PROGRAM O

;************************************ ***
; written by: John Morton		* 
; date: 10/01/05			*	 
; version 1.0 			*	 
; file saved as phonecard.asm	* 
; for P12F675			* 
; clock frequency: internal 4MHz	*	 
; ***************************************  

; Program Description: A smart card for a phone box  		
	
		list		P=12F675		 	
		include		"c:\pic\p12f675.inc"
	
;============== 
; Declarations:  

W_temp		equ		20h 
STATUS_temp     equ		21h  
temp		equ		22h		
Mark125		equ		23h
Post125		equ		24h
Post15		equ		25h
	
		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'111110'	; all inputs except GP0
		movwf		TRISIO	;   
		clrf		WPU	;  weak pull-ups disabled 
		movlw		b'11000111'	; sets up timer and some pin	
		movwf		OPTION_REG	;  settings 		
		clrf		PIE1	; turns off peripheral ints. 
		clrf		IOC	; disables GPIO change int. 
		clrf		VRCON	; turns off comparator V. ref. 	
		clrf		ANSEL	; makes GP0:3 digital I/O pins
		
		bcf		STATUS, RP0	; back to Bank 0 
		clrf		GPIO	; resets input/output port
		movlw		b'00010000'	; sets up interrupts
		movwf		INTCON	;
		movlw		b'00000111'	; turns off comparator
		movwf		CMCON	; 		
		clrf		T1CON	; turns off TMR1 		
		clrf		ADCON0	; turns off A to D conv.  		
		
		movlw		d'125'	; sets up postscalers
		movwf		Post125	;
		movlw		d'15'	; 
		movwf		Post15	;
		retfie 			;  returns from Init

isr		movwf		W_temp	; stores w.reg in temp register 	
		movfw		STATUS	; stores STATUS in temp	
		movwf		STATUS_temp	;  register  		
	
		bcf		INTCON, 1	; resets INT interrupt flag
		bcf		STATUS, RP0	; makes sure weÕre in Bank 0
 		movfw		GPIO	; reads value of GPIO 
		movwf		temp	; 
 		rrf		temp, f	; rotates right three timesÉ 
		rrf		temp, f	;	
 		rrf		temp, w	; Éleaving result in w. reg 
		andlw		b'000111'	; masks bits 3-5 
		call		CardValue	; converts code into minutes 

		bsf		STATUS, RP0	; goes to Bank 1
		movwf		EEDATA	; stores minutes in EEDATA
 		clrf		EEADR	; selects EEPROM address 00h 
		bsf		EECON1, 2	; enables a write operation  
		movlw		0x55	; now follows the Ôsafe  
		movwf		EECON2	;  combinationÕ
 		movlw		0xAA 	;
		movwf		EECON2	; 
		bsf		EECON1, 1	; starts the write operation
EELoop		btfsc		EECON1, 1	; has write operation finished?
		goto		EELoop	; no, still high, so keeps looping

 		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
 
CardValue	addwf		PCL, f	; returns with new number of 
		retlw		d'2'	; minutes for the card
	 	retlw		d'5'	;
		retlw		d'10'	; 
		retlw		d'20'	; 
		retlw		d'40'	;
	 	retlw		d'60'	; one hour
	 	retlw		d'120'	; two hours 
		retlw		0	; (erases card) 

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

Start		call		Init	; initialisation routine 

Main		bsf		STATUS, RP0	; selects Bank 1 
		clrf		EEADR	; selects EEPROM address 00h
 		bsf		EECON1, 0	; initiates an EEPROM read
 		movfw		EEDATA	; reads EEDATA
 		bcf		STATUS, RP0	; selects Bank 0
 		btfss		STATUS, Z	; is it 0? 
		goto		Active	; no, so goes to Active 
 		bcf		GPIO, 0	; turns off GP0
 		sleep			; goes to sleep
 		nop			; 		 	
		goto		Main	; loops back to Main

Active		bsf		GPIO, 0	; turns on GP0
		btfss		GPIO, 1	; is a call in progress? 
		goto		Active	; no, so keeps waiting
  		movfw		Mark125	; has one minute passed? 
		subwf		TMR0, w	; 	
		btfss		STATUS, Z	; 
 		goto		Active	; no, so keeps looping 		
 	
		movlw		d'125'	; 
		addwf		Mark125	; 	
		decfsz		Post125	;
 		goto		Active	; 		
 		
		movlw		d'125'	; 
		movwf		Post125	;
		decfsz		Post15	; 
		goto		Active	; 
 		
		movlw		d'15'	; one minute has passed, so				movwf		Post15	;  resets final postscaler 
 		bsf		STATUS, RP0	; goes to Bank 1
		clrf		EEADR	; selects EEPROM address 00h 
	 	bsf		EECON1, 0	; reads EEPROM address 00h 	
		decf		EEDATA	; subtracts 1 minute from card
	 	bsf		EECON1, 2	; enables a write operation 
		bcf		INTCON, 7	; disables global interrupts  
		movlw		0x55		; now follows the Ôsafe 
 		movwf		EECON2	;  combinationÕ 
		movlw		0xAA	; 
		movwf		EECON2	; 
		bsf		EECON1, 1	; starts the write operation 
EELoop		btfsc		EECON1, 1	; has write operation finished?
		goto		EELoop	; no, still high, so keeps looping

		bcf		STATUS, RP0	; back to Bank 0 
		bsf		INTCON, 7	; enables global interrupts 
		goto		Main	; loops back to start  	

		END