pic18f4520 baud rate change to 115200

[caltex88]

115Kbaud with a 4MHz XTAL is tough. Because the divisor has to be an integer, you can get only within 3.55% of the exact baud rate. That error is probably a bit too much. Look at the datasheet table 18-3.

20Mhz works much better. That gives you a 1.36% error. Small enough to work well.
In this case, set BRGH = 1 and SPBRG = 10

what about 16Mhz XTAL

[mister_e]

With 16 MHz the best error Percentage you'll get will be -0.79% witch is usually fair enough.

This assume you're aware that you MUST use the 16 bit baudrate generator for that.

Now to set it in C... it's your problem In PicBasic Pro

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 34  ' 115200 Baud @ 16MHz, -0.79%
SPBRGH = 0
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator

My PicMultiCalc should help you a little bit
http://www.mister-e.org/pages/utilitiespag.html