Re: [rtl] Syncing multiple systems

["C. W. Wright" <wwright@betaweb.com>]

> use an external clock signal. My plan right now is to use some 
> simple electronics and the printer ports on the the machines to get 
> an external interrupt into all the machines, based of course on the 


Hi Theo,

   I used a PIC 16c65a micro-controller to build a GPS synchronized binary
clock which counts 1 hZ pulses from a GPS.  It also uses the leading edge
of the 1 hZ pulse to synchronize internal counters.   We can preset the
chip to any number of seconds ( 32 bits of seconds ) so we can preload it
with the full time and date to the nearest second.  The fractional seconds
counter has a 200ns LSB so we get 24 bits of fractional time as well.  

We've been using the technique for years to keep several airborne data
systems in time-sync with our GPS.   The code could easily be modified to
generate an interrupt to the host computer at some programmed interval or
time-offset if that's what you need.  Initially getting things in sync
must only be done to the one-second level and we use either a networked
time, or manually do it.

The PIC 16c65a sits on the ISA bus nicely.  All you need is address
decoding for the desired address.  The unit has a "slave" data port which
you can connect directly to the lower 8 bits of the ISA bus.   We've got 5
of them on one ISA board with each doing a different function.  

The source for the clock  PIC described above is at: 

  http://aol11.wff.nasa.gov/sra/src/time.asm


Kind regards,

Wayne

wright@osb.wff.nasa.gov
or
wright@web-span.com






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