update: all matrix errors fixed by replacing bad 74LS08 at 6E that was not doing its job of helping select direct / indirect addressing for the matrix processor address selector. That also fixed the spurious 'bad math RAM' error in self test. Still have the divider errors 21-25 and so would still like to understand the math.
On Sep 26, 2013, at 1:40 AM, Douglas Gauck wrote:
> Working on two SW main boards that complain about bad RAM at 5F and 5H even when replaced with known good chips. I think it's elsewhere as they also fail four of the six matrix tests (15, 16, 18 and 20), all the divider tests, and tests A, B, C and D. I would love to know how the math works as shown in the SP-225 Troubleshooting Guide for example:
>
> test 17 (passes) performs (5555-0000) x 4000 = 5555
>
> test 18 (fails) performs (0000-5555) x 0000 = 5555 if you go by the test or (0000-5555) x C000 if you go by the first diagram on page 12
>
> test 19 (passes) performs (2AAA-0000) x 4000 = 2AAA
>
> test 20 (fails) performs (0000-2AAA) x C000 = 2AAA
>
> test C performs ACC = (1B2C-0000) x 4000 + (196A-0000) x 4000 whose result should be 3496
>
> test D performs ACC = (2696-1B2C) x 4000 whose result should be 0B6A
>
> I understand binary and hex but neither is helping me understand how any of the above operations could calculate the way the guide says they do.
>
> Can anyone explain this?
>
> -Douglas
>
> PS. seems my Accumulator seems to hold onto the first value it gets, which is why 17 and 19 pass but 18 and 20 fail with 0000, A with 0001, C with 196A and D with 2696 which is interesting. Test 15 and 16 fail with 1B2C which I can't explain and B ends with 0000.
>
> PPS. Setting bit 8 of the instruction PROMs loads the accumulator, but what does it mean to set bit 9 and 'Road' the accumulator?
> ---------------------------------------------------------------------------
> ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
> ** Please direct other questions, comments, or problems to chris@westnet.com
---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Thu Sep 26 17:27:57 2013
This archive was generated by hypermail 2.1.8 : Thu Sep 26 2013 - 18:50:01 EDT