PIC16LF18854 Datasheet, PDF (563/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
33.3 EUSART Baud Rate Generator
(BRG)
The Baud Rate Generator (BRG) is an 8-bit or 16-bit
timer that is dedicated to the support of both the
asynchronous and synchronous EUSART operation.
By default, the BRG operates in 8-bit mode. Setting the
BRG16 bit of the BAUD1CON register selects 16-bit
mode.
The SPBRGH, SPBRGL register pair determines the
period of the free running baud rate timer. In
Asynchronous mode the multiplier of the baud rate
period is determined by both the BRGH bit of the
TX1STA register and the BRG16 bit of the BAUD1CON
register. In Synchronous mode, the BRGH bit is ignored.
Table 33-1 contains the formulas for determining the
baud rate. Example 33-1 provides a sample calculation
for determining the baud rate and baud rate error.
Typical baud rates and error values for various
Asynchronous modes have been computed for your
convenience and are shown in Table 33-3. It may be
advantageous to use the high baud rate (BRGH = 1),
or the 16-bit BRG (BRG16 = 1) to reduce the baud rate
error. The 16-bit BRG mode is used to achieve slow
baud rates for fast oscillator frequencies.
Writing a new value to the SPBRGH, SPBRGL register
pair causes the BRG timer to be reset (or cleared). This
ensures that the BRG does not wait for a timer overflow
before outputting the new baud rate.
If the system clock is changed during an active receive
operation, a receive error or data loss may result. To
avoid this problem, check the status of the RCIDL bit to
make sure that the receive operation is idle before
changing the system clock.
EXAMPLE 33-1: 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 = _{6---4----}--[---S---P---B----R----G----FH----^O_:--S--^S-P-^C---B----R---G-----L---]----+-----1----_
Solving for SPBRGH:SPBRGL:
----------------F----^O----^S---^C------------------
X = -D----e---s--i--r--e---d----B----a---u---d----R----a---t--e- – 1
64
1---6---0----0--0---0---0---0--
= ------9----6---0--0-------- – 1
64
= 25.042 = 25
Calculated Baud Rate = _{6--1-4--6--}-0-2--0-5--0---+0---0--1-0---_
= 9615
Error = ^{C-----a---l-c---.---B----a---u-D--d---e-R-s---ia-r--t-ee--d---–}--B--D-a---eu---sd--i--r-R-e---ad---t-e-B---a---u---d-----R---a---t--e---
= ^---9---6---1---5----^–-----9---6---0---0---^- = 0.16%
9600
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Preliminary
DS40001824A-page 563