Here's a simple set of manchester encode/decode routines.
Code:
inbyte	VAR	BYTE
outword	VAR	WORD
inword	VAR	WORD
outbyte	VAR	BYTE
i	VAR	BYTE

Begin:
    CLEAR
    inbyte = 12	       ' byte for test
    GoSub Encode       ' convert to Manchester word
    inword = outword
    GoSub Decode       ' convert from Manchester word
    outbyte = 0
    goto begin
    
Encode:
	For i = 0 to 7 ' loop for 8-bits
	  outword.0[(i*2)] = ~inbyte.0[i] ' Get bit value for bits 0,2,4,6,8,10,14 in outword
	  outword.0[(i*2)+1] = inbyte.0[i]' Get bit value for bits 1,3,5,7,9,11,13,15 in outword
  	Next i  ' 
Return

Decode::
	For i = 0 to 7			' loop for 8-bits
	  outbyte.0[i] = ~inword.0[i<<1]	' outbyte bits 0-7 = inword bits 0,2,4,6,8,10,14
	Next i  ' Inverts each 2nd bit position in inword I.E. 01 = 0, 10 = 1
Return