PIC24FJ64GA006-I Datasheet, PDF (146/258 Pages) Microchip Technology – 64/80/100-Pin, General Purpose, 16-Bit Flash Microcontrollers

PIC24FJ128GA010 FAMILY
17.1 UARTx Baud Rate Generator
(BRG)
The UARTx module includes a dedicated, 16-bit Baud
Rate Generator. The UBRGx register controls the
period of a free-running, 16-bit timer. Equation 17-1
shows the formula for computation of the baud rate
with BRGH = 0.
EQUATION 17-1: UARTx BAUD RATE WITH
BRGH = 0⁽¹⁾
Baud Rate =
FCY
16 • (UBRGx + 1)
UBRGx =
FCY
–1
16 • Baud Rate
The maximum baud rate (BRGH = 0) possible is
FCY/16 (for UBRGx = 0) and the minimum baud rate
possible is FCY/(16 * 65536).
Equation 17-2 shows the formula for computation of
the baud rate with BRGH = 1.
EQUATION 17-2: UARTx BAUD RATE WITH
BRGH = 1⁽¹⁾
Baud Rate =
FCY
4 • (UBRGx + 1)
UBRGx =
FCY
–1
4 • Baud Rate
Note 1: Based on FCY = FOSC/2; Doze mode
and PLL are disabled.
Note 1: Based on FCY = FOSC/2; Doze mode
and PLL are disabled.
Example 17-1 shows the calculation of the baud rate
error for the following conditions:
• FCY = 4 MHz
• Desired Baud Rate = 9600
The maximum baud rate (BRGH = 1) possible is FCY/4
(for UBRGx = 0) and the minimum baud rate possible
is FCY/(4 * 65536).
Writing a new value to the UBRGx register causes the
BRG timer to be reset (cleared). This ensures the BRG
does not wait for a timer overflow before generating the
new baud rate.
EXAMPLE 17-1: BAUD RATE ERROR CALCULATION (BRGH = 0)⁽¹⁾
Desired Baud Rate = FCY/(16 (UBRGx + 1))
Solving for UBRGx value:
BRGx
BRGx
BRGx
= ((FCY/Desired Baud Rate)/16) – 1
= ((4000000/9600)/16) – 1
= 25
Calculated Baud Rate = 4000000/(16 (25 + 1))
= 9615
Error
= (Calculated Baud Rate – Desired Baud Rate)
Desired Baud Rate
= (9615 – 9600)/9600
= 0.16%
Note 1: Based on FCY = FOSC/2; Doze mode and PLL are disabled.
DS39747F-page 146
 2005-2012 Microchip Technology Inc.