Creating timer in PIC

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #1

I want to create a timer of 25 us in PIC 16f887 and use the same timer for different functions.

Using that same timer I want to create different time intervals

If anyone has an idea please let me know

 

S

someonesdad

Joined Jul 7, 2009

1,583

Mar 7, 2011

• #2

For assembly code, look at the beginning lessons in the PICkit 2 Starter Kit user manual. A basic timer can be done in a few assembly language statements and you'd make it a subroutine. In C, you can call the _delay(us) function which delays the specified number of microseconds. Or, you can do it yourself with a busy-wait loop or use a timer and an interrupt.

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #3

Actually I have created a timer of 25 us but when I want to use that same timer to work as 10 ms timer it doesn't work

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #4

I tried to increment the variable to reach upto 10 ms but it didn't work

 

R

rmondeja

Joined Mar 7, 2011

1

Mar 7, 2011

• #5

It has been a while since I finish my last project with pics, but I'm pretty sure you can accomplish the 10 ms timer using two counters, from 25 us to 1 ms the ideal counter will be call 400 times and with 8 bits pics the maxim is 256, thats why it has to be done using two counters. The two counters products must give a result of 400, finally all this should be solved using conditionals

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #6

Which conditionals are you talking about?

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #7

I have three tasks to perform say x1, x2, x3

I want to create only a single timer of 25 us which I have done.
Next
x1 has to be performed every 50 ms
x2 has to be performed every 500 ms
x3 has to be performed every 10 ms

Please let me know if anyone has an idea

 

S

someonesdad

Joined Jul 7, 2009

1,583

Mar 7, 2011

• #8

Did you bother finding the document I told you about? It gives you the solution you're looking for; it's only a few lines of code and easy to understand.

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #9

I could not find anything related to timer in PIckit2 Starter User manual.

I know how to define the timer.

But I want the same timer of 25 us to work as 3 timers of 10 ms, 500 ms , 50 ms at the same time

I haven't yet fixed that problem

Please let me know your opinion

Thanks

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 7, 2011

• #10

If you have the link to that document, please paste here

Thanks

 

Markd77

Joined Sep 7, 2009

2,806

Mar 7, 2011

• #11

If you have the link to that document, please paste here

Thanks

Click to expand...

http://tinyurl.com/4qxoeqm

 

MMcLaren

Joined Feb 14, 2010

861

Mar 8, 2011

• #12

May I ask why you've chosen 25-usecs as your "base" timing interval? That's a very short interval. I would think a 1 or 10 msec "base" interval would be more appropriate for your 10-msec, 50-msec, and 500-msec intervals.

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 8, 2011

• #13

I am using that inteval timer because I also need the frequencies higher than 10 kHz

Where is there mention of Timer in Pickit2 manual??????

 

t06afre

Joined May 11, 2009

5,934

Mar 8, 2011

• #14

What kind of processing will you do at 10-msec, 50-msec, and 500-msec intervals. Will you just toggle som pins or run some code. That would be nice to know. I think we need more info about your project

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 8, 2011

• #15

yes I would be running some code during these time intervals

I also would like to know if it is indeed possible to run three different tasks at the same time using only one timer

Thanks

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 8, 2011

• #16

I would appreciate any help in solving this timer issue

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 8, 2011

• #17

Following is the code I tried but not succeeded

I have to use timer of 25 us

Using that same timer I have to toggle bit 5 each of PORTA,B,C after every 10 ms, 50 ms, 500 ms respectively

#include <p16F887.inc>

org 0
Start:
goto SOC
org 4
goto ISR

SOC:
call Bank0
call Bank1
bcf INTCON,2
bsf INTCON,5

ISR:
btfsc INTCON,2
goto label1

label1:
movlw b'00100000'
xorwf PORTA
Bank0:
movlw 0xFB
movwf TMR0
return
Bank1:
BSF STATUS, RP0
movlw 0x61
movwf OSCCON
movlw 0x00
movwf TRISA
movlw 0x00
movwf TRISB
movlw 0x00
movwf TRISC
movlw 0x00
movwf OPTION_REG
BCF STATUS,RP0
return

End

 

Last edited: Mar 8, 2011

blueroomelectronics

Joined Jul 22, 2007

1,757

Mar 8, 2011

• #18

Your code needs work, your main code just runs right into your interrupt routine, no retfie, no clearing the IF flag.

Try running with the MPLAB simulator. You could see what's happening while single stepping through your code.

 

R

Thread Starter

RG23

Joined Dec 6, 2010

304

Mar 8, 2011

• #19

I included retfie now
#include <p16F887.inc>

org 0
Start:
goto SOC
org 4
goto ISR

SOC:
call Bank0
call Bank1
bcf INTCON,2
bsf INTCON,5

ISR:
btfsc INTCON,2
goto label1
retfie
label1:
movlw b'00100000'
xorwf PORTA
retfie
Bank0:
movlw 0xFB
movwf TMR0
return
Bank1:
BSF STATUS, RP0
movlw 0x61
movwf OSCCON
movlw 0x00
movwf TRISA
movlw 0x00
movwf TRISB
movlw 0x00
movwf TRISC
movlw 0x00
movwf OPTION_REG
BCF STATUS,RP0
return

End

 

blueroomelectronics

Joined Jul 22, 2007

1,757

Mar 8, 2011

• #20

Single step through your code in the simulator. Putting your main code after the interrupt routine is traditional. There are several mistakes in your coding.