On Sat, Apr 12, 2014 at 9:48 AM, Magnus Danielson < mag...@rubidium.dyndns.org> wrote:
> > In fact a 5 bit counter is enough, and then a '373 to sample it. The > enable to the 373 needs to be synchronous to the 5/10 MHz clock, so a pair > of DFFs ('74) is needed to synchronize the PPS and another pair to create > the single cycle enable. > > It turns out all of this is built into the AVR chip. There is a counter and logic to copy the current counter value to a register on a PPS pulse raising edge. The counter keeps running and every second its value is trapped. I can connect the OCXO and the PPS directly to the AVR pin. The AVR has hardware (a fast comparator) to "square" a low amplitude sine wave and trap the counter on a zero crossing. So it looks like I can get rid of ALL of the external chips. The built in DAC is working well also but it needs some external resisters and caps. No need for '74 FFs or '373' or counter chips. I do get precision timing with no time critical software, no 74xxx chips. -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.