pic18f4520 baud rate change to 115200

[caltex88]

hi guys....

right now the default is 19200...using a 4MHZ osscilator. i need 115200 baud rate for my gsm modem...rumour that i need got to change to a 20Mhz osscilator...but can i change it into 16Mhz?


and what do i've to change in the code as well

penUSART (USART_TX_INT_OFF & // Transmit interrupt ON/OFF
USART_RX_INT_ON & // Receive interrupt ON/OFF
USART_ASYNCH_MODE & // ASYNCH/SYNCH MODE
USART_EIGHT_BIT & // Transmission Width
USART_CONT_RX &
USART_BRGH_HIGH,8);


is the code right for 115200 baud rate...


thanks in advance

[Charles Linquis]

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

[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