"Peter L. Peres" wrote:
>
> On Sat, 19 Oct 2002, Robert Rolf wrote:
>
> *>Been there, done that, and found that a RTC chip like the DS1302
> *>just makes a LOT more sense, if you can pursue that option. 3 pins (2 of
> *>which you can share with other functions if you're clever) and a
> *>energy source (MnO, Li or supercap) gets you a hassle free solution.
>
> Me too except I prefer to use a 12C508A as timekeeper (with 32kHz xtal).

But will it run for months unpowered? What current did you get down to?
The DS1302Z osc draws around 300nA (so low I had a bugger of
a time measuring it) which means you get nearly shelf life
with a tiny lithium and months on a rechargable MnO battery (3v).

And the DS1302 also has 31 bytes of RAM that can be used to store
system state and data.

Whatever works for you given your constraints...

R

> It sends 600Baud TTL level RS232 data on a pin (using open drain drive to
> avoid loading the supply). The setting is done using two buttons (time
> honored shift & set) which can be wired to another cpu is necessary. The
> timer runs in packed BCD. The 300Baud tx does most of the constant run
> time timing ;-) ;-) Getting the years to work right took some work, but I
> do not need years usually.
>
> The tx format is HHMMSSDDMMYYYY in packed BCD (7 characters per second).
>
> Some RTC chips (from Seiko etc) operate like this but use 3 wire format.
> They also use 2 set buttons as above.
>
> Peter

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