arduinocameraoscillatorpwmstm32
I want to use the simple camera ov7670 and that camera requires a system clock, called XCLK.
The clock requries 24 MHz input from a source that are at 50% duty call and a period of 24 nanoseconds.
Does this mean that I should use a PWM signal from a micro controller, or should I use an external crystal oscillator?
You are interested in the relative error and/or stability, which is unaffected by any division. So, other things being equal, take the lowest ppm clock source for the best accuracy.
If 50 ppm is enough for you, I would choose the crystal for board space and price.
For better accuracy you could consider a better quality (tuned) crystal oscillator. Same physical format as a regular oscillator (14-pin DIP size), but higher price (~ $20).
Yes, the 16F84 does need an external oscillator. It is a very old PIC.
However almost all of the newer PICs have an Internal RC Oscillator that can be selected, which will be mentioned in the datasheet.
I would really consider getting hold of a newer PIC, something like a 16F690, or 16F1824/16F1828. These are far more current, and can do anything the 16F84 can do and much more.
If you want to use your 16F84 though, either use an external clock (e.g. from 555 timer or oscillator based on e.g. an inverting gate with RC or crystal) or crystal as specified in the datasheet, or if you don't have an external clock or crystal use the RC option.
Best Answer
You should use an external Crystal Osc. (XO) with the duty cycle specifications given. That will satisfy the pulse width variations given for the range of frequencies also given.