Byte 1: Recipient
Byte 2: Sender
Bytes 3-n: Payload
Byte n: Checksum

Byte 0: Constant Sync value (magic number)
Byte 1: Recipient
Byte 2: Sender
Bytes 3-24: Payload
Byte 25: byte of 1st flipped bits
Byte 26: byte of 2nd flipped bits
Byte 27: byte of 3rd flipped bits
Byte 28: checksum

transmit:
  cjne R1,#CHECKSUM_POINTER,notxe
    sjmp endtxdf ;end operations if we reached checksum pointer
  notxe:
  inc R1 ;Process next value (first value printed in triggering function)
  mov A,@R1
  cjne A,#SYNCVAL,tsync
    xrl A,#0FFh ;Next value is the magic number so carry is cleared and flip the byte
    sjmp etsync
  tsync:
    setb C ;Next value isn't magic number so carry is set
  etsync:
  mov SBUF,A ;Send value out on serial line
  ;then move carry into 24-bit value (bytes 25 through 27)
  mov A,byte_25
    rrc A
  mov byte_25,A
  mov A,byte_26
    rrc A
  mov byte_26,A
  mov A,byte_27
    rrc A
  mov byte_27,A
  endtxdf:
  ;transmit interrupt ends
reti