Umm.. So how can I tell if my external crystal is being used?

txmarsh

major newbie question alert!... how can I actually verify that my external crystal is being used instead of the prop's internal timing circuit?
Thanks!
Tim

Bobb Fwed

Timing would be easy enough. Start up a frequency synthesis object and see if the output is correct (within a percent). The internal oscillators have massive swings from temperature and whatnot.

Another way is to look at the software. It won't be used unless specifically called out.

MicrocontrollerGuy

This might be totally wrong, but here is how I would do it:

• Remove the crystal from the circuit (so probably pull it from the breadboard)
• Verify that the Propeller does not work in this case
• Change the _CLKMODE constant to RCFAST
• Verify that the Propeller starts working again
• Put the crystal back in the circuit
• Change the _CLKMODE constant back to whatever it was (usually XTAL1 + PLL16X in most programs, which yields 80 MHz with a 5 MHz crystal)
• Verify that this still works

As you can see, this process is intended to verify that the crystal's presence or absence has an effect on the Propeller. If you verify that, you have verified that the crystal is indeed being used.

txmarsh

Hey... I like both of those ideas... thanks!
Tim