INTEDG datasheet(310/478 Pages) MICROCHIP

310 / 478 page

PIC16(L)F1946/47

DS41414D-page 310

 2010-2012 Microchip Technology Inc.

25.4

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

Example 25-1 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 25-5. 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

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 25-1:

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

FOSC

Desired Baud Rate

---------------------------------------------

--------------------------------------------- 1

–

Desired Baud Rate

FOSC

64 [SPxBRGH:SPxBRG]



--------------------------------------------------------------------------

16000000

9600

------------------------

------------------------1

–

25.042



ActualBaudRate

16000000

64 25



---------------------------

9615

Calc. Baud Rate Desired Baud Rate

–

Desired Baud Rate

--------------------------------------------------------------------------------------------

9615 9600

–



9600

----------------------------------

0.16%

Baud Rate % Error =

TABLE 25-3:

BAUD RATE FORMULAS

Configuration Bits

BRG/EUSART Mode

Baud Rate Formula

SYNC

BRG16

BRGH

8-bit/Asynchronous

FOSC/[64 (n+1)]

8-bit/Asynchronous

FOSC/[16 (n+1)]

16-bit/Asynchronous

FOSC/[4 (n+1)]

8-bit/Synchronous

16-bit/Synchronous

Legend:

x = Don’t care, n = value of SPxBRGH, SPxBRGL register pair

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