PIC micro Timer Code

Here's the minimal code to make timer 1 (a 16 bit timer) work using PICBasic.

General descriptions of PIC timer variables used to control the timer: (you should be able to use these no matter what programming language you use):

T1CON.0 is the first bit of the timer configuration byte, this bit is used to start and stop the timer.
--so--
T1CON.0=1, starts the timer
T1CON.0=0, stops the timer

TMR1H is the timer value's high byte (bits 8-15)
TMR1L is the timer value's low byte (bits 0-7)
--so--
TMR1H = 0 'resets the timer value's high byte
TMR1L = 0 'resets the timer value's low byte
--and--
MyTime.Lowbyte = TMR1L 'puts the timer's low byte in MyTime's lower 8 bits
MyTime.Highbyte = TMR1H 'puts the timer's high byte in MyTime's upper 8 bits

NOTE:
the MyTime should be declared as a word, not a byte since it has to be 16 bits long to hold the whole 16 bit timer1 value

NOTE:
When writing to or reading from the timer, it is very important in which order it is done. When reading the timer values you have to read first the LOW then the HIGH byte. When writing the timer values write first the HIGH then the LOW, this is due to complications in how the timer works.

NOTE:
when I say 'timer value' I mean a number representing the amount of time since the timer was started. To convert between real time and timer1 value units, there seems to be a 5:1 ration between timer1 units and microseconds (5000 timer1 units = 1000 microsecond = 1 millisecond)

Step 1 The code

'this code is an infinite loop.
'It will run through MamaLoop, then it will stop and
'wait until a specified amount of time (SomeNumber)
'has passed since the start of MamaLoop before continuing
'to FinishLoop.

'####################################################
SomeNumber var word
SomeNumber = 4500

MyTime var word

'====================================
MamaLoop:

T1CON.0=0 'stop the timer
TMR1H = 0 'Set the high part of the timer value to 0
TMR1L = 0 'Set the low part of the timer value to 0
T1CON.0=1 'start the timer

'do whatever you want in the loop
'....blah if, then, blahblah
'....blah if, then, blahblah
'....blah

'-----
'the EndLoopDelay will wait until a specified amount of time has passed
'since the start of the MamaLoop (when the timer value was set to 0)
EndLoopDelay:

CLEARWDT 'clear the watchdog timer (so PIC doesn't reset)

MyTime.Highbyte=TMR1H 'get part of the timer value
MyTime.Lowbyte=TMR1L 'get the rest of the timer value

IF MyTime > SomeNumber THEN 'if the timer value > than your number
GOTO FinishLoop
else
GOTO EndLoopDelay
endif
'-----
'====================================

FinishLoop:
'do something at the end of the loop
'then go back to restart the MamaLoop
GOTO MamaLoop

'####################################################

Comments

[cbr_umt]

Slam
hello every one
hope u fine
dear all


the above code is good one , i understand it . thats much simple
actualy
i want to calculate 1 second in pic 19f877a
can any one give an hint ............
nd when timer1 is overflow wht indiction we get.......


@ autther: plz place some more code for understanding
i work a lot on basic bt nt on timer

nd frequency measurement using pic is my part of project


thx

[robot1398]

do i just copy paste the code to the programming software

[instructable.com]

HI, would like to add one button to start/stop timer for the loop(toggle led + some delay) instead of fix "SomeNumber = 4500"
Need help...
Thanks...

[stienman]

This would be more informative if you included information such as: - What the relationship between the clock speed and "somenumber" is - ie, which somenumber will delay for one second at a given clock speed. - Pointers for further reading and possible problems (such as the race condition right after clearing the watchdog timer) - More explanation (the comments are fine for people who don't need this information - but beginners really need more than what you've explained) - This code assumes a lot about what state timer 1 is in when it starts. Does your compiler do some setup for that, or are you relying on a particular chip's reset state? - Which chips does this code work for? (Don't need an exhaustive list - but your title indicates that every PIC will support this code - which is untrue. Give a few part numbers for PICs you know it works on) You might give an example of a situation or problem that this could be used for. Of course you may be trying to keep it as simple as possible, in which case you really should include references to other material for further reading. -Adam

[leevonk]

what do you need to know to use a clock in real life. You have to know how to start it, how to set it, how to check the time, and how to stop it. All that information is right there, pretty explicetly. This works on any PIC that has timers. I did give an example of a situation in which it could be used. There are no points for further reading that I know of.

[sam]

Does anyone know how to do this in C?

[leevonk]

all the timer specific parts are probably the same, the timer variables are constant in each PIC, so I think no matter what programming language you use you would use the same variables:

TMR1L = 0, TMR1H = 0, resets the value
T1CON.0=1, starts the timer
T1CON.0=0, stops the timer

TMR1H is the timer values high byte
TMR1L is the timer values low byte

[leevonk]

to clear the watchdog timer in C, insert a line of assembly language to say: CLRWDT to insert assembly language into PICBasic you use an @ as in: @ CLRWDT