[SOLVED] how to reach maximum speed with pic18f2550

[adnan_merter]

hi,

i need to use my pic18f2550 at maximum speed during a rs232 data exchange, because it has to receive and compare some data at the same time,

now i am intended to connect a 40mhz xtal, but i just found out mazimum xtal freq. is 25 mhz for this pic.

but there is also some congfiguration for my pic to faster than 25 mhz !!!

now could you tell me about these configuration, i read the datasheet and a little lost

thanks :!:

 

[deniah]

You need to connect 10MHz xtal to PIC, and in configuration settings for xtal type choose HS-PLL. You may also need to define oscillator frequency to 40MHz.

 

[adnan_merter]

i have currently 20 mhz connected, is it possible to reach same speed wit this xtal, and could you tell me which fuses has to be set for this configuration

 

[FoxyRick]

Please read chapter 2 of the datasheet, in particular see table 2-3 which lists many possible configurations and fuse settings.

Find the row for a 20MHz source. It is evident that a system clock of 48MHz can be obtained by setting HSPLL, with a PLLDIV of 5.

Note that the 18F2550 has a maximum system clock of 48MHz - a bit faster than the usual 40MHz of other 18F PIC's.