Timer using Picbasic Pro

[Melanie]

Datasheet! *sigh*

Timer1 ticks every 1uS @ 4MHz.

It's 16 bits wide, therefore with a 4MHz clock will time 65.536mS between each Flag.

Using the 1:8 prescaler your maximum time is 8*65.536mS=524.288mS

So unless Microchip has shoved hardware into your PIC that mine doesn't have, the answer is NO, Timer1 will NEVER tick 1 second @ 4MHz.

You can always use a Bit Variable as a Flag... If BitFlag=0 and Timer1Flag then half a second has elapsed - so Set the BitFlag. If BitFlag=1 and Timer1Flag then one second has elapsed, so reset the BitFlag and start over for a new Second.

Homework: What has Timer2 got that Timer1 doesn't have?

[peterdeco1]

Timer2 has a prescaler and a postscaler. Am I right Melanie, am I right??

[Melanie]

Yup, you're right... Homework Part Deux: Which now means what's the maximum Time you can let Timer2 run for at 4MHz with all the prescalers and postscalers enabled?

[peterdeco1]

Boy - you're putting me through the mill. I come up with 16.777 seconds. Am I right... am I right??

[Melanie]

Close, but no cigar...(we're talking about Timer2 in a PIC16F876/877)...

[sjohansson]

Hi Melanie.

Im working with a 18f4550 and using USB to communicate with a Visual basic program.
I need to measure the time an input pin is activated.
Normaly I use Pulsin but the USB commands must be polled every 1ms to keep contact with the computer. So how can I write a code that doesnt "halt" the program during the measuring?
The performance must be the same as Pulsin, 2us reolution at 20Mhz and it would be great if I can measure up to 500ms instead of 130ms like Pulsin.

Thanks in advance.

Stefan.

[Melanie]

I would use say CCP1 pin of the PIC and confiure the CCP Module in Capture Mode. In this mode, the module will capture the 16-bit value of the TMR1 Register when the CCP1 pin changes state. This will occur with minimal intervention from your program. The resolution at 20MHz will be in steps of 200nS to a maximum of 16 bits - ie 13.1mS. Use the integral Hardware of the PIC to help you with this one. Unfortunately you're limited to the size of the TMR1 register. Alternatively, you can use instant interrupts in conjunction with TMR1 to give you longer time periods if you enable the prescaler. Without knowing what's going on in your application it's difficult to recommend.