clocks

[Felix]

with ZPUino thing, is it possible to fake a 4MHz clock to feed into a PIC?

 

normally its 2 caps and a crystal feeding osc in/out

 

like this::

 

[alex]

Read the PIC data sheet. It should tell you which pin you can feed a digital clock if you don't want to use a xtal. Normally one of these pins would be an input and the other is the output of the internal xtal driver.

[Felix]

thing is, the pic is already programmed.  i am trying to interface into it without modifying its program.

 

i just don't know if its possible to run zpuino and generate a 4MHz clock with zpuino at the same time.

 

heck i dont even know if its possible to *accurately* generate a 4MHz clock with zpuino by itself.

 

i would think not, but i figure it doesnt hurt to ask.

 

i will most likely wait for my caps/xtal to come in the mail in a few days and do it that way, but was hoping for

an all in one solution.  short of adding in a 2nd pic just for clock which would be kind of dumb

[alvieboy]

Felix:

 

the best way to generate the 4MHz clock is to program the 16-bit timer w/o prescaler to provide a 50% duty cycle PWM.

 

From top of my head, set the CMP to 23 ((96000000/4000000)-1), and set the CMPLOW of the relevant PWM output to 0, and CMPHIGH to 12.

 

I can write a simple sketch that does this for you later today, if you are kind enough to tell me to which FPGA pin you'll be expecting the clock output.

[alvieboy]

Side note: the 4MHz clock will be >99% accurate. The only innacuracy can come from the board oscillator (32MHz), and even then the internal PLL will probably reduce the skew and jitter a lot.