PIC18F47J53 Datasheet, PDF (349/586 Pages) Microchip Technology – 28/44-Pin, High-Performance USB Microcontrollers with nanoWatt XLP Technology

PIC18F47J53 FAMILY
21.1 Baud Rate Generator (BRG)
The BRG is a dedicated, 8-bit or 16-bit generator that
supports both the Asynchronous and Synchronous
modes of the EUSART. By default, the BRG operates
in 8-bit mode; setting the BRG16 bit (BAUDCONx<3>)
selects 16-bit mode.
The SPBRGHx:SPBRGx register pair controls the period
of a free-running timer. In Asynchronous mode, the
BRGH (TXSTAx<2>) and BRG16 (BAUDCONx<3>) bits
also control the baud rate. In Synchronous mode, BRGH
is ignored.
Table 21-1 provides the formula for computation of the
baud rate for different EUSART modes, which only apply
in Master mode (internally generated clock).
Given the desired baud rate and FOSC, the nearest
integer value for the SPBRGHx:SPBRGx registers can
be calculated using the formulas in Table 21-1. From
this, the error in baud rate can be determined. An
example calculation is provided in Example 21-1.
Typical baud rates and error values for the various
Asynchronous modes are provided in Table 21-2. It
may be advantageous to use the high baud rate
(BRGH = 1) or the 16-bit BRG to reduce the baud rate
error, or achieve a slow baud rate for a fast oscillator
frequency.
Writing a new value to the SPBRGHx:SPBRGx
registers 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.
21.1.1 OPERATION IN POWER-MANAGED
MODES
The device clock is used to generate the desired baud
rate. When one of the power-managed modes is
entered, the new clock source may be operating at a
different frequency. This may require an adjustment to
the value in the SPBRGx register pair.
21.1.2 SAMPLING
The data on the RXx pin (either RC7/CCP10/PMA4/
RX1/DT1/SDO1/RP18 or RPn2/RX2/DT2) is sampled
three times by a majority detect circuit to determine if a
high or a low level is present at the RXx pin.
TABLE 21-1: BAUD RATE FORMULAS
Configuration Bits
SYNC
BRG16
BRGH
BRG/EUSART Mode
0
0
0
0
1
1
Legend:
0
0
8-bit/Asynchronous
0
1
8-bit/Asynchronous
1
0
16-bit/Asynchronous
1
1
16-bit/Asynchronous
0
x
8-bit/Synchronous
1
x
16-bit/Synchronous
x = Don’t care, n = value of SPBRGHx:SPBRGx register pair
Baud Rate Formula
FOSC/[64 (n + 1)]
FOSC/[16 (n + 1)]
FOSC/[4 (n + 1)]
 2010 Microchip Technology Inc.
Preliminary
DS39964B-page 349