12.4.5 Baud Rate Registers (DLR, DMR, and DFR)

Table 12-8. DLR
Bit Number	Name	R/W	Reset Value	Description
[7:0]	DLR	R/W	0x01	This divisor latch LSB register (Table 12-8) holds the LSB of the integer divisor value used to calculate the baud rate. The baud rate can be calculated using EQ 1, 2, 3, or 4.

Table 12-9. DMR
Bit Number	Name	R/W	Reset Value	Description
[7:0]	DMR	R/W	0x00	This divisor latch MSB register (Table 12-9) holds the MSB of the integer divisor value used to calculate the baud rate. The baud rate can be calculated using EQ 1, 2, 3, or 4.

Table 12-10. DFR
Bit Number	Name	R/W	Reset Value	Description
[5:0]	DFR	R/W	0x00	The fractional divisor register (Table 12-10) is used to store the fractional divisor used to calculate the fractional baud rate value in 1/64^th. 0x0: 0/64 0x1: 1/64 …. 0x3F: 63/64

As explained earlier, the divisor value has an integer part and a fractional part. Calculate the 6-bit number (k) which is the fractional divisor in Table 12-10 register by taking the fractional part of the required baud rate divisor and multiplying it by 64 (that is, 2ⁿ, where n is the fractional part which is 6) and adding 0.5 to account for rounding errors:

k = integer (fractional part of divisor value × 2ⁿ + 0.5)

For example, to generate the baud rate of 134.5 the reference clock is 18.432 MHz.

FAPBCLK = 18.432 MHz, Fractional BR = 134.5, Hence, calculate the divisor value = (18.432 × 10⁶) / (16 × 134.5) = 8,565.05

The integer part of divisor = 8565 and fractional part of divisor = 0.05

Therefore, the fractional part, k = integer ((0.05 × 64) + 0.5) = 3.7 ~ = 4

The following table contains the list of baud rates and corresponding values of DFR and DMR+DLR registers.

Table 12-11. Baud Rates and Divisor Values for the 18.432 MHz Reference Clock
Baud Rate	Divisor	DLR + DMR Integer Divisor	DFR Fractional Divisor in 64^th	Percent Error
50	23,040	23,040	0	0.00000%
75	15,360	15,360	0	0.00000%
110	10,472.72	10,472	47	0.00007%
134.5	8,565.05	8,565	4	0.00008%
150	7,680	7,680	0	0.00000%
2,000	576	576	0	0.00000%
38,400	30	30	0	0.00000%
56,000	21.57	21	37	0.03255%