;----------------------------------------------------------------------; ; EGGTIM4M.ASM A 3 minute countdown timer for boiling eggs, 4 MHz osc; ; Pushbutton on RB4 starts countdown. Displays minutes and tens of ; ; seconds in binary on LEDs. Zero represented by all leds lit. ; ; A second pushbutton can be added to cycle through starting times. ; ;----------------------------------------------------------------------; ; .-----------. ; -|RA2 RA1|- V+ = 4.5 or 5 Volts ; -|RA3 RA0|- X = 4 MHz cer. res. ; -|RA4 OSC1|--|X|___ gnd ; -{r}- = 470 ohm V+ ---|MCLR OSC2|--|X| ; -|<- = LED gnd ---|Vss Vdd|--- V+ ; gnd ---|<--{r}--|RB0 RB7|- ; gnd ---|<--{r}--|RB1 RB6|- ; gnd ---|<--{r}--|RB2 RB5|---[PB]--- gnd ; gnd ---|<--{r}--|RB3 RB4|---[PB]--- gnd ; '-----------' ; PIC16F84 -[PB]- pushbutton LIST P=16F84 ; tells which processor is used INCLUDE "p16f84.inc" ; defines various registers etc. Look ERRORLEVEL -224 ; supress annoying message from tris __CONFIG _PWRTE_ON & _XT_OSC & _WDT_OFF ; config. switches #DEFINE button1 PORTB, 4 ; RB4 pushbutton to ground #DEFINE button2 PORTB, 5 ; RB5 pushbutton to ground ;----------------------------------------------------------------------; ; Here we set up the user defined registers ; ;----------------------------------------------------------------------; CBLOCK H'0C' ; first free register address is 12 sec ; keeps track of seconds sec10 ; keeps track of tens of seconds mins ; keeps track of minutes cntmsec ; counter used in millisecond delays counter ; general counter ENDC ORG 0 ; start a program memory location zero goto main ; jump over the interrupt routine ;----------------------------------------------------------------------; ; initialize the ports, set up interrupts etc: ; ;----------------------------------------------------------------------; init: movlw B'00000000' ; all outputs tris PORTA ; on PORT A movlw B'00110000' ; RB4 & RB5 inputs, all others outputs tris PORTB ; on PORT B movlw B'00000000' ; port B pull-ups active option clrf sec ; sec = 0 clrf sec10 ; sec10 = 0 movlw D'3' ; and minutes = 3 movwf mins movlw D'10' ; initialize counter to 10 movwf counter return ;----------------------------------------------------------------------; ; Wait for pushbutton. Start countdown when pressed. ; ;----------------------------------------------------------------------; waitpushbutton: movf mins, W ; display minutes on LEDs at start movwf PORTB ; to add a pushbutton on RB5 to select starting minutes uncomment the ; next two instructions ; btfss button2 ; button2 pressed? skip if not ; call selectstart ; select starting number of mins 1-16 btfsc button1 ; switch closed, (gives 0)? goto waitpushbutton ; not yet ; switch has been detected closed ; ( no debounce necessary ) clrf PORTB ; lights out return ;----------------------------------------------------------------------; ; Select the starting number of minutes 1-15 ; ;----------------------------------------------------------------------; selectstart: incf mins, W ; increment minutes andlw H'0F' ; limit to 15 movwf mins ; store in mins waitup: movlw 10 ; delay for 10 msec (debounce press) call nmsec btfss button2 ; button 2 up yet? goto waitup ; no, keep checking return ;----------------------------------------------------------------------; ; This is the main program ; ;----------------------------------------------------------------------; main: call init ; set up ports, initialize registers call waitpushbutton ; wait for button to be pressed loop: decfsz counter, f ; show time every tenth time goto $ +2 ; skip over next instruction goto showtime ; display time, (lasts 1 sec) call onesecond ; delay for one second nextsec: decf sec, f ; down one sec movlw H'FF' ; check for underflow subwf sec, W ; will give zero if underflow btfss STATUS, Z ; skip if underflow goto loop ; else continue movlw D'9' ; sec to 9 movwf sec decf sec10, f ; same for sec10 register movlw H'FF' ; check for underflow subwf sec10, W ; gives zero if underflow btfss STATUS, Z ; skip if underflow goto loop ; else continue movlw D'5' ; sec10 to 5 movwf sec10 decf mins, f ; now minutes movlw H'FF' ; check for underflow subwf mins, W ; gives zero if underflow btfss STATUS, Z ; skip if underflow goto loop ; else continue ; come here when the countdown is over finished: movlw H'0F' ; turn on all leds indicating finish movwf PORTB movlw D'40' ; wait for 10 seconds movwf counter call msec250 ; 1/4 sec delay decfsz counter, f ; finished? goto $ -2 ; not yet goto main ; start all over again showtime: ; this lasts approximately one second ; usec instructions are insignificant compared to 100's of msec movf mins, W ; display minutes btfsc STATUS, Z ; skip if not zero movlw H'0F' ; else all LEDs on movwf PORTB ; turn on LEDs call msec250 ; on for 400 msec movlw D'150' call nmsec clrf PORTB ; blank briefly movlw D'200' call nmsec movf sec10, W ; now the same with sec10 btfsc STATUS, Z ; skip if not zero movlw H'0F' ; else all LEDs on movwf PORTB ; show 10's of seconds call msec250 ; on for 400 msec movlw D'150' call nmsec clrf PORTB ; blank movlw D'10' ; reset counter to 10 movwf counter goto nextsec ;----------------------------------------------------------------------; ; time delay routines ; ;----------------------------------------------------------------------; micro4 addlw H'FF' ; subtract 1 from 'W' btfss STATUS,Z ; skip when you reach zero goto micro4 ; more loops return ;*** N millisecond delay routine *** msec250: movlw D'250' ; 250 millisecond delay nmsec: movwf cntmsec ; delay for N (in W) millisec msecloop: movlw D'248' ; 1 usec for load call micro4 ; this instruction is 995 usec nop ; 1 usec decfsz cntmsec,f ; 1 usec, (2 if skip taken) goto msecloop ; 2 usec, loop = 995+5 = 1 msec return onesecond: call msec250 ; delay for one second call msec250 call msec250 call msec250 return end ; end of program ; Note: This program differs from eggtimer.asm (used a 32 kHz xtal). ; That program has errors due to subtile interaction of the isr and main ; program. The easiest fix is to not use a interrupt subroutine. <P> </BODY></HTML>
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