> -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Bruce Griffiths > Sent: Wednesday, February 17, 2010 4:20 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] DMTD to MMTD > > Lux, Jim (337C) wrote: > >>> 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. > >>> > > You've got 8 channels, each zerocrossing at about 200-300 Hz (the > > difference frequency is 123 or 124 > Hz, so you get twice that many zero crossings), or about 1600-2400 > messages/second. At 6 characters > per message, that's about 10,000 characters per second, so you'd need a > fairly fast UART to keep up. > (OTOH, the article mentions dropping characters..) > > > > > A LAN, USB or Firewire interface may be more appropriate all are easy to > implement. > >
Yes, but faster rise times and potentially more EMI. The FTL guys are pretty obsessive about stray noise sources. As far as interfaces.. if I were choosing, I'd use LAN (like pair a Rabbit with the FPGA.. the Rabbit does the UI as a static webserver kind of thing), although USB is ok, but ties the box to one computer. USB is cheaper though. Firewire/1394 is a dying standard... If you need speed, then GigE would probably be a better choice. _______________________________________________ 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.
