Runtime switching from INTRC to EC

[tomthkho]

Anyone has any idea how to perform clock switching from INTRC to EC during runtime? TIA

[PCM programmer]

Always post your PIC.

[tomthkho]

PIC18F4550

the current situation is we need to run two clocks, 1. internal at 1MHZ and 2. External at 40Mhz is there a method to switch between the two during runtime?

[Ttelmah]

You can change oscillators, but not the fuses.
On the 4550, you can switch from the external oscillator to the RC oscillator, using the setup_oscillator instruction. Look at section 3 of the data sheet 'power managed modes', and the constands for setup_oscillator, in the include file. For you:

setup_oscillator(INT_RC|OSC_1MHZ);
#use delay(CLOCK=1000000)

and

setup_oscillator(OSC_NORMAL);
#use delayCLOCK=40M)

with the fuses set to select the 'normal' external hardware oscillator, should give the required speeds.

_However_ some very real caveats exist. Are you using USB?. If so, and this is enumerated, there _will_ be problems if you change the porcessor clock. Also, what is your supply?. Changing _back_ to the high speed is unreliable, unless the supply meets the spec for the high speed, _before_ you implement the switch 'up'.

Best Wishes