How 2 Display Switching frequency?

ThomasC · Joined: 09 Oct 2007 Posts: 62

I've done multiple searches. I'm using a PIC16F690.

I believe my frequency current is:

#use delay(clock=4000000)

but can I display that in real time over RS232? Thank you all. Smile

Ttelmah · Guest

The only way for the chip to actually be able to detect it's own frequency, is if it has another clock source. If (for instance), you have an external 1/sec sgnal on a pin, then you can (crudely), count the number of instructions between the pin changing, or (more accurately), use a CCP module to count the clock pulses between edges.
You can't work out the frequency, without a second reference (just as, you cannot tell how 'high' you are, without some baseline to compare 'height' to). If using an external serial port, then you could generate a good estimate (if you know the baud rate of the port), by using the bit width as your reference. However at the end of the day, if you are able to send serial data, your internal oscillator frequency must be close to 'right'.

Best Wishes

amcfall · Joined: 20 Oct 2005 Posts: 44

I am a bit confused as to what you are trying to accomplish. As said above, you pretty much have to know what frequency you are running at to do any serial communications. If you don't know what frequency you are running at, how are you going to send any data out the serial port?

Avery

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Perhaps what you are looking for is a preprocessor statement like __DATE__
only for the clock instead of the DATE or a getenv(string) that would return the clock value in #use delay(clock=40000000). Your code would then have the compile time value of your clock frequency. getenv () makes a lot of values available but it doesn't make the clock value available. Even if available it wouldn't actually measure the frequency just report what you specified at compile time.

Ken Johnson · Joined: 23 Mar 2006 Posts: 197 Location: Lewisburg, WV

From the V4.060 help file, getenv("CLOCK") returns the MPU FOSC

Ken

ThomasC · Joined: 09 Oct 2007 Posts: 62

amcfall · Joined: 20 Oct 2005 Posts: 44

ThomasC · Joined: 09 Oct 2007 Posts: 62

Sorry, I confused the clock speed with the external/internal oscillator/RC oscillator connection (RA5/CLKIN).

I would like to display input from pin RA5 on the pic16F690. Thanks.