16f54 stops running with RC OSC

[tshaffer]

These boards were made by someone else I was just reprograming them to be serial displays. HoweverI think that they are probably running at 4 MHz. haven't checked it yet
but seems to run display normaly. I have tryed to run boards with a 16F57 and same RC
values at 8 MHz seemed OK but it didn't like anything higher. Haven't tryed to go higher than 4 MHz. with the 16F54 but I suspect it woul be the same.
I have a project that i want to count the number of pulses in a span of about 2 seckonds.
The pulses go form 0 to 5 volts the attact is strait up the sustain at the top is about .25ms
then drops almost strait down to about 1.25 volts then has a decay of about 2ms to 0.
They happen at irregular intervils and may be non existant. I need to know how many times
they occur in that time span. Usualy 4 or less pulses occure but could be double or tripple
that. woUld like to use 8 pin chip. 12f683 or simular. any IDEAS

[tetsujp]

Resistor low as 472 Ohms looks suspicious to me.
Have you checked MCLR pullup resistor (for instance 4.7k)?

16f54 is specified upto 20 MHz.
I don't think 20 MHz is possible using RC.
the RC oscillator on the PICs is only designed for low frequency (some MHz at best).

There is alternative way: use RF inductor (HS mode), values low as 22uH possible but somewhere there is margin when there is no more oscillation.

Due to high tolerance/temperature affection of small ceramic capacitors, I don't use RC at all.