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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| USB and Crystal frequency |
 Posted: Mon May 23, 2011 1:03 pm |
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Colleagues,
I wrote a working code based USB HID example (fuses that set the clock are below). USB host successfully enumerates my device if it has 20MHz crystal (xtal).
| Code: | #include <18F2550.h>
#device ICD = TRUE
#fuses HSPLL, NOWDT, NOPROTECT, NOLVP, NODEBUG, USBDIV, PLL5, CPUDIV1, VREGEN
#use delay(clock = 48000000)
#define USB_HID_DEVICE TRUE
// ... |
How can I make it work with 12MHz crystal? If I simply install a 12MHz crystal, USB host doesn’t enumerate my device, although the rest of the firmware runs (with slower timing, of course).
I bet, this subject came up in the forum before, but I couldn’t find those threads.
Any suggestion, insight or reference is really appreciated!
Cheers,
- Nick
_________________
Read the label, before opening a can of worms. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 23, 2011 1:11 pm |
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| Quote: |
USB host successfully enumerates my device if it has 20MHz crystal.
#include <18F2550.h>
#device ICD = TRUE
#fuses HSPLL, NOWDT, NOPROTECT, NOLVP, NODEBUG, USBDIV, PLL5, CPUDIV1, VREGEN
#use delay(clock = 48000000)
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The PLL requires a 4 MHz input. The fuse shown in bold is the pre-scaler.
20 MHz / 5 = 4 MHz. Look in the 18F2550.h file to see other available
pre-scaler values for that fuse. |
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