interrupts time doubt

[jaimechacoff]

Hi, I have a doubt about the interrupts.

My question is:

I have a done a program that reads an encoder by the portbB, actually, I changed the program that Ttelmah left, then I put a timer and I let the software count how many encoder counts can we get in 10 interrupts, then I said, ok, the speed of my motor is XXX counts per interrupt.

But where is my problem, I did that with a clock of 20MHZ, now I using a clock of 48mhz because I have changed the whole software into a RS232toUSB connection, and the counts per interrupts are the same, BUT not the counts per second, because this is how I set my timer:

USB

[PCM programmer]

I don't understand your explanation completely. I think you have stated this:

1. You have changed the oscillator on your PIC from 20 MHz to 48 MHz.

2. With the 20 MHz oscillator, the RTCC interrupts at a rate of 76 Hz.
But with the 48 MHz oscillator, it interrupts at a rate of 183 Hz.

3. Inside the #int_rtcc interrupt routine, you read a motor encoder
of some type (the type of encoder is not stated).

4. You referred to a previous post by Ttelmah. Can you provide a link
to this post ?

5. You state that the "counts per second" is not the same. Does this
refer to the "counts" from the motor encoder, or do you mean the
RTCC interrupt rate ?

6. You said you were expecting a small interrupt time. Are you referring
to the overhead (execution time) of the CCS interrupt handler ?
This handler has to "save the state of the machine" upon getting the
interrupt, and restore it upon exit. This takes time. It will take less time
with a 48 MHz oscillator.

Can you state your overall problem ? Is your problem that with a
48 MHz oscillator, the motor speed is not determined correctly now ?

Also, always post your PIC, and preferably, also post your compiler version.

[jaimechacoff]

Thanks PCM, you were right in all your points.

I could not find again the post by Ttelmah, but this is his routine: