PROGRAM P

;***************************************
; written by: John Morton		*
; date: 14/03/05			*	
; version: 1.0			*		
; file saved as: tempsense.asm	*
; for PIC12F675			*
; clock frequency: Int. 4 MHz	*	
; ***************************************

; Program Description: Bath temperature measuring device

		list		P=12F675		
		include		"c:\pic\p12f675.inc"

;==============
; Declarations:

W_temp		equ		20h
STATUS_temp    equ		21h

		org		0	; first instruction to be executed
		goto		Start	;
		
		org		4	; interrupt service routine
		goto		isr	;

;===========
; Subroutines: 

Init		bsf		STATUS, RP0	; goes to Bank 1
		call		3FFh	; calls calibration address
		movwf		OSCCAL	; moves w. reg into OSCCAL
		movlw		b'010000'	; GP0-2 are LEDs, GP4 analogue
		movwf		TRISIO	;  input
		clrf		WPU	; weak pull-ups disabled

		movlw		b'10000000'	; weak pull-ups disabled, no timer 			movwf		OPTION_REG	;  used
		movlw		b'01000000'	; enables A/D interrupt
		movwf		PIE1	; 	
		clrf		IOC	; disables GPIO change int.
		clrf		VRCON	; turns off comparator V. ref.
		movlw		b'00011000'	; A/D clock: Fosc/8 = 2µs; AN3/GP4
		movwf		ANSEL	; is anal. input, others are digital
	
		bcf		STATUS, RP0	; back to Bank 0
		clrf		GPIO	; resets input/output port
		movlw		b'01000000'	; enables peripheral interrupts
		movwf		INTCON	;
		movlw		b'00000111'	; turns off comparator
		movwf		CMCON	;
		clrf		T1CON	; turns off TMR1
		movlw		b'00001101'	; Turns on ADC, selects AN3, 
		movwf		ADCON0	;  relative to VDD, left-justified

		retfie 			;

isr		movwf		W_temp	; stores w.reg in temp register
		movfw		STATUS	; stores STATUS in temporary 
		movwf		STATUS_temp	;  register
	
		bcf		STATUS, RP0	; goes to Bank 0
		bcf		PIR1, 6	; clears A/D interrupt flag

		bsf		STATUS, RP0	; goes to Bank 1
		movlw		0x80	; subtracts lower byte
		subwf		ADRESL, w	; 
		comf		STATUS, w	; inverts carry flag (bit 0 of STATUS)
		andlw		b'00000001'	; masks all other bits
		bcf		STATUS, RP0	; goes to Bank 0
		addlw		0x12	; add this to the number we are
		subwf		ADRESH, w	;  subtracting from the higher byt4
		btfss		STATUS, C	;
		goto		Cold	; ADRESH:L < 0x1280, so Òcold!Ó

		bsf		STATUS, RP0	; goes to Bank 1
		movlw		0x80	; subtracts lower byte
		subwf		ADRESL, w	; 
		comf		STATUS, w	; inverts carry flag (bit 0 of STATUS)
		andlw		b'00000001'	; masks all other bits
		bcf		STATUS, RP0	; goes to Bank 0
		addlw		0x15	; add this to the number we are
		subwf		ADRESH, w	;  subtracting from the higher byt
		btfss		STATUS, C	;
		goto		OK	; ADRESH:L < 0x1580, so OK
		goto		Hot	; ADRESH:L = 0x1580, so Hot!

Cold		movlw		b'000001'	; turns on ÔcoldÕ LED
		movwf		GPIO	;
		goto		prereturn	; 

OK		movlw		b'000010'	; turn on ÔOKÕ LED
		movwf		GPIO	;
		goto		prereturn	;

Hot		movlw		b'000100'	; turn on ÔHotÕ LED
		movwf		GPIO	;
		goto		prereturn	;

prereturn	movfw		STATUS_temp	; restores STATUS register to
		movwf		STATUS	;  original value
		swapf		W_temp, f	; restores working register to
		swapf		W_temp, w	;  original value
		retfie			; returns, enabling GIE

;============
; Program Start

Start		call		Init	; sets everything up
Main		bsf		ADCON0, 1	; start A/D conversion
		goto		Main	;		

		END