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UART0 and UART1
LH75400/01/10/11 (Preliminary) User’s Guide
19-14
7/15/03
19.3.1.7 Calculating the Divisor Value
The following example shows how to clear a divisor value. This example assumes that the
required baud rate is 230,400 and the UARTCLK = 4 MHz.
1.
Baud Rate Divisor = (4 × 10
6
) ÷ (16 × 230,400) = 1.085
2.
BRDt and BRDf = 0.085
3.
Fractional part, m = integer ((0.085 × 64) + 0.5) = 5
4.
Generated baud rate divider = 1 + 5/64 = 1.078
5.
Generated baud rate = (4 × 10
6
) ÷ (16 × 1.078) = 231,911
6.
Error = ((231,911 – 230,400) ÷ 230,400) × 100 = 0.656%
The maximum error using a 6-bit FBRD Register = 1/64 × 100 = 1.56%. This occurs when
m = 1 and the error is cumulative over 64 clock ticks.
19.3.1.8 Typical Bit Rates and Their Corresponding Divisor
Table 19-15 shows some typical bit rates and their corresponding divisor, given the UART
Clock Frequency of 14.7456 MHz.
Table 19-15. Bit Rates and Their Corresponding Divisors
UART CLK
(MHz)
BAUD RATE
INTEGER DIVISOR
(IBRD)
FRACTIONAL DIVISOR
(FBRD)
14.7456
921600
1
0
14.7456
460800
2
0
14.7456
230400
4
0
14.7456
153600
6
0
14.7456
115200
8
0
14.7456
76800
12
0