On Sat, 13 Jul 2002 12:03:01 -0700, Nikolai Golovchenko wrote:

<snip>

>Usually RC-oscillator is completely inside the chip,
>but a few PICs (like 16F628) have external resistor mode (ER) for the
>oscillator. The resistor is hooked between CLKIN and VSS. So, if you
>connect more resistors in parallel controlled by pins, the frequency
>could be adjusted in some range. It might be difficult to control
>since pins themselves add another variable, so the frequency could
>depend on overall power consumption of the PIC, for example...
>Alternatively, the resistors could be switched by an external device
>like analog MUX or resistor DAC. That would remove that variability.
>

Could a digital pot perhaps be used rather than external resistors and
switching hardware?=20

I'm not sure about the power implications but using one would allow
calibration to be done with just the one resistive element.


Regards, Bob

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