1

Is it possible to use USB on pic18f4550 without an external crystal? I'm trying to run "HID Read Write Interrupt" example (from mikroC) but I don't have an oscillator (I have tic 3.579545mf which seems to be of no help). How can I configure my microcontroller to use internal oscillator for USB? The datasheet is too complicated for me now, I can't even understand if it's possible at all.

I also have pic12f683, can I use it instead of the crystal?

grabantot
  • 2,111
  • 20
  • 31

2 Answers2

3

Unfortunately, no, it is not possible to use USB on PIC18F4550 without an external crystal. Other PICs in the 18F family provide this capability. But the PIC18F4550 datasheet section 2.2.5.1 Internal Oscillator Modes states “When the internal oscillator is used as the microcontroller clock source, one of the other oscillator modes (External Clock or External Crystal/Resonator) must be used as the USB clock source.”

And I don't see an easy way to use the PIC12F683 as the external oscillator source. It has an 8 MHz internal oscillator (HFINTOSC) that can be configured to output FOSC/4 output on the OSC2 pin, which is 2 MHz. But going back to the PIC18F4550 datasheet TABLE 2-3: OSCILLATOR CONFIGURATION OPTIONS FOR USB OPERATION the lowest Input Oscillator Frequency is 4 MHz.

jolati
  • 700
  • 11
  • 19
1

Try this device, which has an internal 48Mhz oscillator for direct configuration and support of USB2.0 fullspeed :

PIC16F1459

Jean-francois
  • 316
  • 1
  • 9