First computer with real-time clock?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jul 29 18:47:35 2004

>
> >Hmm. Interesting. That's early 1980s, if not late 1970s, correct?
>
> I have installed in my Altair, a Compu/Time CT-102 real-time-clock
> board which was purchased in 1979. This board supports a battery
> backup option.
>
> This is basically a "digital clock" chip with BCD outputs (intended to
> drive BCD to 7-segment decoders) on an S-100 board. The fact that it
> is a chip intended for a clock display gives rise to certain odd
> characteristics:

The chip used in the HP 98035 (RTC module for the 9825) is even worse.
It's got 7 segment outputs...

IIRC, one of them (d segment?) isn't used, since you can distiguish the
digits without it.The HP microocontroller has to grab the other lines
when each digit strobe becomes active and turn them back into BCD values.
Fortunately this is done in the module, you just send/receive
ASCII-encoded strings to it.

> - To set the time, the software has to "hold down" Fast and Slow time
> set buttons, and watch the time value scroll by until the desired
> setting is reached - just the way a human would set a digital clock
> from that era.

YEs, that's done in the 98035 too. In fact it's just like a digital watch
with one button to select hours/minutes, and a second press for secondes,
and one button for setting (or something like that). Quite fun to watch
the signals when it's 'writing' the time to the battery-backed clock chip.

-tony
Received on Thu Jul 29 2004 - 18:47:35 BST