16 Dec
2016
16 Dec
'16
6:51 p.m.
If one of the 749X parts, one should be able to figure
it out by looking at the NC pins. The different chips look to
have different NC pins. If something is connected to one
for one of them, it would most likely be one of the others.
Dwight
________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Tony Duell
<ard.p850ug1 at gmail.com>
Sent: Friday, December 16, 2016 10:25:21 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Mystery 8085-related IC identification needed please
On Fri, Dec 16, 2016 at 6:19 PM, Peter Coghlan <cctalk at beyondthepale.ie> wrote:
And IIRC pins 6 and 7 are reset _inputs_ on the 74x90 (I don't have the
pinouts to hand, what about the 74x92 or more likely 74x93?). But active
high, not active low. So it's possible the reset signal comes from elsewhere,
resets these counters (as some kind of clock divider chain) and is inverted
by that '14 to feed the 8085 reset input.
I doubt it's a uA733. I can think of no logical reason to have one of those
in this sort of circuit.
-tony
They aren't 'standard' 14-pin DIPs in that they don't follow the
GND-on-pin-7-Vcc-on-pin-14 layout. Pins 6 and 7 on both are wired together
(not to GND) and form the RESET signal for the 8085 via the 7414 at 10A,
source for this signal is unknown currently. Pin 5 on both appears to be Vcc
and pin 10 is GND or at least are pulled high and low respectively.
Could they be 74(LS)90? Those have Vcc on pin 5 and GND on pin 10.