; define variables
adtable EQU 0x39 	; adc result table 8 bytes
chan 	EQU 0x41 	; channel no
val 	EQU 0x42 	; word size adc result variable
oldb 	EQU 0x44 	; last portb value
char 	EQU 0x45 	; single character command
command EQU 0x46 	; upper 4 bits of command
n 	EQU 0x47 	; lower 4 bits of command
m 	EQU 0x48 	; byte size temporary variable
wrd 	EQU 0x49 	; word size temporary variable

; start up
	ORG 0x0000
	BCF PCLATH,3
	BCF PCLATH,4
	GOTO start
; Interrupt always at address 0004
	ORG 0x0004
	MOVWF W_TEMP    ; save registers
	SWAPF STATUS,W
	CLRF STATUS
	MOVWF STATUS_TEMP
	CALL ISR	; call interrupt service routine
	SWAPF STATUS_TEMP,W
	MOVWF STATUS
	SWAPF W_TEMP,F
	SWAPF W_TEMP,W  ; restore registers
	RETFIE

start:
; setup PIC
	BSF STATUS,RP0 	; select page 1
	MOVLW 0x72
	MOVWF 0x0F 	; set internal RC select to 8MHz
	MOVLW 0xC0
	MOVWF 0x06 	; set PORTB 0-5 pins as outputs, 6 & 7 inputs

; initialise adc
	MOVLW 0xFF
	MOVWF 0x05 	; set portA as input
	MOVLW 0x0F
	MOVWF 0x1B 	; set PORTA pins 0-3 as analog inputs
	MOVLW 0x80
	MOVWF 0x1F 	; set 10 bit A/D result format right justify ADRESH/L
	BCF STATUS,RP0 	; select page 0
	MOVLW 0xC1
	MOVWF 0x1F 	; set A/D conversion clock to internal source, turn on adc
	BSF STATUS,RP0 	; select page 1
	MOVLW 0x7F
	MOVWF 0x01 	; enable PORTB weak pullups for inputs 6 & 7

; setup UART
	BSF STATUS,RP0 	; select page 1
	BSF 0x0C,5 	; enable UART RX interrupt
	MOVLW 0x08
	MOVWF SPBRG 	; set UART BAUD rate 57600
	BSF TRISB,2
	BSF TRISB,5 	; set PORTB bits 2 and 5 as outputs for UART
	MOVLW 0x24
	MOVWF TXSTA 	; enable Transmitter set High BAUD rate select bit
	BCF STATUS,RP0
	MOVLW 0x90
	MOVWF RCSTA 	; enable Serial port, continuous enable receiver
	MOVLW 0xC8
	MOVWF 0x0B 	; enable GIE, PEIE and RBIE for UART

; initialise variables
	BCF STATUS,RP0 	; select page 0
	CLRF 0x06 	; clear PORTB
	MOVLW 0xC0
	ANDWF 0x06,W
	MOVWF oldb 	; last value of PORTB bits 6 & 7 for change of state
; Send "OK"		; start up ok
	MOVLW "O"
	CALL TXD
	MOVLW "K"
	CALL TXD