Datasheet

j
i
i=0
baud rate
Error [%] = × (j + 1) × UxBR + m – (j + 1) × 100%
BRCLK
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www.ti.com USART Operation: UART Mode
18.2.6.2 Determining the Modulation Value
Determining the modulation value is an interactive process. Using the timing error formula provided,
beginning with the start bit , the individual bit errors are calculated with the corresponding modulator bit set
and cleared. The modulation bit setting with the lower error is selected and the next bit error is calculated.
This process is continued until all bit errors are minimized. When a character contains more than 8 bits,
the modulation bits repeat. For example, the ninth bit of a character uses modulation bit 0.
18.2.6.3 Transmit Bit Timing
The timing for each character is the sum of the individual bit timings. By modulating each bit, the
cumulative bit error is reduced. The individual bit error can be calculated by:
Where,
baud rate = Desired baud rate
BRCLK = Input frequency - UCLKI, ACLK, or SMCLK
j = Bit position - 0 for the start bit, 1 for data bit D0, and so on
UxBR = Division factor in registers UxBR1 and UxBR0
For example, the transmit errors for the following conditions are calculated:
Baud rate = 2400
BRCLK = 32 768 Hz (ACLK)
UxBR = 13, since the ideal division factor is 13.65
UxMCTL = 6Bh: m7 = 0, m6 = 1, m5 = 1, m4 = 0, m3 = 1, m2 = 0, m1 = 1, and m0 = 1. The LSB of
UxMCTL is used first.
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SLAU144J–December 2004–Revised July 2013 USART Peripheral Interface, UART Mode
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