;----------------------------------------------------------------------; ; BINCNT4M.ASM Counts in binary on LEDs (RB0 - RB4) 4 MHz oscillator ; ;----------------------------------------------------------------------; ; PIC16F84 ; .-----------. ; -|RA2 RA1|- V+ 4.5 or 5 Volts ; -|RA3 RA0|- ; -|RA4 OSC1|--|X|___ gnd ; V+ ---|MCLR OSC2|--|X| ; gnd ---|Vss Vdd|--- V+ ; gnd ---|<--{r}--|RB0 RB7|- ; gnd ---|<--{r}--|RB1 RB6|- -{r}- 470 ohm ; gnd ---|<--{r}--|RB2 RB5|- -|<- LED ; gnd ---|<--{r}--|RB3 RB4|- -|X|_ 4 MHz cer. res. ; '-----------' -|X| w/caps 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 CBLOCK H'0C' ; set up general registers starting at ; address 12 counter ; a general counting register ENDC ; end of register definitions ORG 0 ; start at program memory location zero ;----------------------------------------------------------------------; ; First we set up all bits of PORT A and B as outputs ; ; and set bits in the OPTION register concerning TMR0 ; ;----------------------------------------------------------------------; movlw B'00000000' ; all bits low in W tris PORTA ; make all bit of PORT A outputs ... tris PORTB ; and all bits of PORT B also movlw B'00000101' ; TMR0 assigned to incr. on internal clk ; prescalar assigned to TMR0 and set 1:64 ; bit 5 set means timer runs off RA4 option ; W inserted into OPTION register ; check OPTION register in data sheet ;----------------------------------------------------------------------; ; This is the main program ; ;----------------------------------------------------------------------; clrf PORTB ; start with zero in port B ; all LEDs off again: movlw D'61' ; set up a counter to count down from 61 movwf counter incf PORTB, f ; add 1 to port B, (next binary byte) ; The instructions from loop to goto loop are executed about 61 times ; a second. The majority of this time is taken up in the 2 instruction ; loop made up by the next two instructions. This simply waits for the ; timer zero interrupt flag to be set which happens after timer zero ; overflows. TMR0 overflows after going from 255 to 0. TMR0 normally ; runs at a rate of crystal freq/4 but we have added a 1:64 prescalar ; which make the increment every 64 microseconds or a overflow after ; 256 * 64 = 16384 usec. 61 of these gives 999424 usec. loop: btfss INTCON, T0IF ; wait on T0IF set, skip next when set goto $ -1 ; T0IF not set yet continue to loop bcf INTCON, T0IF ; clear interrupt flag, timer runs always decfsz counter, f ; decrement counter, skip if zero goto loop ; if counter not zero, wait on T0IF again ; once 61 cycles of waiting for T0IF have happened we go back and ; reset the counter to 61 and bump the binary number displayed by one goto again end ; end of program
file: /Techref/piclist/cheapic/bincnt4m.asm, 3KB, , updated: 2000/12/8 12:43, local time: 2024/8/14 23:29,
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