PIC18LF452 Microchip Technology, PIC18LF452 Datasheet - Page 170

• Manufacturer Part Number: PIC18LF452
• Description: (PIC18LFxx2) Enhanced FLASH Microcontrollers
• Manufacturer: Microchip Technology

PIC18FXX2
16.1
The BRG supports both the Asynchronous and Syn-
chronous modes of the USART. It is a dedicated 8-bit
baud rate generator. The SPBRG register controls the
period of a free running 8-bit timer. In Asynchronous
mode, bit BRGH (TXSTA<2>) also controls the baud
rate. In Synchronous mode, bit BRGH is ignored.
Table 16-1 shows the formula for computation of the
baud rate for different USART modes, which only apply
in Master mode (internal clock).
Given the desired baud rate and Fosc, the nearest inte-
ger value for the SPBRG register can be calculated
using the formula in Table 16-1. From this, the error in
baud rate can be determined.
EXAMPLE 16-1:
TABLE 16-1:
TABLE 16-2:
DS39564B-page 168
Legend: X = value in SPBRG (0 to 255)
TXSTA
RCSTA
SPBRG
Legend: x = unknown, - = unimplemented, read as '0'. Shaded cells are not used by the BRG.
Desired Baud Rate
Solving for X:
Calculated Baud Rate
Error
Name
SYNC
0
1
USART Baud Rate Generator
(BRG)
X
X
X
Baud Rate Generator Register
CSRC
SPEN
Bit 7
BAUD RATE FORMULA
REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
(Asynchronous) Baud Rate = F
(Synchronous) Baud Rate = F
CALCULATING BAUD RATE ERROR
Bit 6
RX9
TX9
= F
= ( (F
= ((16000000 / 9600) / 64) – 1
=
=
=
=
=
=
[25.042] = 25
16000000 / (64 (25 + 1))
9615
(Calculated Baud Rate – Desired Baud Rate)
(9615 – 9600) / 9600
0.16%
OSC
BRGH = 0 (Low Speed)
SREN
OSC
TXEN
Bit 5
/ (64 (X + 1))
/ Desired Baud Rate) / 64 ) – 1
Desired Baud Rate
SYNC
CREN
Bit 4
ADDEN
Bit 3
OSC
OSC
—
/(64(X+1))
/(4(X+1))
BRGH
FERR
Bit 2
Example 16-1 shows the calculation of the baud rate
error for the following conditions:
• F
• Desired Baud Rate = 9600
• BRGH = 0
• SYNC = 0
It may be advantageous to use the high baud rate
(BRGH = 1) even for slower baud clocks. This is
because the F
baud rate error in some cases.
Writing a new value to the SPBRG register causes the
BRG timer to be reset (or cleared). This ensures the
BRG does not wait for a timer overflow before
outputting the new baud rate.
16.1.1
The data on the RC7/RX/DT pin is sampled three times
by a majority detect circuit to determine if a high or a
low level is present at the RX pin.
OSC
TRMT
OERR
Bit 1
= 16 MHz
SAMPLING
OSC
RX9D
TX9D
Bit 0
/(16(X + 1)) equation can reduce the
Baud Rate = F
BRGH = 1 (High Speed)
0000 -010
0000 -00x
0000 0000
POR, BOR
2002 Microchip Technology Inc.
Value on
N/A
OSC
/(16(X+1))
0000 -010
0000 -00x
0000 0000
All Other
Value on
RESETS