PIC24FV16KM204 Datasheet, PDF (174/336 Pages) Microchip Technology – General Purpose, 16-Bit Flash Microcontroller with XLP Technology Data Sheet

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15.1 UARTx Baud Rate Generator
(BRG)
The UARTx module includes a dedicated 16-bit Baud
Rate Generator (BRG). The UxBRG register controls
the period of a free-running, 16-bit timer. Equation 15-1
provides the formula for computation of the baud rate
with BRGH = 0.
EQUATION 15-1: UARTx BAUD RATE WITH
BRGH = 0⁽¹⁾
Baud Rate =
FCY
16 • (UxBRG + 1)
UxBRG =
FCY
16 • Baud Rate
–1
Note 1: Based on FCY = FOSC/2; Doze mode
and PLL are disabled.
Example 15-1 provides the calculation of the baud rate
error for the following conditions:
• FCY = 4 MHz
• Desired Baud Rate = 9600
The maximum baud rate (BRGH = 0) possible is
FCY/16 (for UxBRG = 0) and the minimum baud rate
possible is FCY/(16 * 65536).
Equation 15-2 shows the formula for computation of
the baud rate with BRGH = 1.
EQUATION 15-2: UARTx BAUD RATE WITH
BRGH = 1⁽¹⁾
Baud Rate =
FCY
4 • (UxBRG + 1)
UxBRG =
FCY
4 • Baud Rate
–1
Note 1: Based on FCY = FOSC/2; Doze mode
and PLL are disabled.
The maximum baud rate (BRGH = 1) possible is FCY/4
(for UxBRG = 0) and the minimum baud rate possible
is FCY/(4 * 65536).
Writing a new value to the UxBRG 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 15-1: BAUD RATE ERROR CALCULATION (BRGH = 0)⁽¹⁾
Desired Baud Rate = FCY/(16 (UxBRG + 1))
Solving for UxBRG value:
UxBRG
UxBRG
UxBRG
= ((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.
DS33030A-page 174
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 2013 Microchip Technology Inc.