ISR_Start:
  IF hasCmd = 1 THEN ISR_Exit                   ' exit if holding command
  IF rxCmd = 1 THEN Check_Bit                   ' receiving now?
  IF IR = 1 THEN ISR_Exit                       ' exit if IR line idle

Start_Packet: 
  rxCmd = 1                                     ' set rx flags
  rxBit = 1
  cmdWork = 0                                   ' clear work vars
  bitWidth = 0
  bitCount = 0
  GOTO ISR_Exit

Check_Bit:
  IF IR = 0 THEN Update_BitWidth                ' still in bit?
  IF rxBit = 0 THEN ISR_Exit                    ' in idle period?
  rxBit = 0                                     ' no, clear bit flag
  IF bitCount > 0 THEN Test_DBit                ' start or data bit?

Test_SBit:
  IF bitWidth > 74 THEN Next_Bit                ' proper start bit?
  rxCmd = 0                                     ' no, reset
  GOTO ISR_Exit

Test_DBit:
  cmdWork = cmdWork >> 1                        ' prep for next bit
  IF bitWidth < 34 THEN Next_Bit                ' "1" bit?
  cmdWork.6 = 1                                 ' yes, set it

Next_Bit: 
  bitWidth = 0                                  ' clear for next bit
  INC bitCount                                  ' update count
  IF bitCount < 8 THEN ISR_Exit                 ' done?
  hasCmd = 1                                    ' set available flag
  cmdCode = cmdWork                             ' copy work to output
  rxCmd = 0                                     ' clear rx flag
  GOTO ISR_Exit

Update_BitWidth: 
  INC bitWidth                                  ' else inc width
  rxBit = 1                                     ' refresh in bit flag

ISR_Exit:
  RETURNINT 104                                 ' 26 uS @ 4 MHz 