Michael,

For further discussion, I'll refer to the physical layer (i.e., the layer having the 4B/5B NRZI encoding for RF, or NRZ for UART output) as PHY, the data link protocol layer (i.e., an HDLC class of procedures) as DLP, and the upper layer protocol (e.g., the RPC layer) as ULP. That said...

"a) Have you implemented this protocol in assembler or in C ?"

C for all of the ULP and DLP implementations. The vast majority of PHY implementations have been in C. Only with high data rates and when I could not use MCU timer assist, have I had to resort to assembly.

"b) Have you done an implementation on an 8051 or derivative part ?"

I use the ULP and DLP, which are mostly independent of the PHY layer, on all sorts of MCU's, 8051 derivatives included. The PHY layers of the 8051 projects thus far have been UART/RS-232, UART/RS-422, and UART/IrDA(SIR). For whatever reason (mostly client selected the MCU), all of the RF PHY projects have been implemented on PIC's in all ranges 12', 16', and 18' series.

"c) When you implemented it on an embedded platform how did you implement the serial protocol? In a special chip? FPGA? MPU timer code? or specialized UART mode?"

All implementations have been entirely in the MCU without using the UART. Whether or not I have used the MCU's timer facilities has been entirely based on the existence of suitable timer functionality. The majority of implementations use a timer with capture and compare capability for receiver/transceiver or a timer with compare for transmit only. For the really low-end devices, or when the data rate is too close the the instruction execution rate, I have not used any timer, instead counting instruction cycles (ugh!).

"d) Are you in a position that you could or would want to share code for this? It would make a nice addition to the 8052.com code library."

Most of this stuff is "Dan Henry's Background Technology" in my Bag-O-Tricks, as opposed to client-owned, so I could share it. I will give serious consideration to doing so. It might take a little time for me to get in a form that is fit for human consumption. Since the ULP and DLP is more or less standard stuff, should I take it that you are more interested in the PHY layer specifically for RF, or are you interested in the whole kit-and-caboodle (ULP/DLP/PHY)?