Calculating The Divisor Value; Typical Bit Rates And Their Corresponding Divisor; Table 19-15. Bit Rates And Their Corresponding Divisors - Sharp Blue Treak LH75400 User Manual

UART0 and UART1

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
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. 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.
19-14

Table 19-15. Bit Rates and Their Corresponding Divisors

UART CLK
BAUD RATE
(MHz)
14.7456 921600
14.7456 460800
14.7456 230400
14.7456 153600
14.7456 115200
14.7456 76800
LH75400/01/10/11 (Preliminary) User's Guide
6
) ÷ (16 × 230,400) = 1.085
6
) ÷ (16 × 1.078) = 231,911
INTEGER DIVISOR
(IBRD)
1
2
4
6
8
12
7/15/03
FRACTIONAL DIVISOR
(FBRD)
0
0
0
0
0
0