16F877A timer to capture in microseconds

[Melanie]

Three things...

1. Try it. Build the circuit and change the pre-load value for the Timer for 1mS instead of 10mS and change the display to show the additional digit.

2. If it is too slow, try (a) connecting the LCD in 8-bit rather than 4-bit mode to reduce the display time, (b) use a 18F part at 40MHz instead of a 16F part at 4MHz, (c) The danger is you may throw data at the LCD too fast and it won't love you, so try displaying the data only every tenth count, or just at the end with the final result.

3. Consider using the CCP Module of the PIC. You will be able to capture events into the uS range with that. Datasheet of your chosen PIC will explain how to use the CCPM - naturally chose a PIC that has it!

[sycluap]

Method 1 is sufficient to complete my project, as it is possible to capture display the time in milliseconds.

I am facing a problem here of which, I do not know how to calculate the require timer pre-load value in order for to timer to count on 1 millisecond basis. I tried to apply the value $FC38 which I calculated based on my understanding from $D910 as in the sample codes, but it appears to that the timer counts become slower. I tried with other values such as $FFFE, $03C7, all seems to make the timer count really slow.

Can anyone guide/teach me in how to calculate the actual pre-load value which I can get 1 millisecond timer and display it on LCD? I am using 16F877A with 4Mhz crystal.

Sorry for all the question, I am really new to this, hope can help me. Very much thanks.

[Melanie]

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]

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]

Anyone can help me on this?

[sycluap]

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]

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

	ASM
	' your asm code goes here
	ENDASM

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

	YourVar VAR BYTE

	ASM
	' your asm code goes here
	CLRF _YourVar
	ENDASM

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