Mystery 8085-related IC identification needed please

Adrian Graham witchy at
Sat Dec 17 08:02:44 CST 2016

On 16/12/2016 18:25, "Tony Duell" <ard.p850ug1 at> wrote:

> On Fri, Dec 16, 2016 at 6:19 PM, Peter Coghlan <cctalk at>
> wrote:
>>> 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.
> 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.

Thanks all, the pinouts are matching the LS9x counters so I just need to
trace more lines to hopefully narrow it down. Pins 6 and 7 are definitely
inputs so you're right Tony, the reset must come from elsewhere. One of the
outputs is confusing though since it appears to come FROM 5V via a resistor,
I can't see anything in the datasheets that hints it may also be used as an
input or that pulling it high affects behaviour. Maybe I mistraced in
tiredness the other night.

Back to the DMM then!

Cheers folks :D

Binary Dinosaurs creator/curator - the UK's biggest private home computer

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