8085 IO ports

[Tony Duell]

On Sat, Jan 21, 2017 at 4:27 PM, Adrian Graham
<witchy at binarydinosaurs.co.uk> wrote:
> Back to the Executel after a few days relaxing :)
>
> On 17/01/2017 20:59, "Tony Duell" <ard.p850ug1 at gmail.com> wrote:
>
>>> Yep, on the left two. I haven't dared to pull them from the board though
>>> even though they're socketed.
>>
>> Do be careful, the substrate is a brittle ceramic material...
>
> I don't think I'll touch them, they're obviously part of the phone subsystem
> and I doubt I'll ever plug it into a phone line - I have several One Per
> Desks for that sort of thing if needs be.

A telephone line similator is a useful toy to have for something like
this. I have
an old but good one (it use a TMS320 series DSP for signal degredation) that
I bought non working on Ebay. Reseating the socketed chips helped, replacing
a couple of comparators and a voltage regulator fixed it -- the
problem of course
being to find the faulty parts (there are well over 300 ICs in the unit).

[...]

>>> I have, a small 16 channel one that's Saleae Logic compatible so I'm slowly
>>> learning how to drive that too. I should be able to decode addresses and
>>> suchlike using it shouldn't I.
>>
>> Can you clock the analyser from an external input rather than sampling
>> every 10us or whatever? If so, clock it from the Rd/ signal and grab the
>> 16 address lines (8 on the processor pins, 8 on an address latch, most
>> likely a 74LS373, which you will have to find!). Now you can see the
>> sequence of locations that the CPU is reading. Most (but not all) will be
>> instructions. Find one, compare with the listing, see if the sequence makes
>> sense.
>
> I can trigger it on the RD signal yes. There's 2 LS373s which both had dead

Not trigger, but clock. In other words to take a sample on every Rd pulse.

-tony