[Techtoolslist] Logic analysis and the Atari Test connector?

Wed May 24 17:48:02 EDT 2023

In preparation for this I was looking at the missile command source code
from https://6502disassembly.com/va-missile-command/ looking at the reset
vector and how the self test is started:
And looking over the self test it (at a high level)
Starts the pokey growling
Lights player 1 start light (which I don't have connected on the test bench)
Reads the inputs port (0x4900) and watches for the VBLANK signal, spinning
until it sees it.
Feed the watchdog
Change the poke sound to a "pure tone and lower volume"
Test the zero page and stack ram

This got me thinking, I am never hearing anything but the growl, so I let it
run in self test for a minute, then use the 9010 to read some zero page
values, all 0.... Hmm, so its not getting to the memory test.

Used the 9010 to read 0x4900 and it is always returning BF, which doesn't
make sense as the vblank should be causing it to change (and the self test
switch does change it so the read is working).

The screen looks fine so the VBLANK is working.

Tossed my HP logic comparator onto the 244 used to read the inputs and it
reported pin 9 bad (which happens to be the pin that VBLANK is read
through).

Piggybacked a new 244 and self test started up fine, and game mode works.

So it was all stalled on waiting for that vblank test which wasn't coming
through.

Still going to look at setting up the LA on the connector for future use but
this one is fixed.

David

-----Original Message-----
From: Techtoolslist <techtoolslist-bounces at flippers.com> On Behalf Of Alex
Yeckley
Sent: Wednesday, May 24, 2023 1:35 PM
To: Technical Tools Mail List <techtoolslist at flippers.com>
Subject: Re: [Techtoolslist] Logic analysis and the Atari Test connector?

One of the main reasons for my take on this is that I almost always needed
to monitor a signal (such as the CPU clock) that wasn't brought out to the
card edge.  I suppose if you add some sort of flying probe connection then
the edge might be more useful.

You'll also need to reverse-engineer at least some portions of the code, if
you haven't already.  I'm guessing you knew that.

-----Original Message-----
From: Techtoolslist <techtoolslist-bounces at flippers.com> On Behalf Of
davids at oz.net
Sent: Wednesday, May 24, 2023 4:30 PM
To: 'Technical Tools Mail List' <techtoolslist at flippers.com>
Subject: Re: [Techtoolslist] Logic analysis and the Atari Test connector?

I have replaced all sockets on the board (rom, prom, and CPU). So that isn't
a problem.

-----Original Message-----
From: Techtoolslist <techtoolslist-bounces at flippers.com> On Behalf Of Alex
Yeckley
Sent: Wednesday, May 24, 2023 1:16 PM
To: Technical Tools Mail List <techtoolslist at flippers.com>
Subject: Re: [Techtoolslist] Logic analysis and the Atari Test connector?

I have used both approaches.  The "glomper clip" approach worked out better
for me, but usually required replacing the original CPU socket first.  YMMV.

-----Original Message-----
From: Techtoolslist <techtoolslist-bounces at flippers.com> On Behalf Of
davids at oz.net
Sent: Wednesday, May 24, 2023 3:59 PM
To: Technical Tools Mail List <techtoolslist at flippers.com>
Subject: [Techtoolslist] Logic analysis and the Atari Test connector?

I have a missile command board which using the fluke 9010 passes all memory
and rom tests perfectly.  Also can exercise the pokey with no problem.

But when I try to go to UUT the game just starts to make an explosionish
sound and then watchdogs.   Game mode and test mode.

Verified the WD is working correctly.

So my next thought was to connect the 16702B to the CPU address and data
lines and see if I could figure out where the startup goes off the rails.
Not supper excited about having to use the test clips on 16 bits of address,
8 bits of data and misc other signals.

Realizing there is that nice juicy edge connector right next to the CPU I
was thinking about having an adapter board made that would have and edge
card and then a set of pod connectors that I could just plug the pod cables
into directly.

Am I reinventing the wheel here?  Anyone done this and have any gotchas to
mention?

Or am I over thinking this and should just get a 40 pin glomper clip and
attach to the top of the CPU? And connect to that?

David

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