利用单个PIC输入监控15个触点

作为一个简单实用的示例，图1中的电路利用一个8位PIC微控制器控制一个4位LED显示器，显示出按下了哪个按钮。当任意按钮被按下时，比较器中断程序会立即作出响应。该程序会在VREF值之间进行循环，直至比较器输出COUT返回高电平，表明该按钮被按下。完整注释的汇编程序源代码总共不到100字。该代码并未作过度优化，从而可方便理解或易于转化到其他控制器上。

汇编程序源代码:

; MULTIBTN.ASM: sensing upto 15 pushbuttons with one I/O (pin6: GP1/CIN-)

; BENABADJI Noureddine - ORAN - Dec. 11...14th, 2013

;

Errorlevel -302 ; avoid warning #302: Register in operand not in bank0.

; Ensure that bank bits are correct.

List P = 12F683

#include "p12f683.inc"

__CONFIG _INTOSCIO&_MCLRE_OFF&_PWRTE_ON&_WDT_OFF&_FCMEN_OFF&_IESO_OFF&_BOD_ON&_CPD_OFF&_CP_OFF

#define LED1 GPIO, 0 ; output bit0 of the 4-bit binary LED display

#define LED2 GPIO, 2 ; output bit1 of the 4-bit binary LED display

#define LED3 GPIO, 4 ; output bit2 of the 4-bit binary LED display

#define LED4 GPIO, 5 ; output bit3 of the 4-bit binary LED display

;----------------------------- define variables ------------------------------

CBLOCK 0x20 ; bank0 = [0x20...0x7F] = 94 bytes

;delay

cnt1, cnt2, cnt3 ; counters

ENDC

;------------------------------------------------------------------------------

BANK0 macro

BCF STATUS, RP0 ; bank0

endm

;------------------------------------------------------------------------------

BANK1 macro

BSF STATUS, RP0 ; bank1

endm

;------------------------------------------------------------------------------

SIregGEval8b macro file, val, jmpOk ; if (file >= val) goto jmpOk ;

MOVLW val

SUBWF file, w ; w = file - val

BTFSC STATUS, C

GOTO jmpOk ; yes

endm

;/////////////////////////////////////////////////////////////////////////////

; MAIN PROGRAM

;/////////////////////////////////////////////////////////////////////////////

ORG 0x00 ; reset vector

GOTO Setup

ORG 0X04 ; interrupt vector

GOTO IntCmp

;/////////////////////////////////////////////////////////////////////////////

;-----------------------------------------------------------------------------

LEDsOFF

CALL Delay256ms

CLRF GPIO ; all LEDs off

RETLW 0

;-----------------------------------------------------------------------------

Delay256ms

CLRF cnt2

CLRF cnt1

NOP ; 1us

DECFSZ cnt1, f ; 1us

GOTO $-2 ; 2us => 4*256 = 1024 us, approx. 1 ms internal delay loop

DECFSZ cnt2, f ; approx. 256 ms external delay loop

GOTO $-4

RETLW 0[page]

;/////////////////////////////////////////////////////////////////////////////

Setup

BANK1

CLRF TRISIO ; config. all I/O as outputs

BCF OPTION_REG, T0CS ; use pin5 as GP2, not TOCKI

CLRF ANSEL ; use all AN as digital I/O

BANK0

CLRF GPIO ; all LEDs off

MOVLW b'00000111'

MOVWF CMCON0 ;comparator off

splash ; (initial test for LEDs)

BSF LED1

CALL LEDsOFF

BSF LED2

CALL LEDsOFF

BSF LED3

CALL LEDsOFF

BSF LED4

CALL LEDsOFF

;;;;;;;;;;

initializeComparator

BANK1

MOVLW b'00001010' ;config. GP1 as input (will be CIN-)

MOVWF TRISIO

;BANK0

MOVLW b'10100001'

;BANK1

MOVWF VRCON ;Vref on, low range, VR=0001 => ratio = 1/24

BANK0

MOVLW b'00000100'

MOVWF CMCON0 ;comparator on: CIN- = GP1; CIN+ = Vref; Cout internal

;;;;;;;;;

;enable interrupt

BANK1

BSF INTCON, PEIE ; enable interrupt on Comparator trip

BSF PIE1, CMIE ; enable interrupt on Comparator trip

BANK0

BSF INTCON, GIE ; set general interrupt enable

goto $ ; infinite loop (waiting for an interrupt)

;-----------------------------------------------------------------------------

; Comparator trip interrupt routine

;-----------------------------------------------------------------------------

IntCmp

;don't need to save any context, only interrupting a goto $

BANK0

MOVLW .1

MOVWF cnt3

nextBtn

INCF cnt3, F

SIregGEval8b cnt3, .16, whichBtn ; if (cnt3 >= 16) goto whichBtn ;

MOVLW b'10100000'

ADDWF cnt3, W

BANK1

MOVWF VRCON ;Vref on, low range, VR=cnt3

BANK0

BTFSS CMCON0, COUT ; Cout == 1 ?

GOTO nextBtn

whichBtn

DECF cnt3, F
 

BTFSC cnt3, 0

BSF LED1

BTFSC cnt3, 1

BSF LED2

BTFSC cnt3, 2

BSF LED3

BTFSC cnt3, 3

BSF LED4

CALL LEDsOFF

endIntCmp

MOVLW b'10100001'

BANK1

MOVWF VRCON ;Vref on, low range, VR=0001 => ratio = 1/24

BANK0

BCF PIR1, CMIF ; clear comparator interrupt flag

RETFIE

;-----------------------------------------------------------------------------

END