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'tmr0+counter?? wont work!'
1999\04\15@215102 by Glen

thanks for taking the time & your help!

i'm new to this !
i cant get the tmr0 + counter to work in the 16f84.
i don't know why ?

i am trying to get the tmr0 to turn over every 10 ms
at each tmr0 turnover the counter decrements & when counter = 0 will
stop the program

can anyone help me as to where the problem is ?
columns have been checked & ok !
below is where i'm at:

;  **********************   *
; Notes:   This program is to operate as follows ,                    *
; after the zero crossing , start timer  times out then         *
; 2 outputs ( portb bits 4,5 ) toggle
; after each timeout the counter decrements until 0
;then the outputs stay off       *
list      p=16F84             ; list directive to define processor
#include <>         ; processor specific variable definitions


;   vars
porta        equ     0x05      ;CPU equates (program memory map)
portb        equ     0x06      ;CPU equates (program memory map)
souter       equ     0x0c     ;
sinner        equ     0x0d     ;
inners        equ     0x0e     ;
outers       equ     0x0f     ;
innerf        equ      0x10     ;
outerf        equ     0x11     ;
timfin         equ     0x12     ;
starttmr     equ     0x13     ; free reg ??
status         equ     0x03    ;CPU equates (program memory map)
w               equ     0          ; destination designators
f               equ         1         ; destination designators
z                 equ     0         ; destination designators

;                   porta set-up
           org         0x000             ;address 000 program start
start      movlw    0xff              ;ff hex moved to w register
           tris           porta             ;porta set as inputs
;                    portb set-up
       movlw   0x0c              ;00001100 hex moved to w register
       tris        portb             ;portb set outputs 0,1,4,5,6,7,
inputs 2,3
;       ============== program start =============
       movlw     0x00              ;move 00 hex to register w
        movwf     portb             ;move register w to portb (clear

; set up timer and prescaler regs
        movlw     b'10010111' ; prescaler setup for 1:256

           movlw      125
            movwf      starttmr          ; 125 * 10ms -> 250ms

initmr     movlw      -156
            movwf      TMR0           ; 156 * prescaler(256) * (4MHz)
=> 10ms approx

loop   call chcycs          ;check for zero crossing  SUB ROUTINE NOT
        call sttimer          ;start first timer             SUB
        call  tog              ;toggle outputs             SUB ROUTINE

; check timer
        movf     TMR0,w      ;move timer value to w
        btfsc     status,z     ; if not 0, goto loop
        goto     loop

; timed out, so check for end
; get here every 10ms

            decfsz     starttmr,f             ;decrement starttmr value

            goto         initmr              ; go around for next delay

; done, drop thru to stop program

stop     goto stop

;subroutines not included


;thanks once again for your help !

1999\04\15@225036 by Mike Henning

{Quote hidden}

The above should only be 25 for 250 ms

>initmr     movlw      -156
>             movwf      TMR0           ; 156 * prescaler(256) * (4MHz)
>=> 10ms approx
You're calculating using a 4 Mhz clock
The TMR runs at clock/4 = 1 microsecond per TMR tick at 4 Mhz
The above should be coded as:
initmr    movlw    .215
           movwf    TMR0

This will cause the TMR to rollover to 0 aprox. every 10.2 ms.
40 x .000256 = 10.24 ms

{Quote hidden}

You may want to use the TMR interupt flag to check for rollover.
   btfss    TMR0IF    ;If TMR0 flag is set then TMR0 rolled to 0
   goto    loop
   bcf    TMR0IF    ;clear flag
{Quote hidden}

1999\04\20@130657 by electme

Mike Henning wrote:

thanks for your help mike
i appreciate it

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