;
;	Example program #1 for use with the OATLEY Electronics PICAXE Development System
;
;	This program is an example of using a UHF Receiver to receive 3 bytes of data
;
;	Author		Jeff Monegal
;
;	Microcontroller	PICAXE 18X
;
;	Compile date	28/3/2010
;
;--------------------------------------------------------------------------------------------------
;
;	NOTES
;
;--------------------------------------------------------------------------------------------------
;
;	The 3 bytes of data to be transmitted are contained in the 3 byte registers. The checksum
; value is first calculated by exclusivly ORing byte_1 with byte_2. The result is stored in the
; checksum register which is then placed on the end of the data frame to be sent. A checksum is
; used to ensure that the received data is as error free as possible. At the receiver the checksum
; is compared with the result of exclusively OR ing the same 2 registers.
;
;--------------------------------------------------------------------------------------------------

symbol	byte_1 = b2
symbol	byte_2 = b3
symbol	byte_3 = b4
symbol	checksum = b5
symbol	rx_checksum = b6

symbol	led = 7

;--------------------------------------------------------------------------------------------------
;
;	Here the received data frame comes in on pin 7. The PICAXE stores the data in the defined 
; registers. Next the same 2 bytes are XOred to get a calculated RX checksum. Last this checksum
; value is checked against the TX calculated checksum. If the data frame was received succesfully
; then the 2 checksum values will be the same.
	
start:
	
	serin 7,t2400,("code"),byte_1,byte_2,byte_3,checksum	;receive 4 bytes on pin7 
	
	rx_checksum = byte_1 xor byte_3				;calculate rx checksum
	if checksum <> rx_checksum then data_error		;compare calculated checksum against rx'ed checksum 
	high led						;turn on led to say data received OK

;	User program goes in here	
;	The 3 data bytes can be used for what ever the programmer wants 
;	
	goto start

data_error:

	byte_1 = 0
	byte_2 = 0
	byte_3 = 0
	low led
	goto start
	
;	The routine is exited with the 3 bytes of data stored in the 3 byte registers. If there was 
; a checksum error the software ignors the 3 data bytes and exits the routine with the 3 data bytes
; all clear. To other parts of the program this will indicate the frame was not received correctly.
;
;	It is also important to note that although only byte_1 and byte_3 have been used in the checksum
; calculations, any of the 3 bytes could have been used and even all 3 bytes could be used.