Hi Any of the Cyclone III parts will do the FPGA part without breaking a sweat. That includes the FIFO and ASCII stuff. I agree that the "magic" is in the zero crossing stuff.
Bob On Feb 17, 2010, at 6:34 PM, Lux, Jim (337C) wrote: > >> -----Original Message----- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf Of Bruce Griffiths >> Sent: Wednesday, February 17, 2010 2:10 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] DMTD to MMTD >> >> The latest version actually records time stamps from a continuously >> running counter clocked at some at a constant frequency (100Mhz??)for >> all channels simultaneously. >> They may use a flag bit for each for each channel to indicate to which >> channel or channels the zero crossing time stamp belongs. > > Simpler than that.. it grabs 20 bit numbers and shoves them out in ASCII over > a com port with an indication of which channel it was for. > The FPGA has a 20 bit free running counter at 100 MHz. When an input changes > state, it latches the counter, and shoves it out along with the channel > number. They use an offset frequency >100 Hz so that you don't have to > disambiguate the counter rollovers. (20 bits rolls over every 10+milliseconds > counting at 100 MHz) > > I don't know if there's a FIFO in front of the UART (e.g. what if you get > simultaneous zero crossings).. but I would expect there is. > > The "hard work" is in the zero crossing detector ahead of the FPGA. (and > perhaps in the latching of the ZCD inputs into the FPGA). > > Given how long ago it was made, that FPGA isn't a huge one. > > _______________________________________________ > 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. > _______________________________________________ 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.
