help - 11/34 console problem - first measurement results - test-drb@ccmp.vtda.org

6 Nov 2005

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Subject: RE: help - 11/34 console problem - first measurement results
   From: "Gooijen, Henk" <henk.gooijen at oce.com>
   Date: Sun, 06 Nov 2005 09:20:27 +0100
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

Content-Transfer-Encoding: quoted-printable

Tony wrote:

  Interesting, the LSB is being lost somewhere
(that would explain why
 1 does nothing, why 5 behaves as 4, etc).

 What sort of RAM is on this board (I can't be bothered to find the
 prints tonight ;-)), do you know if it's good. I've found old SRAM
 to be notoriously unreliable.  =

Interesting, I had not thought of that, may be a stuck bit.
I must have a better look at the program code listing. Checking out
the RAM is a bit difficult. It consists of two 4-bit chips with
separate data IN and data OUT pins, type 86586 (?).
If the 8008 uses the RAM for storage of variables, I guess that I can
safely say that the RAM (plus associated circuitry to read/write) must
be OK.

  Since I have a logic analyser 'to hand',
I would start looking at those
 3 inputs to the '47. Where do they come from on the M7859? An output
 port on the 8008? Do we know that port is latching correctly? Or more
 likely, the 8008 is writing the wrong values to it. 
 = 
I'd consider that the 8008 is getting bad input data from a bad scan line
which it will output or that it's outputing correctly and the data is 
corrupted after output due to bad latch or other hardware.

...
 Page KY-4 has all the decode logic. There is a second
post to this list
on its way, posted Friday morning ... it's now Sunday morning ...
The signal KY4 READ INPUT 5L from the 74154 is used on page KY-3 to
enable 8093 AND gates to read the scan matrix lines. =

The signal KY4 LD REG 0H via a 7404 from the 74154 is used on page KY-6
to enable a 74175 latch of which the outputs drive the scan matrix.
Likewise, KY4 LD REG 1H drives the 3 NUM lines for the 7447.
 =

Before I go on writing long stories here, I think it is best to wait
for the e-mail from last Friday to appear here.
Thanks for working with me Tony, it helps keeping focussed ...
 =

- Henk, PA8PDP. 
One likely possibility is not ram as a prblem but a I/O port that has a
stuck bit. Or the control for that port is stuck.  This is most likely
if the basic fuctions are there (8008 program runs) but some parts of
the data used to control the 11/34 or display it's status is not correct.

FYI the 8008 can be single stepped if you pull the "READY" line each 
cycle and just look at the bus with a simple logic probe or clip.

Allison