Program E :

;************************************
; written by :	John Morton			*
; date : 26/07/97				*
; version : 1.0					*
; file saved as : Traffic			*
; for PIC54					*
; clock frequency : 3.82 MHz		*
;************************************

; PROGRAM FUNCTION : A pedestrian traffic lights junction is simulated.

 		list 	     	P=16C54
		include		"c:\pic\p16c5x.inc"

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

		porta		equ	05
		portb		equ	06
		
		Mark15	equ	08
		Post80		equ	09
		Counter16	equ	0A
		Counter8	equ	0B

		org		1FF
		goto		Start
		org		0

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

Init		clrf		porta		; resets inputs and outputs
		clrf		portb		;
		movlw		b'0001'	; RA0 : push button, RA1-3 : not connected
		tris		porta		;   		
		movlw		b'00000000' 	; Motorists : RB0 : green, RB1 : amber,
		tris		portb		;  RB2 : red.  Pedestrians : RB4 : green, 
						;  RB5 : red, RB3 and RB6-7 : not connected
		movlw		b'00000111'	; sets up timing register
		option

		retlw		0

delay		movlw		d'15'		; moves the decimal number 15 into
		movwf		Mark15	;   the G.P.F. called Mark15

		movlw		d'80'		; moves the decimal number 80 into
		movwf		Post80		;   the G.P.F called Post80

TimeLoop	movfw		Mark15	; takes the number out of Mark15
		subwf		TMR0, w	; subtracts this number from the number in
						;   TMR0, leaving the result in the working 						;   register (and leaving TMR0 unchanged)
		btfss		STATUS, Z	; tests the Zero Flag - skip if set, i.e. if the result 						;   is zero it will skip the next instruction
		goto		TimeLoop	; if the result isn't zero, it loops back to 'Loop'
		
		movlw		d'15'		; moves the decimal number 15 into the working
		addwf		Mark15, f	;   register and then adds it to 'Mark15'

		decfsz		Post80, f	; decrements 'Post80', and skips the next 						;   instruction if the result is zero
		goto		TimeLoop	; if the result isn't zero, it loops back to 'Loop'
		retlw		0		; when half a second has passed, it returns

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

Start		call		Init		

Main		movlw		b'00010100'	; motorists : green on, others off
		movwf		portb		; pedestrians : red on, others off

ButtonLoop	btfss		porta, 0	; is the pedestrian's button pressed?
		goto		ButtonLoop	; no, so loops back

		bsf		porta, 1	; turns motorist's amber light on
		bcf		porta, 2	; turns motorist's green light off

		call		delay		; waits half a second
		call		delay		; waits half a second
		call		delay		; waits half a second
		call		delay		; waits half a second

		movlw		b'00100001'	; motorists : red on, amber off
		movwf		portb		; pedestrians : green on, red off

		movlw		d'16'		; moves the decimal number 16 into the general
		movwf		Counter16	;   purpose file register called Counter16
Loop8		call		delay		; creates half second
		decfsz		Counter16, f	; does this sixteen times
		goto		Loop8		; loops back until eight seconds have passed

		bsf		porta, 1	; turns motorist's amber light on
		bcf		porta, 2	; turns motorist's red light off 

		movlw		d'8'		; moves the decimal number 8 into Counter8
		movwf		Counter8	;
FlashLoop	movlw		b'00100000'	; toggles the green pedestrian light
		xorwf		portb, f	;
		call		delay		; creates half second delay
		decfsz		Counter8, f	; makes it happen eight times
		goto		FlashLoop	; loops back
		goto		Main		; loops back to start
			
END