Set Operating Frequency for PIC18F4455

[anthony]

Target Frequencies:
(1) 48 MHz for CPU and Peripherals Clock
+ deriving from the 96 MHz PLL module
+ using Oscillator Postscaler: configure as divide-by-2

(2) 48MHz USB Clock
+ deriving from the 96 MHz PLL module
+ using PLL Postscaler: congigure as Fixed Divide-by-2

Oscillator: 20MHz crystal oscillator as an external clock

My Questions:
(1) How can I set these target frequencies using CCS PIC C compiler (PCH)?

(2) How can I declare the Device Specification # FUSES options? (what is the specific options? )

(3) In file 18F4455.h, where can I find the definitions of each "options" of the #FUSES as below

[Ttelmah]

Just select X4, and feed in an external 4Mhz clock.
This gives the PLL generating 96Mhz, and the default divider (/2 = 0:0 on the divider bits accessed by the PLL1, and PLL2 fuse bits - which your list does not show...). This 'defaults' to USBDIV being off, and high speed operation (at 48Mhz).
Obviously set the other fuses (watchdog, Brown out reset etc.), as you need.

Best Wishes

[anthony]

Thanks. I will try.

However, currently I do not have 4MHz clock. I have 20MHz crystal instead.

In that case, please help me for 20MHz crystal. Can I use H4 or HS? I have already tried both but failed.

[Ttelmah]

Read the chip's data sheet. For 20MHz, you need to use HSPLL (H4), with PLLDIV set to 0b100. Your version listing, does not show the PLL fuses, so I'd consider just adding the entry as a #ROM line.

Best Wishes

[anthony]

Thanks. I have downloaded new version of PCH ver3.222, showing PLL fuses.

//////// Standard Header file for the PIC18F4455 device ////////////////
#device PIC18F4455
#nolist
//////// Program memory: 12288x16 Data RAM: 2048 Stack: 31
//////// I/O: 36 Analog Pins: 13
//////// Data EEPROM: 256
//////// C Scratch area: 00 ID Location: 2000
//////// Fuses: XT,XTPLL,EC_IO,EC,ECPIO,ECPLL,INTRC_IO,INTRC,PROTECT
//////// Fuses: NOPROTECT,BROWNOUT_NOSL,BROWNOUT_SW,NOBROWNOUT,BROWNOUT,WDT1
//////// Fuses: WDT2,WDT4,WDT8,WDT16,WDT32,WDT64,WDT128,WDT,NOWDT,BORV21
//////// Fuses: BORV28,BORV43,BORV46,PUT,NOPUT,CPD,NOCPD,NOSTVREN,STVREN
//////// Fuses: NODEBUG,DEBUG,NOLVP,LVP,WRT,NOWRT,WRTD,NOWRTD,IESO,NOIESO
//////// Fuses: FCMEN,NOFCMEN,PBADEN,NOPBADEN,CCP2B3,CCP2C1,WRTC,NOWRTC,WRTB
//////// Fuses: NOWRTB,EBTR,NOEBTR,EBTRB,NOEBTRB,CPB,NOCPB,LPT1OSC,NOLPT1OSC
//////// Fuses: MCLR,NOMCLR,XINST,NOXINST,INTXT,INTHS,WDT256,WDT512,WDT1024
//////// Fuses: WDT2048,WDT4096,WDT8192,WDT16384,WDT32768,HS,HSPLL,PLL1,PLL2
//////// Fuses: PLL3,PLL4,PLL5,PLL6,PLL10,PLL12,CPUDIV1,CPUDIV2,CPUDIV3
//////// Fuses: CPUDIV4,USBDIV,NOUSBDIV,VREGEN,NOVREGEN,ICPRT,NOICPRT
////////
////////////////////////////////////////////////////////////////// I/O