PIC18F44J50-I Datasheet, PDF (327/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
20.1 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, bits,
BRGH (TXSTAx<2>) and BRG16 (BAUDCONx<3>),
also control the baud rate. In Synchronous mode, BRGH
is ignored.
Table 20-1 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 20-1. From
this, the error in baud rate can be determined. An
example calculation is provided in Example 20-1.
Typical baud rates and error values for the various
Asynchronous modes are provided in Table 20-2. 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.
When operated in the Synchronous mode,
SPBRGH:SPBRG values of 0000h and 0001h are not
supported. In the Asynchronous mode, all BRG values
may be used.
20.1.1
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.
20.1.2 SAMPLING
The data on the RXx pin (either
RC7/PMA4/RX1/DT1/SDO1/RP18 or RPn/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 20-1: 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)]
 2011 Microchip Technology Inc.
DS39931D-page 327