UARTs LH79524/LH79525 User’s Guide
16-14 Version 1.0
16.3.2.6 Fractional Baud Rate Divisor Register (UARTFBRD)
UARTFBRD is the fractional portion of the baud rate divisor value.
16.3.2.6.1 Calculating the Divisor Value
The following example shows how to program a divisor value. This example assumes that
the required baud rate is 460,800 and the UARTCLK = 11.2896 MHz.
1. Baud Rate Divisor = (11.2896 × 10
6
) ÷ (16 × 460,800) = 1.53125
2. Integer part, i = integer (1.53125) = 1
3. Fractional part, m = integer ((0.53125 × 64) + 0.5) = 34
4. Generated baud rate divider = 1 + 34/64 = 1.53125
5. Generated baud rate = (11.2896 × 10
6
) ÷ (16 × 1.53125) = 460,800
The maximum error using a 6-bit UARTFBRD Register = 1/64 × 100 = 1.56%. This occurs
when m = 1 and the error is cumulative over 64 clock ticks. Using an 11.2896 MHz crystal
produces the standard baud rates with no error.
16.3.2.6.2 Typical Baud Rates and Their Corresponding Divisor
Table 16-18 shows typical baud rates and their corresponding divisor using an example
UART clock frequency of 11.2896 MHz.
Table 16-16. UARTFBRD Register
BIT 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
FIELD ///
RESET 0000000000000000
RW RO RO RO RO RO RO RO RO RO RO RO RO RO RO RO RO
BIT 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
FIELD /// FRAC
RESET 0000000000000000
RW RO RO RO RO RO RO RO RO RO RO RW RW RW RW RW RW
ADDR
UART 0: 0xFFFC0000 + 0x028
UART 1: 0xFFFC1000 + 0x028
UART 2: 0xFFFC2000 + 0x028
Table 16-17. UARTFBRD Fields
BIT NAME DESCRIPTION
31:6 /// Reserved Reading returns 0. Write the reset value.
5:0 FRAC
Fractional Baud Rate Divisor This value is used with the Integer Baud Rate Divisor to
program the baud rate for the UART. See Section 16.3.2.6.1 and Section 16.3.2.5.
Table 16-18. Bit Rates and Their Corresponding Divisors
UART CLK (MHz) BAUD RATE
INTEGER DIVISOR
(UARTIBRD)
FRACTIONAL DIVISOR, m
(UARTFBRD)
11.2896 921,600 0 49
11.2896 460,800 1 34
11.2896 230,400 3 4
11.2896 115,200 6 8
11.2896 76,800 9 12
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