Simple "backround" timer

[peterdeco1]

Hello Everyone. A while back, I asked for an easy way to program a "backround" timer. Melanie told me my code was very close to it and she posted a link to her "Olympic Timer" program. I still can't get it to work for me. Here is a simple program. I know I could put a pause 1000 and count 60 pauses but the actual program is complicated and I need a way for it to jump to "oneminutecheck" once per minute automatically - even while it is doing something else. Thank you.

'COMPILED FOR 16F73 USING 4MHZ CERAMIC RESONATOR

ADCON1 = 7 ' SET INPUTS TO DIGITAL
@ DEVICE WDT_ON, BOD_ON, PWRT_ON, PROTECT_ON
TRISA = %00000011 'RA0 & RA1 ARE INPUTS ALL OTHER PORTS ARE OUTPUTS
TRISB = %00000000
TRISC = %00000000
PORTB = %00000000 'ALL PORTB LOW
PAUSE 100 'SETTLE DOWN AFTER POWERUP

START:
LOW PORTB.0
IF PORTA.0 = 1 THEN START
GOTO WORK 'RA0 WENT LOW

WORK:
HIGH PORTB.0
IF PORTA.0 = 0 THEN WORK 'KEEP RB0 HIGH IF RA0 IS LOW
GOTO START 'RA0 WENT HIGH

ONEMINUTECHECK: 'COME HERE EVERY MINUTE TO CHECK RA1
IF PORTA.1 = 0 THEN WORKMORE
GOTO WORK

WORKMORE:
DO THIS & THAT
GOTO WORK

[jmgelba]

I won't comment of fixing your problem cos im too dumb, but you might want to turn off your code protect while playing with the code, or you are going to go through several pics rather quickly.

[mister_e]

but you might want to turn off your code protect while playing with the code,


Even if you have enabled the CodeProtect... it just prevent to read it, you can Still program your PIC.

peterdeco1, what else your PIC will do, here i don't see any part of your code that seems to do some delay job. Did you read TIMER0, TIMER1 section of your datasheet? what sbout the Elapsed timer of darrel?

[peterdeco1]

Thanks for the code protect advice but I'm using a flash PIC. I'm going to look for the Elapsed Timer now.

[Charles Linquis]

Here is some code I use in an 18F8720 using a 20Mhz Xtal, You can modify the technique to run on nearly any other part. It works best when you you need accuracy over a long period, but don't need to time over very small intervals.

'---------------------------------------------------------------------
T0CON =$87 ' Set up TMR0 prescaler with 256 divisor


LOOP:

IF INTCON.2 = 1 THEN
INTCON.2 = 0
TMR0H = $69
TMR0L = $7A
GOSUB CountTime
EndIF

'Your code goes here'

GOTO LOOP

CountTime:

Seconds = Seconds + 2
IF Seconds = 60 THEN
Seconds = 0
Minutes = Minutes + 1
.
.
.
RETURN




'-------------------------------------------------------------------------

Explanation of what is going on above:

Hardware Timer0 is set up with a 256 (/8) divisor
INTCON.2 gets set whenever the timer rolls over.
When the timer rolls over, the timer gets loaded with a value
that insures it will time out again in 2 seconds.

Your program executes normally, but exactly every two seconds
the CountTime sub is executed.

The only caveat: Your program MUST complete at least one loop every
2 seconds!

I have used a similar technique with the 16F series, but since the timers are "shorter", sometimes the maximum timeout is only 65 ms. Still, the procedure can be very useful.