16F877A timer to capture in microseconds

[sycluap]

I tried on the OLYMPIC TIMER project provided by Melanie in the Sample Code Section, and that is indeed a good one. But, I am currently working on a project which requires me to capture the time in microseconds. While OLYMPIC TIMER project is able to display 1/100 seconds and with 4Mhz clock it will be 1 microsecond ticking.

I would like to know if there is any possibilities that I can utilize that 1us ticking to capture the time difference in microseconds and display it on LCD?

Can any experts guide me in this problem? Thanks in advance!

[sycluap]

Perhaps capture the time in microseconds is impossible to do so since no reply from anyone. Anyhow, from the Olympic Timer and Automatic Clock provided by Melanie and Darren, both of the project display the fastest time count of 10ms on LCD.

Is there any possibility that to display 1ms timer counts on LCD? Meaning that the Stop Watch Timer can capture up to 1ms instead of 10ms.

Please help me on this matter, urgent. Anyone?

[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.