7906 datasheet(278/531 Pages) RENESAS

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7906 Group User’s Manual Rev.2.0

11-37

SERIAL I/O

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 “n” is set 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.

Be sure to 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.

Each of the values, listed in these tables, realizes the actual transfer rate of which error toward an ideal

transfer rate is within 1 %.

Table 11.4.3 Setting examples of transfer rate (1)

Table 11.4.4 Setting examples of transfer rate (2)

Note: This applies when the peripheral device’s clock select bits 1, 0 (bits 7, 6 at address BC16) = “002.”

BRGi’s set

value: n (Note)

63 (3F16)

127 (7F16)

63 (3F16)

31 (1F16)

127 (7F16)

63 (3F16)

42 (2A16)

31 (1F16)

15 (0F16)

Actual time

(bps)

300.00

600.00

1200.00

2400.00

4800.00

9600.00

14288.37

19200.00

38400.00

BRGi’s

count source

f64

f16

BRGi’s set

value: n (Note)

64 (4016)

129 (8116)

64 (4016)

129 (8116)

64 (4016)

42 (2A16)

19 (1316)

Actual time

(bps)

300.48

600.96

1201.92

4807.69

9615.38

14534.88

31250.00

BRGi’s

count source

f64

f16

fsys = 20 MHz

fsys = 19.6608 MHz

Transfer

rate (bps)

300

600

1200

2400

4800

9600

14400

19200

31250

38400

BRGi’s set

value: n (Note)

51 (3316)

103 (6716)

51 (3316)

207 (CF16)

103 (6716)

51 (3316)

34 (2216)

25 (1916)

15 (0F16)

12 (0C16)

Actual time

(bps)

300.00

600.00

1200.00

2400.00

4800.00

9600.00

14262.86

19200.00

31200.00

38400.00

BRGi’s

count source

f64

f16

BRGi’s set

value: n (Note)

51 (3316)

103 (6716)

51 (3316)

207 (CF16)

103 (6716)

51 (3316)

25 (1916)

15 (0F16)

12 (0C16)

Actual time

(bps)

300.48

600.96

1201.92

2403.85

4807.69

9615.38

19230.77

31250.00

38461.51

BRGi’s

count source

f64

f16

fsys = 16 MHz

fsys = 15.9744 MHz

Transfer

rate (bps)

300

600

1200

2400

4800

9600

14400

19200

31250

38400

Note: This applies when the peripheral device’s clock select bits 1, 0 (bits 7, 6 at address BC16) = “002.”

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