BLUENRG-1 datasheet(63/173 Pages) STMICROELECTRONICS

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BlueNRG-1

Functional details

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The maximum deviation error using a 6-bit UART_FBRD register is 1/64 * 100 = 1.56%.

This occurs when DIVFRAC = 1, and the error is cumulative over 64 clock ticks.

Example 1: Calculating the divisor value (with OVSFACT = 0b).

If the required baud rate is 460 800 and the UART clock frequency is 16 MHz then:

Baud rate divisor = (16 x 106) / (16 x 460 800) = 2.170

BRDI = 2 and BRDF = 0.170

Therefore fractional part DIVFRAC = integer(BRDF * 64 + 0.5) = 11

Generated baud rate divider = 2 + (11 / 64) = 2.1718

Generated baud rate = (16 x 106) / (16 x 2.172) = 460 447

Error = (460 800 - 460 405) / 460 800 x 100 = 0.077 %

An internal clock enable signal, Baudl6, is generated, and is a stream of one UARTCLK

wide pulses with an average frequency of 16 (OVSFACT = 0b) or 8 (OVSFACT = 1b) times

the desired baud rate. This signal is then divided by 16 or 8 to give the transmit clock. A

low number in the baud rate divisor gives a short bit period, and a high number in the baud

rate divisor gives a long bit period.

Table 65: "Typical baud rates with OVSFACT = 0" shows some typical bit rates and their

corresponding divisors when OVSFACT = 0b, given the UART clock frequency of 16 MHz.

Table 65: Typical baud rates with OVSFACT = 0

Required bit rate

(bps)

Programmed divisor

Generated bit rate

(bps)

Error

(%)

Integer

(DIVINT)

Fraction

(DIVFRAC)

921 600

1 (16’h0001)

5 (6’h05)

927 557

0.646

460 800

2 (16’h0002)

11 (6’h0B)

460 447

- 0.077

230 400

4 (16’h0004)

2 (6’h16)

230 218

- 0.079

115 200

8 (16’h0008)

44 (6’h2C)

115 107

- 0.081

57 600

17 (16’h0011)

23 (6’h17)

57 606

0.010

38 400

26 (16’h001A)

3 (6’h03)

38 392

- 0.021

28 800

34 (16’h0022)

46 (6’h2E)

28 802

0.007

19 200

52 (16’h0034)

5 (6’h05)

19 201

0.005

9 600

104 (16’h0068)

11 (6’h0B)

9 599

- 0.010

2 400

416 (16’h01A0)

43 (6’h2B)

2 399

- 0.042

1 200

833 (16’h04B0)

21 (6’h15)

1 200

300

3333

(16’h0D05)

21 (6’h15)

300

110

9090

(16’h2382)

58 (6’h3A)

110

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