Simon Nield [simon.nield at QUANTEL.COM] says:
I need to biphase code a byte for serial transmission over an rf link. In other words each '1' becomes '10' and each '0' becomes '01'. If it makes the code easier then '1' becoming '01' and '0' becoming '10' is ok too.
this _could_ be done with a lookup table, which would be fast, but that's not the point of a tiny code challenge now is it ?
Here's a chunk of code that does the job.; data starts off stored in lo_int_temp+0 ; program_status(fRFToggle) flips each time around the loop to select which nibble we are attacking btfss program_status, fRFToggle swapf lo_int_temp+0, F ; select the appropriate nibble ; biphase code bit movlw b'01010101' ; start biphase coding... btfsc lo_int_temp+0, 0 addlw b'00000001' ; if bit 0 is set then W = 01010110 btfsc lo_int_temp+0, 1 addlw b'00000100' ; if bit 1 is set then W = 010110xx btfsc lo_int_temp+0, 2 addlw b'00010000' ; if bit 2 is set then W = 0110xxxx btfsc lo_int_temp+0, 3 addlw b'01000000' ; xxxxabcd now encoded as aAbBcCdD, where A = !a ; exits with a coded version of the relevant nibble of lo_int_temp+0 in W happy hunting, Simon
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<A HREF="http://www.piclist.com/techref/microchip/manchester.htm"> PIC RF IO - Manchester Encoding</A>
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