Datasheet

PIC18F2420/2520/4420/4520
DS39631E-page 206 © 2008 Microchip Technology Inc.
EXAMPLE 18-1: CALCULATING BAUD RATE ERROR
TABLE 18-2: REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset Values
on page
TXSTA
CSRC TX9 TXEN SYNC SENDB BRGH TRMT TX9D 51
RCSTA SPEN RX9 SREN CREN ADDEN FERR OERR RX9D 51
BAUDCON
ABDOVF RCIDL RXDTP TXCKP BRG16 WUE ABDEN 51
SPBRGH EUSART Baud Rate Generator Register High Byte 51
SPBRG EUSART Baud Rate Generator Register Low Byte 51
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the BRG.
For a device with FOSC of 16 MHz, desired baud rate of 9600, Asynchronous mode, 8-bit BRG:
Desired Baud Rate = F
OSC/(64 ([SPBRGH:SPBRG] + 1))
Solving for SPBRGH:SPBRG:
X = ((F
OSC/Desired Baud Rate)/64) – 1
= ((16000000/9600)/64) – 1
= [25.042] = 25
Calculated Baud Rate = 16000000/(64 (25 + 1))
= 9615
Error = (Calculated Baud Rate – Desired Baud Rate)/Desired Baud Rate
= (9615 – 9600)/9600 = 0.16%