ComputerVoltageSources

While running an errand, it dawned on me that rather than just 
synchronize the clocks, I could determine the error and adjust the 
timer to dial in the slave's frequency.  I normally use a gra of 2000 
which divides the ~2 MHz timer input for a 1 mS interrupt.  If the 
slave clock is slower, then I decrease gra to increase the clock, and 
the reverse if the slave clock is faster.  I display the current gra 
value on my LCD and it varies between 2001 and 2002 so it doesn't make 
much difference.  When I disconnect the synchronization, the two do 
drift apart slower.

My real-time clock just increments a long variable so it will wrap 
around to 0 every 49 days.  It depends on how the code is written, but 
it is pretty simple to calculate delays.  For example, to set the Aux 
output high in 20 mS, I simply compute a future time value such as 
turn_off=time_count+19.

Then, either in the interrupt routine, or in main code, I set Aux low 
when time_count>turn_off.  The timing may be off by less than a mS 
from my time_count due to latency, but errors never accumulate. 

Dave


--- In ComputerVoltageSources@yahoogroups.com, "djbrow54" <davebr@...> 
> Alt 2:  I setup both modules using 1 mS timer interrupts.  I sent a 
> $fe midi active sense every 256 mS to synchronize the two clocks.  I 
> output a periodic 1 mS clock and there is some minor jitter but the 
> modules stay synchronized.  I put a .wmv video in the 
> Files>BasicAtomPro>Original PSIM>Dave Brown folder showing the 
> results.