Expanding Timer1 counting range

[sycluap]

I use Timer1 as a free running timer, using 4Mhz clock and 16F877A MCU. I do not know how to extend the timer range as it is from 0 to 65536 microsecond using 4Mhz clock.

Can anyone teach me to extend the timer range from 0 to 5 seconds?

Thanks in advance.

[Acetronics2]

Hi,

Hardw.solution : Just use the external TMR1 clock with a 32,768 Hz Xtal ... easily gives 1 count per ms !!!

SoftW.Solution : increment a variable for each overflow ( interrupts using or polling the overflow bit TMR1IF )

Also See Darrel's posts about instant interrupts ... The Hardw solution is described here !!!

Alain

[sycluap]

I am using 4MHZ, 16F877a, Timer1, setting TMR1H = $00 and TMR1L = $00. Tried to activate the timer as free running timer. Previously used to capture the timer time from 0 - 65536 microseconds (full range). Now that I am trying to extend the timer range and to respond to 1ms interval, I change the TMR1H = $FC and TMR1L = $18, with the codes below to capture the timer1 overflow.

Looping:
While PIR1.0=0
Wend
PIR1.0=0
TimerOverflow=TimerOverflow+1
LCDOUT $FE,$C0,DEC5 TimerOverFlow
If ButStop = 1 Then goto StopTimer
Goto Looping

But I am unable to get in 1ms interval. Can anyone guide me on this?

[Acetronics2]

You just need to preload Timer 1 with a value "not so far" from 65536 - 1000 ... no more free running timer usable !!!

it will overflow for 1000 counts = 1 ms ...

"not so far" mean you have to add the time to reload the timer and do what you want to the "64536" value ...

See Steve's ( Mr E !!! ) calculator here : http://www.mister-e.org/pages/utilitiespag.html


I also forgot you could use the "compare" function of the CCP module ... and poll the CCPIF bit !

Alain

[sycluap]

Yeah, I did make TMR1H = $FC, TMR1L=$18, which is obtained from 65536-1000. But the timer does not give me 1ms interval. I do not know what is wrong. Below is my program:

'MAIN PROGRAM
'------------
ResetTimer:
GoSub SetReg
LCDOUT $FE, 1
Timer1H = 0
Timer1L = 0
Result = 0
TimerOverflow = 0

Main:
LCDOUT $FE, $80, "Test Mode 1"
LCDOUT $FE, $C0, "Visual Response Test"
If ButStart = 1 Then goto StartTimer
Goto Main

StartTimer:
LCDOUT $Fe, 1
LCDOUT $FE, $80, "Calculating..."
T1CON.0=1

Looping:
While PIR1.0=0
Wend
PIR1.0=0
TimerOverflow=TimerOverflow+1
LCDOUT $FE,$C0,DEC5 TimerOverFlow
If ButStop = 1 Then goto StopTimer
Goto Looping

StopTimer:
T1CON.0 = 0
LCDOUT $Fe, 1
GoSub GetValue

DisplayResult:
Result = TimerOverflow
LCDOUT $FE,$C0, dec5 Result
If ButStart = 1 Then goto StartTimer
If ButReset = 1 Then goto ResetTimer
goto DisplayResult


'SUBROUTINES
'===========
'Reset Timer1 Register to Start from 1ms interval
'-------------------------------------------------------
SetReg:
TMR1H = $FC
TMR1L = $18
Return

Is there anything wrong with the program that cause the Timer unable to display 1ms interval timing on LCD?

[Acetronics2]

Your LCD display is unable to show time for EACH ms ... the LCDOUT command needs much more thant 1 ms - OR you should use LED Display ...

With that way of programming You might have enough time to refresh the display between two interrupts ...

Here, to be accurate ... you just can display exact time ONLY once timer stopped !!!


see How Darrel's "Elapsed timer Demo " works ... and you will be able to see "intermediate time"

http://www.picbasic.co.uk/forum/show...=Elapsed+timer


Alain

PS: you can read the ms "on the fly" .... Wooowww !!! you got a fantastic pair of eyes !!!
LOL ...