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