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i have been working on a datalogger project that requires
recalibration of a timing loop based on outside temperature.  Chip is
16c84.  i created a small program to
setup the wdt
clear a counter
clrwdt
run a loop till timer times out
display answer on leds at portb
go to sleep
start over.

im attaching the code.  .

heres the problem:  it doesent work.  when wdt trips, it goes back to
top, instead of being routed to display routine, it reinitializes the
count register, and basically orbits between the loop and
re-initialization.  playing around with it, i cant find evidence that
the wdtimeout really clears bit 4 in status.  as you can see from the
code, i tried testing bit 4 first, then bit 3,, then the other way
around.  i tried catching it after the initialization.  i tried to
catch it by using the presence of data in the count register to goto
the display routine.  i have confirmed that the routine at the top
does implement restart (status,4=1 and status,3=1) ok, sleep looks
ok, and mclr looks ok.  but wdt doesent seem to work...

im using most recent (dos) mpasm on old 486 laptop.

and what will happen if this is in a subroutine?  the thought scares
me.  wakeup on sleep just continues with program counter, wdtimeout
loses the stack???  i stayed home from work yesterday to work on this
and im stumped.

any help appreciated.
alice

alice

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;======pict7.asm============1 aug 98===============
        list    p=16c84
        radix   hex
;----------------------------------------------------
;cpu equates (memory map)
portb   equ     0x06
mine    equ     0x0a
mflag   equ     0x0b
check   equ     0x0c
temp    equ     0x0d
status  equ     0x03
tmr0    equ     0x01
intcon  equ     0x0b
optreg  equ     0x81
trisb   equ     0x86
on      equ     1
to      equ     4
pd      equ     3
w       equ     0
c       equ     0
f       equ     1
z       equ     2
rp0     equ     5
;----------------------------------------------------
        org     0x000
;        btfss   status,4    ;timeout
;        goto    to0ck        ;=0
;        goto    to1ck        ;=1

;to0ck   btfsc   status,3    ;powerdown
;        goto   display      ;to=0&pd=1=wdt
;        goto   go           ;to=0&pd=0=sleep

;to1ck   btfss   status,3
;        goto    display         ;to=1&pd=0  mclr (could use for serial?)works
;        goto    start           ;to=1&pd=1 startup  ...works

        btfsc   status,3       ;-pd?
        goto    test1           ;pd=1  means pu or clwdt
        goto    test2           ;pd=0  set by sleep
        org     0x005

test1   btfsc  status,4        ;pd=1,to? clrwdt sets to=1
        goto   start            ;to=1& pd=1->powerup ....works
        goto   go       ;display          ;to=0&pd=1->wdt  ??????????

test2   btfss   status,4       ;pd=0,to=?
        goto   go            ;pd=0&to=0 ->sleep ???????
        goto   display          ;pd=0&to=1 ->mclr ...works

start
        movlw   b'00000000'     ;load W with 0x00
        tris    portb
      ;  clrwdt                  ;to=1&pd=1  this prevents wdt in go
        movlw   b'11011000'     ;wdt=1&1:1...timeout is 18 ms
        option
        bcf     status,rp0      ;back to bank0
        movlw   0x00               ;?????????????
        movwf   mine            ;put something in mine to start
;        clrf    portb           ;all lines low
        movlw   b'00000111'     ;bsf portb,0
        xorwf   portb           ;is this looping?
;        goto    display

go     ; clrwdt
        movfw   mine            ;if wdt then mine has count in it
        sublw   0x00               ;is it empty?
        btfss   status,z        ;z  well,does it?
        goto    display         ;cool.  show me

calib   clrwdt                        ;at this point prescale is 0
cycle                           ;time 1 wdt cycle
     ;   incf    mine,f          ;1 tick
     ;   movlw   b'00000010'     ;bsf portb,0
        movfw   status
        movwf   portb
        xorwf   portb           ;is this looping? ...yes,but....
        goto    cycle           ;2 ticks       5 total here
        bsf portb,6             ;never gets here if wdt

display; clrwdt                  ;show mine if wdt handled right
        movfw    mine
        movwf   portb           ;did it count??
        clrf    mine            ;setup for next run
        bsf     portb,2
        goto    snooze          ;all done

snooze ; clrwdt                 ;po=1&pd=1
;        movlw   b'11011111'    ;reset prescaler for long sleep
;        option
;        bcf     status,rp0
        sleep                   ;pd=0,to=1.  pgm continues...
        clrwdt
        bcf     portb,2
        movlw   b'11011000'
        option
        goto   go               ;loop
;---------------------------------------------------

        end
;------------------------------------------------------
;at blast time, select:
;       memory unprotected
;       watchdog timer disabled (default is enabled)
;       standard xtal using 4 mhz
;       powerup timer on
;======================================================