PIC 18f46j53 internal clock and USB low speed

[zcetrt]

Hi to all.

I am trying to connect PIC 18F46J53 via low speed USB. I want to use 16MHz internal clock. If I understand it correctly, I have to set fuse bit LS48MHZ. But there is no option in CCS compiler.

How can I set the fuse #FUSES LS48MHZ to make USB low speed work with internal 16MHz clock?

I am using CCS 4.114 compiler embeded in MPLAB.


Thank you for your help!

[Ttelmah]

I don't see the 'internal 16MHz clock. I presume you mean you want a 16MHz CPU clock?.

Looking at the oscillator diagram, you need to use the 8MHz master output from the oscillator block. This has to be selected to feed to the PLL (INTRC_PLL). Then the PLL has to be set to divide this by 2 to give 4MHz (PLL2). You then have to select the PLL output (PLLEN), so you have 48MHz feeding to the USB selector, and LS48MHZ, should then divide this by eight to give the required 6Mhz to the USB.
If you then want a 16MHz CPU clock, you would want CPUDIV3.

Setting these fuses, then compiling, and loading the code with MPLAB, shows the required fuses all set correctly that I can see.

Best Wishes