HP98035 Real Time clock and AC5954N clock chip

[CuriousMarc]

>The clock chip seems to be a normal digital watch/clock chip. The inputs to
>it are essentially the 'set' buttons, the outputs are the 7 segment lines and
>digit strobes. But I have not found a data sheet on it anywhere.
Tony, looks like you are absolutely right, this would be a garden variety digital clock chip! Looking at the schematics, U15:
https://drive.google.com/open?id=1kNq0-IUBcPKDAE8k4Ztg2eoUCWHPr4hI
The outputs Sa-Sg are standard names for 7-segments, and are read on the processor bus. They don't bother to read segment d, I suppose they can differentiate all the numbers without reading that one. DI must be the Decimal Indicate segment. D1-D3 would be the digit counter. C25, READ and SET are the inputs - we'd have to find what they exactly do. Would they then set the clock by just toggling the digits in one by one as one would do to reset a clock? Anyhow, it seems I could set the Sa-Sg signal to test pattern and see if indeed I read digits different than 8, and confirm that everything is working but the clock chip. Now, how to find a more or less equivalent replacement chip.
Marc


-----Original Message-----
From: Tony Duell [mailto:ard.p850ug1 at gmail.com] 
Sent: Thursday, June 06, 2019 8:25 PM
To: CuriousMarc; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: HP98035 Real Time clock and AC5954N clock chip

On Thu, Jun 6, 2019 at 8:57 PM CuriousMarc via cctalk
<cctalk at classiccmp.org> wrote:
>
> All HP fans in general and Tony in particular,
> I have the exact same problem. HP98035 real time clock module
> (http://hpmuseum.net/display_item.php?hw=168), plugged into a HP9825T
> (http://hpmuseum.net/display_item.php?hw=171), accepts commands, reads back
> all 8's. Battery is new, is charging and at the correct voltage.
> Documentation says "never run the module without the battery or it would
> damage the AC5954N clock chip". When I got the module it had not battery in
> it, so this is what could have happened. Tony, did you eventually repair
> your module or find some data on the clock chip?

I've certainly got a working 98035, but I can't remember if I repaired this one.

The clock chip seems to be a normal digital watch/clock chip. The inputs to
it are essentially the 'set' buttons, the outputs are the 7 segment lines and
digit strobes. But I have not found a data sheet on it anywhere.

-tony