Dual clock speeds on a PIC

[paul borgmeier]

I have to accurately measure the frequency/rate of some events so RC oscillators are out of the question during the measure phase.

Another Approach? - The 18F4620 can be clocked by switching from an external XTAL on OSC1 and OSC2 to a 32kHz XTAL on TMR1. See section 3.3.2 of the data sheet for details (from the data sheet “This gives users the option of lower power consumption while still using a high-accuracy clock source.)

[tenaja]

An even faster way to save battery power--without even changing the bulk of your code--is to use a different PIC! The 18F4620 was NOT designed for long battery life. At 4MHz with INTOSC, it takes 1.3mA at 3.0v. There are PIC's that will do the same speed with only .58mA draw--well under 1/2 the power draw. With careful data sheet scrutiny, you should be able to find one that runs 1MHz with even less power.

You will almost double your battery life by going from 5.0 to 2.7v.

I have a friend who runs their systems for years on one battery... he has 8 or 9 voltage regulators in the system so each circuit is individually powered, and totally shut down when not in use. Yes, it is expensive, but it is very efficient.

You are trying to cram a V8 engine into a Toyota Echo so you can enter a stock car race... but there are much easier and better ways to do it. Your multiple oscillators just seems like more work than it'd be worth, considering all of the other options available. Especially when 18F's already allow you to run an external crystal or the internal osc.