21 Dec
2016
21 Dec
'16
8:45 p.m.
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:
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.
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.