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LetThereBeLight
Joined: 15 Jul 2007
Posts: 3
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| 18F2455 FUSE OSCILLATOR & USB |
 Posted: Sun Jul 15, 2007 5:57 am |
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Hi all,
i have a little question, i use a PIC 18F2455 for USB communication between my device and USB. I use a 20 MHZ quartz oscillator with thoses fuses :
| Code: | #fuses HS,PLL5,USBDIV,NOWDT,NOPROTECT,NOLVP,NODEBUG,VREGEN,NOMCLR,NOIESO,NOSTVREN,NOPUT
#use delay(clock=20000000) |
it works perfectly .
I xwould like to speed up my PIC and use a 48 MHz quartz , i use thoses fuses with this quartz :
| Code: |
#fuses HS,PLL12,USBDIV,NOWDT,NOPROTECT,NOLVP,NODEBUG,VREGEN,NOMCLR,NOIESO,NOSTVREN,NOPUT
use delay(clock=48000000)
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in this case the PIC is still working but not the USB. so i check the datasheet, i looks like for 48 MHz you cannot use a Crystal but an EC oscillator type ?
am I wrong ? what should i change with the fuse to get USB working at full speed ? |
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Ttelmah
Guest
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| Posted: Sun Jul 15, 2007 7:18 am |
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Use the original quartz, and:
| Code: |
#fuses HSPLL,PLL5,USBDIV,NOWDT,NOPROTECT,NOLVP,NODEBUG,VREGEN,
NOMCLR,NOIESO,NOSTVREN,NOPUT,CPUDIV1
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'HSPLL', means use the HS oscillator, but take the CPU clock from the USB PLL output (96MHz). You then add the CPUDIV fuse to specify the division (/1). The USB clock is automatically divided by 2 before being fed to the CPU divider, so you get 48MHz to the CPU.
The maximum frequency for the external oscillator, is 25MHz.
Best Wishes |
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LetThereBeLight
Joined: 15 Jul 2007
Posts: 3
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| Posted: Mon Jul 16, 2007 1:29 am |
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| thank you |
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