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660	Appendix D

	processor 16f84A
	include		<p16f84A.inc>
	__config		_XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF
;=====================================================
;			PIC register equates
;=====================================================
porta	equ		0x05
portb	equ	0x06
status	equ		0x03
z			equ	0x02
c			equ	0x00
tmr0	equ		0x01
; countL	equ		0x01	; Alias for tmr0
;
;=====================================================
;		variables in PIC RAM
;=====================================================
; Local variables
	cblock		0x0d	; Start of block
	J			; counter J
	K			; counter K

;3-byte auxiliary counter. Low order byte is kept

;in the timer0 register

countM	; Medium byte
countH	; High byte

endc

;========================================================

; m a i n p r o g r a m

;========================================================

	org	0	; start at address 0
	goto	main
;
;=============================
;	interrupt handler
;=============================
	org		0x04

;goto IntServ ;=============================

;main program ;============================= main:

;Clear the watchdog timer and reset prescaler clrf tmr0

clrwdt

;Set up the OPTION register bit map

Supplementary Programs										661
			movlw			b'11011000'
;	7	6	5	4	3	2 1 0 <= OPTION bits
;	\|	\|	\|	\|	\|	\|__\|__\|_____	PS2-PS0 (prescaler bits)
;	\|	\|	\|	\|	\|		Values for Timer0
;	\|	\|	\|	\|	\|		*000		= 1:2	001 = 1:4
;	\|	\|	\|	\|	\|		010		= 1:8	011 = 1:16
;	\|	\|	\|	\|	\|		100		= 1:32	101 = 1:64
;	\|	\|	\|	\|	\|		110		= 1:128 *111 = 1:256
;	\|	\|	\|	\|	\|______________		PSA		(prescaler assign)
;	\|	\|	\|	\|			1	=	to WDT
;	\|	\|	\|	\|			*0	=	to Timer0
;	\|	\|	\|	\|_________________			TOSE (Timer0 edge select)
;	\|	\|	\|				0	=	increment on low-to-high
;	\|	\|	\|				*1	=	increment in high-to-low
;	\|	\|	\|____________________				TOCS (TMR0 clock source)
;	\|	\|					*0	=	internal clock
;	\|	\|					1	=	RA4/TOCKI bit source
;	\|	\|_______________________					INTEDG (Edge select)
;	\|						*0	=	falling edge

;|__________________________ RBPU (Pullup enable)

;		0 = enabled
;		*1 = disabled
option
; Setup ports
movlw	0x00	; Set port B to output
tris	portb
clrf	portb	; All port B to 0
; Port A is not used in this program
mloop:
bsf	portb,0
call	TM0delay
bcf	portb,0
call	TM0delay
goto	mloop

;*********************************

;one second delay sub-routine

;using Timer0 ;*********************************

;Routine logic:

;The prescaler is assigned to timer0 and setup so

;that the timer runs at 1:2 rate. This means that

;every time the counter reaches 128 (0x80) a total

;of 256 machine cycles have elapsed. The value 0x80

;is detected by testing bit 7 of the counter

;register. This method gives the routine a total of

;128 machine cycles before the next counter beat must

;be acknowledged.

TM0delay:

662	Appendix D

;Timer is designed to count from 0 to 1,000,000

;1,000,000 = 0x0f 0x42 0x40

;	---- ---- ----
;	\|	\|	\|___	(see note)
;	\|	\|________		countM
;	\|_____________			countH

;Note:

;The initial count of 0x40 (64 decimal) is ensured

;by initializing the tmr0 register to count 32 timer

;beats at the 1:2 prescaler rate. 128 - 32 = 96 = 0x60

;Initialize the counters:

movlw 0x0f

movwf countH

movlw 0x42

movwf countM

movlw 0x60

movwf tmr0

;Routine tests timer overflow by testing bit 7 of

;the tmr0 register.

cycle:

movlw 3

subwf tmr0,w

btfsc status,c

goto cycle

;Subtract 256 from beat counter by decrementing the

;mid-order byte

decfsz countM,f

goto

cycle

; Continue if mid-byte not

zero

;At this point the mid-order byte has overflowed.

