Table 16-16. Uartfbrd Register; Table 16-17. Uartfbrd Fields; Table 16-18. Bit Rates And Their Corresponding Divisors; Fractional Baud Rate Divisor Register (Uartfbrd) - Sharp LH79524 User Manual

UARTs

16.3.2.6 Fractional Baud Rate Divisor Register (UARTFBRD)

UARTFBRD is the fractional portion of the baud rate divisor value.
BIT
FIELD
RESET
RW
BIT
FIELD
RESET
RW
ADDR
BIT NAME
31:6
5:0
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
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
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.
16-14

Table 16-16. UARTFBRD Register

31 30 29 28 27
0 0 0 0
RO RO RO RO RO
15 14 13 12 11
0 0 0 0
RO RO RO RO RO

Table 16-17. UARTFBRD Fields

/// Reserved Reading returns 0. Write the reset value.
Fractional Baud Rate Divisor This value is used with the Integer Baud Rate Divisor to
FRAC
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
11.2896 921,600
11.2896 460,800
11.2896 230,400
11.2896 115,200
11.2896 76,800
26 25 24 23
///
0 0 0 0 0
RO RO RO RO
10 9 8 7
///
0 0 0 0 0
RO RO RO RO
UART 0: 0xFFFC0000 + 0x028
UART 1: 0xFFFC1000 + 0x028
UART 2: 0xFFFC2000 + 0x028
DESCRIPTION
6
) ÷ (16 × 460,800) = 1.53125
6
) ÷ (16 × 1.53125) = 460,800
INTEGER DIVISOR
(UARTIBRD)
0
1
3
6
9
Version 1.0
LH79524/LH79525 User's Guide
22 21 20 19 18
0 0 0 0 0
RO RO RO RO RO
6 5 4 3 2
FRAC
0 0 0 0 0
RO RW RW RW RW
FRACTIONAL DIVISOR, m
(UARTFBRD)
49
34
4
8
12
17 16
0 0
RO RO
1 0
0 0
RW RW