Datasheet

Table Of Contents
PIC16(L)F1526/7
DS41458C-page 268 2011-2013 Microchip Technology Inc.
22.4 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 BAUDxCON register selects 16-bit
mode.
The SPxBRGH:SPxBRGL 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
TXxSTA register and the BRG16 bit of the BAUDxCON
register. In Synchronous mode, the BRGH bit is ignored.
Example 22-1 provides a sample calculation for deter-
mining the desired baud rate, actual 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 22-5. 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 SPxBRGH, SPxBRGL
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 22-1: CALCULATING BAUD
RATE ERROR
For a device with FOSC of 16 MHz, desired baud rate
of 9600, Asynchronous mode, 8-bit BRG:
Solving for SPxBRGH:SPxBRGL:
SPxBRGH: SPxBRGL
F
OSC
Desired Baud Rate
---------------------------------------------
64
--------------------------------------------- 1=
Desired Baud Rate
F
OSC
64 [SPxBRGH:SPxBRG] 1+
--------------------------------------------------------------------------=
16000000
9600
------------------------
64
------------------------1=
25.04225==
ActualBaudRate
16000000
64 25 1+
---------------------------=
9615=
Calc. Baud Rate Desired Baud Rate
Desired Baud Rate
--------------------------------------------------------------------------------------------
9615 9600
9600
---------------------------------- 0 . 1 6 %==
Baud Rate % Error =
TABLE 22-3: BAUD RATE FORMULAS
Configuration Bits
BRG/EUSART Mode
Baud Rate Formula
SYNC BRG16 BRGH
000 8-bit/Asynchronous FOSC/[64 (n+1)]
001 8-bit/Asynchronous
F
OSC/[16 (n+1)]
010 16-bit/Asynchronous
011 16-bit/Asynchronous
F
OSC/[4 (n+1)]10x 8-bit/Synchronous
11x 16-bit/Synchronous
Legend: x = Don’t care, n = value of SPxBRGH, SPxBRGL register pair