I've used both Manchester and MFM techniques. Of these, the MFM was=20 by far the easiest to implement. My MFM protocol uses 25% duty cycle pulse as a logic zero and a 75%=20 duty cycle pulse as a logic one. My normal protocol uses a period of=20 no data as the strobe (load) signal. That is: a retriggerable timer=20 keeps being reset while data is being received. When the timer=20 expires, the current data packet is accepted as complete. The protocol originated from way back in the '80s when I was sending=20 bit-mapped 7 segment data to remote LED displays. This was all CMOS=20 logic - no fancy micro anywhere in sight. I just carried the=20 protocol along as I went from CMOS logic to Motorola 680x / hc11, then to P= ICs. The downside is that the bandwidth required is about double that of=20 Manchester encoding. For the slow, wired or optical bitstreams that=20 I frequently use, its simply not a problem. Like Manchester encoding, MFM is tolerant of bit rate errors. A=20 logic zero can increase its pulse width to almost the 50% point=20 without error, a logic one can decrease its pulse width to almost 50%=20 without error. This has allowed simple (and inexpensive) RC clock=20 and timing networks in my very early designs. Note that the protocol is not limited to byte-sized packets. The=20 early bit-mapped 7-segment data I started using this with used 32 bit=20 packets at about 500 bits/sec, the Pyro control system we used to=20 manufacture (and still being used to this day) uses 160 bit packets @=20 25K bits/sec, the rectifier monitoring system we build for Dow=20 Chemical uses 25 bit packets @ 4096 bits/sec. The Dow stuff used to=20 be implemented in 16-macrocell PLDs (Intel 5C060 / Altera EP610) but=20 are now done with 16F676 PICs. dwayne At 03:55 AM 8/16/2011, Forrest Christian wrote: >I'm in the process of defining the protocol to be used from some 'local >area' sensors to a PIC processor. In short, this will be PIC-to-PIC >communication over a one-way optoisolated interface. --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .