I have an odd little problem, I'm hoping one of you could shed some light on it before I spend hours tracking it down.
I'm working on a board with a PIC18F8722. We're setting it up to work in external clock mode with a 40MHz clock. This clock is, in turn, sourced by an integrated oscillator module from ECS (ECS-8FM).
The problem that we're seeing is that sometimes the thing comes up going very slowly. I haven't measured timing yet, but it appears to be running about 5x or 10x slower than it should. The problem is somehow related to the power source, with faster rise times on the power supply inducing it much more often. The only lead that I have on it right now is that with a sharp-rising power supply the oscillator takes several milliseconds to start up.
I'm wondering if the PIC 18 senses that the clock isn't present coming out of reset and defaults to an internal clock. This seems screwy, but it makes a twisted kind of sense. IIRC the oscillator is billed as working at 3.3V, so with a slowly-rising VCC it would presumably (possibly?) start working before the processor came out of reset.
Has anyone seen anything like this before, or am I on my own?