;High-order byte must be decremented.

decfsz countH,f

goto cycle

; At this point one second has elapsed

return

end

Supplementary Programs

663

; File name: SevenSeg.asm

;Date: April 19, 2006

;Author: Julio Sanchez

;Reference: SevenSeg Circuit and Board

;Description:

;Test program for reading four toggle switches and

;displaying the represented hex number on seven-segment

;LED. Also contains a pushbutton switch to activate a

;piezo buzzer. Switches are wired active low.

;

; Switches used in __config directive:

;		_CP_ON	Code protection ON/OFF
; *		_CP_OFF
;	*	_PWRTE_ON	Power-up timer ON/OFF

;_PWRTE_OFF

;	_WDT_ON	Watchdog timer ON/OFF
; * _WDT_OFF
;	_LP_OSC	Low power crystal occilator
; * _XT_OSC		External parallel resonator/crystal oscillator
;	_HS_OSC	High speed crystal resonator (8 to 10 MHz)
;		Resonator: Murate Erie CSA8.00MG = 8 MHz
;	_RC_OSC	Resistor/capacitor oscillator (simplest, 20%

error)

;|_____ * indicates setup values

;=========================

;setup and configuration ;=========================

processor 16f84A include <p16f84A.inc>

__config _XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF

;

;=====================================================

;	constant definitions
;	(per circuit wiring diagram)

;=====================================================

#define Pb_sw 4 ; Port A line 4 to push button switch

;

;=====================================================

; PIC register equates

;=====================================================

Porta	equ	0x05
Portb	equ	0x06

;============================

664			Appendix D
;	local variables
;============================
	cblock	0x0c	; Start of block
	J		; counter J
	K		; counter K
	endc
;============================================================
;			program
;============================================================
	org	0	; start at address 0
	goto	main
;
; Space for interrupt handlers
	org	0x08

main:
; Port A. Five low-order lines set for input
movlw	B'00011111'	; w = 00011111 binary
tris	porta	; port	A (lines	0 to 4) to
input
; Port B. All eight lines for output
movlw	B'00000000'	; w :=	00000000	binary
tris	portb	; port	B to output

;===============================

;Pushbutton switch processing ;=============================== pbutton:

;Push button switch on demo board is wired to port A bit 4

;Switch logic is active low

btfss	porta,Pb_sw	; Test and skip if switch bit
		; set
goto	buzzit	; Buzz if switch ON,
; At this point port A bit 4 is set (switch is off)
call	buzoff	; Buzzer off
goto	readdip	; Read DIP switches
buzzit:
call	buzon	; Turn on buzzer
goto	pbutton

;============================

;dip switch monitoring ;============================ readdip:

;Read port A switches

movf

porta,w

; Port A bits to w

;Since board is wired active low then all switch bits

;must be negated. This is done by XORing with 1-bits

xorlw

b'11111111'

; Invert all bits in w

; Mask off 4 high-order bits

Supplementary Programs		665
andlw	b'00001111'	; And with mask

;At this point the w register contains a 4-bit value

;in the range 0 to 0xf. Use this value (in w) to

;obtain seven-segment display code

call	segment
movwf	portb		; Display switch bits
goto	pbutton
;================================
; routine to returns 7-segment
;	codes
;================================
segment:
	addwf	PCL,f	; PCL is program counter latch
	retlw	0x3f	; 0 code
	retlw	0x06	; 1
	retlw	0x5b	; 2
	retlw	0x4f	; 3
	retlw	0x66	; 4
	retlw	0x6d	; 5
	retlw	0x7d	; 6
	retlw	0x07	; 7
	retlw	0x7f	; 8
	retlw	0x6f	; 9
	retlw	0x77	; A
	retlw	0x7c	; B
	retlw	0x39	; C
	retlw	0x5b	; D
	retlw	0x79	; E
	retlw	0x71	; F
	retlw	0x7f	; Just in case all on