timer/counter questions

[aratti]

Robert, without an ISR the timing is not very precise but you can try the following:


'-------------- set the registers -------------------------------
T1CON = %00111101 ' set timer1 as timer with prescaler 1:8
PIE1.0 = 1 ' enable interrupt on overflow
PIR1.0 = 0 ' clear interrupt flag
TMR1L = 220 ' 100 millisecs overflow
TMR1H = 11 ' 100 millisecs overflow
W_Count VAR WORD
'-----------------------------------------------------------------

Poll in the approriate point, somewhere in your program:

If PIR1.0 = 1 THEN
T1CON.0 = 0
PIR1.0 = 0
TMR1L = 220
TMR1H = 11
W_Count = W_Count +1
T1CON.0 = 1
endif

IF W_Count = 300 then
W_Count = 0
Do your job since 30 seconds have been elapsed..
endif

You can trim the 300 to better achieve the 30 seconds delay. (300 x 100 millisecs = 30 seconds)

Cheers

Al.

[Dave]

Robert, If I were you I would look at replacing the OLD 16F877 with something like an 18F4620. If you are using the 40 pin dip package it should drop right in and the part has LOTS more program memory space and Eeprom. Just about all I use these days is the 18F2620 as I don't need all the pins but it has the same amount of memory. Just a thought....

Dave Purola,
N8NTA