#include P18F458.inc
	
RAM_ADDR	EQU 40H	
COUNTREG	EQU 0x20	
CNTVAL	EQU 4		
CNTVAL1	EQU 5		
				
	ORG	0
	CALL	COPY_DATA
	CALL	CAL_CHKSUM
	CALL	TEST_CHKSUM
	BRA	$
COPY_DATA
	MOVLW	low(MYBYTE)		
	MOVWF	TBLPTRL		
	MOVLW	hi(MYBYTE)		
	MOVWF	TBLPTRH		
	MOVLW upper(MYBYTE)	
	MOVWF	TBLPRTRU		
	LFSR	0,RAM_ADDR		
C1	TBLRD*+			
	MOVF	TABLAT,W		
	BZ	EXIT			
	MOVWF	POSTINC0		
	BRA 	C1
EXIT	RETURN
CAL_CHKSUM
	MOVLW	CNTVAL		
	MOVWF	COUNTREG		
	LFSR	0,RAM_ADDR		
	CLRF	WREG
C2	ADDWF	POSTINC0,W		
	DECF	COUNTREG,F		
	BNZ 	C2			
	XORLW	0xFF			
	ADDLW	1			
	MOVWF	POSTINC0
	RETURN
TEST_CHKSUM
	MOVLW	CNTVAL1		
	MOVWF	COUNTREG		
	CLRF	TRISB			
	LFSR	0,RAM_ADDR		
	CLRF	WREG
C3	ADDWF	POSTINC0,W		
	DECF	COUNTREG,F		
	BNZ 	C3			
	XORLW	0x0			
	BZ	G_1			
	MOVLW	'B'
	MOVWF	PORTB			
	RETURN
G_1	MOVLW	'G'
	MOVWF	PORTB			
	RETURN
	ORG 0x500
MYBYTE DB 0x25, 0x62, 0x3F, 0x52, 0x00
	END