HP98035 Real Time clock and AC5954N clock chip

[Tony Duell]

On Fri, Jun 7, 2019 at 6:50 PM CuriousMarc <curiousmarc3 at gmail.com> wrote:
>
> >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.
>

I wondered if it's actually a digtal watch chip (2.5V could have been a couple
of mercury cells in series, LED watches were not uncommon back then).

In which case it would not normally have come in a 0.6" wide DIP. Perhaps
normally it was a bare chip directly mounted on the watch circuit board or
something.

The DIP version would be unusual, which is perhaps why we can't find data
on it.

-tony