Real-Time Clock

Real-Time Clock

Post by antonino micel » Wed, 12 Apr 2000 04:00:00



Hello,

We are planning to use a PC/104 embedded cpu  for
a project and we need to be able to sync our clock
with an external clock. I know that most boards come
with the MC146818 CMOS RTC, but from the data sheet,
it indicates that smallest unit of time that it will handle
is the second. Is there true? If so, how can keep time to the
millisecond level? Do I need to buy a separate time/counter circuit
with a crystal osciallator? I have a 1 Hz GPS pulse train
with very precise edges.

Thanks,
~Anthony

 
 
 

Real-Time Clock

Post by Ian St. Joh » Thu, 13 Apr 2000 04:00:00


Use the 'periodic interrupt' feature for a 1024/sec interrupt rate to
increment a counter. Irq for RTC is 8. Period can be adjusted to 2048, 4096
or 8192/sec Anything over 2k/sec is sometimes erratic if the RTC is actually
implemented in the VLSI glue logic chips, as these are often not tested for
functionality in this area.

Note: Look up MXCO ( microprocessor controlled crystal oscillator ) as a
possible option. They were working on commercializing them last I looked.
They include provisions for a 1 pps GPS sync signal lock.


Quote:> Hello,

> We are planning to use a PC/104 embedded cpu  for
> a project and we need to be able to sync our clock
> with an external clock. I know that most boards come
> with the MC146818 CMOS RTC, but from the data sheet,
> it indicates that smallest unit of time that it will handle
> is the second. Is there true? If so, how can keep time to the
> millisecond level? Do I need to buy a separate time/counter circuit
> with a crystal osciallator? I have a 1 Hz GPS pulse train
> with very precise edges.

> Thanks,
> ~Anthony


 
 
 

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