Mystery 8085-related IC identification needed please
hilpert at cs.ubc.ca
Wed Dec 21 14:45:11 CST 2016
On 2016-Dec-21, at 11:44 AM, Tony Duell wrote:
> On Wed, Dec 21, 2016 at 7:37 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
>> The counters may be the beginning of a video timing divider chain or a clock divider for the LUCY chip.
>> (e.g. a diagram in the document you mentioned shows a div-6 between a 6MHz crystal osc and the LUCY chip.
>> The division factor may vary of course in the executel depending on the crystal.)
>> Also to keep in mind as you trace it out, 749x counters were often used with gates between the
>> outputs and reset inputs to change the count modulus / division factor.
> I seem to remember Adrian said that the reset pins on these counters (assuming
> they are 7492s, and those pins are reset) come from an inverted version of
> the 8085 reset. I think it's unlikely that the 8085 will be
> continually reset, so
> I would think the counters were not reset by a combnation of their outputs.
He did mention they (pins 6,7 and 8085 reset) were in association with a 7414 but it wasn't entirely clear or ensured they were part of the same logic path as opposed to merely using separate inverters in the same chip. Timing divider chains typically don't need to be reset in sync with the system microproc, so there's the possibility, if not likelihood, they're logically unrelated; hence modulus alteration is something to keep in mind.
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