Calculating time delay between two inputs?

[grimmjow]

Yes i do not have obligation to use f84, and i know f877 has Timer1(16bit). Let us check this;

i will use 4MHZ xtal and f877, and it has 16 bit timer ~= 66ms is more than enough for me.

So i do not need to use watchdog timer prescaler commands and i just need to use,

OPTION_REG.5=1 and OPTION_REG.5=0 commands for timer right?

[grimmjow]

i've looked up f877 datasheet and TMR1 has its own control register (we can enable and disable it) and it's two paired (TMR1H and TRM1L)

i am not sure but this is algorythm as i understand, if TMR1L=255 then TRM1H=TMR1H+1

and if i sum them up, timepassed=TRM1H*255+TMR1L i can find time in useconds.

Thanks for your helps.

Yes i do not have obligation to use f84, and i know f877 has Timer1(16bit). Let us check this;

i will use 4MHZ xtal and f877, and it has 16 bit timer ~= 66ms is more than enough for me.

So i do not need to use watchdog timer prescaler commands and i just need to use,

OPTION_REG.5=1 and OPTION_REG.5=0 commands for timer right?

[HenrikOlsson]

Ioannis,
Thanks for catching the typo! As for the prescaler not clearing, I actually thought about that but the datasheet says that writing to TMR0 does clear the prescaler (when it is assigned to TMR0) so it shouldn't be an issue. Now, with the '877 it's of little importance anyway.

grimmjow,
Yes, TMR1 on the 'F877 is controlled thru its own control register and you get its 16bit value almost like you shown:

timepassed = TMR1H * 256 + TMR1L

Make sure you stop the timer before reading it or you MAY get weird results if the low byte happens to roll over between you reading it and the high byte.

And no, you don't need to use any prescaler since the 16bit wide timer allows you to measure 65535us which is far more than you need.

Good luck!
/Henrik.

[grimmjow]

Thanks a lot for your helps, HenrikOlsson and Ioannis.

It is great for beginners to ask pros like you. i will try these codes and im pretty sure that it'll work. I'll let you know if i have problems about some parts again.

Have a nice day.

[Ioannis]

Henrik: I missed that part about the prescaler on F84. Good one!

grimmjow:

remember to declare timepassed as a word variable.

Given that you will still be using 4MHz crystal, the timer step will be 1usec.

Ioannis

[grimmjow]

Henrik: I missed that part about the prescaler on F84. Good one!

grimmjow:

remember to declare timepassed as a word variable.

Given that you will still be using 4MHz crystal, the timer step will be 1usec.

Ioannis

Thank you Ioannis, i'm using it as word.

Btw circuit works fine thnx for your efforrs both Ioannis and HenrikOlsson