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SERIAL I/O

7721 Group User’s Manual

11–32

11.4 Clock asynchronous serial I/O (UART) mode

11.4.1 Transfer rate (Frequency of transfer clock)

The transfer rate is determined by the BRGi (addresses 3116, 3916).

When setting “n” into BRGi, BRGi divides the count source frequency by (n + 1). The BRGi’s output is

further divided by 16, and the resultant clock becomes the transfer clock. Accordingly, “n” is expressed by

the following formula.

n =

— 1

16 ! B

n: Value set in BRGi (0016 to FF16)

F: BRGi’s count source frequency (Hz)

B: Transfer rate (bps)

An internal clock or an external clock can be selected as the BRGi’s count source with the internal/external

clock select bit (bit 3 at addresses 3016, 3816). When an internal clock is selected, the clock selected with

the BRG count source select bits (bits 0 and 1 at addresses 3416, 3C16) becomes the BRGi’s count source.

When an external clock is selected, the clock input to the CLKi pin becomes the BRGi’s count source.

Set the same transfer rate for both transmitter and receiver sides. Tables 11.4.3 and 11.4.4 list the setting

examples of transfer rate.

Table 11.4.3 Setting examples of transfer rate (1)

BRGi’s set

value : n

79 (4F16)

159 (9F16)

79 (4F16)

39 (2716)

159 (9F16)

79 (4F16)

52 (3416)

39 (2716)

19 (1316)

Actual time

(bps)

300.00

600.00

1200.00

2400.00

4800.00

9600.00

14490.57

19200.00

38400.00

BRGi’s

count source

f64

f16

BRGi’s set

value : n

80 (5016)

162 (A216)

80 (5016)

40 (2816)

162 (A216)

80 (5016)

53 (3516)

40 (2816)

24 (1816)

Actual time

(bps)

301.41

599.12

1205.63

2381.86

4792.94

9645.06

14467.59

19054.58

31250.00

BRGi’s

count source

f64

f16

f(XIN) = 25 MHz

f(XIN) = 24.576 MHz

Transfer

rate (bps)

300

600

1200

2400

4800

9600

14400

19200

31250

38400

BRGi’s set

value : n

71 (4716)

143 (8F16)

71 (4716)

35 (2316)

143 (8F16)

71 (4716)

47 (2F16)

35 (2316)

23 (1716)

21 (1516)

17 (1116)

11 (0B16)

5 (0516)

2 (0216)

Actual time

(bps)

300.00

600.00

1200.00

2400.00

4800.00

9600.00

14400.00

19200.00

28800.00

31418.18

38400.00

57600.00

115200.00

230400.00

BRGi’s

count source

f64

f16

f(XIN) = 22.1184 MHz

Transfer

rate (bps)

300

600

1200

2400

4800

9600

14400

19200

28800

31250

38400

57600

115200

230400

Table 11.4.4 Setting examples of transfer rate (2)

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