16F877A timer to capture in microseconds

**Melanie** · - 19th December 2007, 16:18

And you changed the TickCount Interrupt Handler to account for the fact that Hundredths are now Thousandths and changed the variable from a byte to a word and ensured everything is ticking in 1mS steps? Or have you just changed the pre-load valve and hoped everything would work?

**sycluap** · - 20th December 2007, 02:54

I only made changes to the pre-load value, LCDOUT command to display up to 3 digits and the tickcount interrupt handler, where I put in the new:

Tickcount changes:
If RunningFlag=1 then
Thousandths=Thousandths+1

If Thousandths>9 then
Thousandths=0
Hundredths=Hundredths+1

etc....

LCDOUT Changes:
LCDOUT $FE, $C0, DEC3 Thousandths, " Thousandths"

It doesn't seems right. What went wrong? Did I miss out anything? Getting 1ms counts is very critical for my project, but I just couldn't figure it out.

**sycluap** · - 22nd December 2007, 06:36

Anyone can help me on this?

**sycluap** · - 10th January 2008, 05:24

Is there anyway to add assembly language to the codes in PicBasic Pro? Can anyone guide me to do polling using timer 1 in 1ms interval?

**mister_e** · - 10th January 2008, 05:37

Yes it's possible to mix assembler. you just need to use ASM/ENDASM

Code:

	ASM
	' your asm code goes here
	ENDASM

Unless you define your variable as SYSTEM var, your PBP variable must have an underscore before them

Code:

	YourVar VAR BYTE

	ASM
	' your asm code goes here
	CLRF _YourVar
	ENDASM

And PBP don't appreciate BANKSEL. you must use CHK?RP instead

**sycluap** · - 10th January 2008, 08:14

thanks mister_e, this will help me in experimenting the 1ms interval polling. Is there anyone can help me on how to get 1ms interval by polling method for timer1?

**sycluap** · - 12th January 2008, 07:02

I modified the Olympic Timer program, by replacing the:
TMR1RunOn.HighByte= $FC
TMR1RunOn.LowByte=$18

and deleted the TMR1RunOn=TMR1Preset+TMR1RunOn, to directly load the TIMER1 preset value into the timer1 register.

This make the timer by the program runs faster than used to. Until I change the value to $FF,$FE, the timer can have the timing interval very close to 1ms, but still slightly delayed, as I compare the timing (seconds) with a watch. The watch is about 2x faster than the timing by the timer.

Attached is the code I wrote by referring to the Olympic Timer by Melanie. Is there any problem with the code? Any solution for that? Thanks in advance.