does it do if you press 4 repeatedly? Does it flash the bottom 3 or
> bottom 2 digits? If it's only updating the bottom 8 bits, you see, then
> only 2 digits will flash from 0.
Indeed, pressing the "4" only flashes the last two digits!
How did you know that ?!
Anyway, here are the results of this evening. I write down everything,
so you can read the good and the bad things I found ...
First the BA11K box configuration.
   slot  position   board(s)
     1     A - F    M8266
     2     A - F    M8265
     3     C - D    G7273
     4     A-B C-F  M9312,M7859
     5     C - D    G7273
     6     C - D    G7273
     7     C - D    G7273
     8     C - D    G7273
     9     A-B C-D  M9302,G7273
Next, the response on the display from the keypad. I always
started with pressing "CLR", then repeatedly the same key.
The rightmost (lsb) display is called "A", the one next to it
is called "B", the leftmost (msb) display is called "F".
   button   display reaction (1st time, 2nd, 3rd, etc)
      0    nothing to see
      1    nothing to see
      2    A , B , C , C , C, etc.
      3    A , B , C , C , C, etc.
      4    A , B , B , B , B, etc.    (as Tony predicted!)
      5    A , B , B , B , B, etc.
      6    A , B , C , C , C, etc.
      7    nothing to see
     LSR   SR DISP LED goes on
The LAD, DIS AD, EXAM, and DEP keys seems to give no response.
However, if I pressed LSR, and the SR DISP LED is on, pressing
any key will turn of that LED. Even the CNTRL key ...!
The printset was my lead, so I started from the beginning: the
flat cable from the console to the M7859 module.
All 20 wires check out OK, so one problem source eliminated.
3rd page of the printset.
I checked the +5V and GND faston, and measured a clean 5.15 V.
4th page of the printset.
Here are all keypad switches and the console LEDs connected to
the flat cable. The switches are grouped connected to NAND
gates (8881), and 4 gates are stobed by a signal "READ x H",
where "x" is 1,2,3,4,5. They form a scanned matrix as follows:
signal   |   J1 #6    J1 #7    J1 #8    J1 #9
READ 1 H |   START    BOOT     CONT     HLT/SS
READ 2 H |   CNTRL      3       6        DEP
READ 3 H |    INIT      2       5        EXAM
READ 4 H |     0        1       4         7
READ 5 H |    CLR      LSR     LAD      DIS AD
The "READ x H" signal is derived from the pins 18 (READ 1 H) thru
pin 13 (READ 5 H) on connector J1, via 7404 inverters, and they
all have the following wave form:
             <----  22 msec  ---->
   _____     _____________________
        |    |                    |
        |    |                    |
        |____|                    |__
     -->     <---
         4 ms
I didn't check the timing relation between the "READ x H" signals.
The signals on the combined output of the 8881's have the following
wave form:
            [1]     [2]     [3]     [4]     [5]
   ________     __      __      __      __      __________
          |     | |     | |     | |     | |     |
          |     | |     | |     | |     | |     |
          |_____| |_____| |_____| |_____| |_____|
The number between the square brackets indicates the "READ x H"
signal. So when "BOOT" is pressed the low signal during the time
interval [1] goes logic high. Likewise, when I press the EXAM key
time interval [3] goes logic high.
So, keypad scanning looks OK to me, as the X-Y matrix works fine.
5th page of the printset.
Pin 19 of the connector J1 carries 5,04 V.  That's OK.
This page shows the six 7-segment displays with the 7447 decoder,
the mentioned 7404 inverters for the scanning matrix signal, and
the "DRIVE xL" which are also derived from connector J1, pins 18
thru 13, via a buffer 7417.
Since "READ x H" is OK, I assume that "DRIVE x L" is also OK ...
it must be, otherwise the six 7-segment displays would not be lit !
Last 3 signals are the display values (3-bit) to the 7447 input
A, B, and C. On connector J1 pins 12, 11, and 10 respectively.
As always, the last thing to check should have been the first!
These 3 signals are continously 0 V. That explains why the display
always shows "000000". I can see a short positive pulse when a key
of the keypad is pressed.
This leads me to the following (early) conclusions.
1) the keypad is scanned. All "X" signals of the matrix (READ x H)
   are OK, and all "Y" signals of the matrix (the 8881 outputs) are
   all valid, and give the correct information when a key is pressed.
2) When a key is pressed it is momentarily shown on the display, but
   then the value returns to all zero. I can not see the value, so
   it could be any garbage ...
6th page of the printset.
This shows the component layout of the M7859 module.
Noteworthy is the connector J1, top left. This is the pinning when
viewed at the component side of the module:
   |   #19 . . . . . . . . #1            card edge
   |   #20 . . . . . . . . #2
  card edge
Further, from the diagrams (up till now) I see the the following
pins on J1 (console) are connected to these pins on J1 (M7859).
     J1    --->   J1
 (console)      (M7859)
     20            A      GND
     19            B      +5V
     18            C      SCAN 1 L (READ/DRIVE 1)
     17            D      SCAN 2 L (READ/DRIVE 2)
     16            E      SCAN 3 L (READ/DRIVE 3)
     15            F      SCAN 4 L (READ/DRIVE 4)
     14            H      SCAN 5 L (READ/DRIVE 5)
     13            J      SCAN 6 L (READ/DRIVE 6)
     12            K      NUM 1 H  (A input 7447)
     11            L      NUM 2 H  (B input 7447)
     10            M      NUM 3 H  (C input 7447)
Tomorrow I will dive into the diagram of the M7859 ...
Any hints or comments on this scribbling are welcome !
- Henk.

This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law.  
If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited.  
If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message.  
Thank you for your cooperation.

More information about the cctech mailing list