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SERIAL I/O
7702/7703 Group User’s Manual
7–36
7.4 Clock asynchronous serial I/O (UART) mode
7.4.1 Transfer rate (frequency of transfer clock)
The transfer rate is determined by the BRGi (addresses 3116, 3916).
When setting “n” into BRGi (n = “0016” to “FF16”), BRGi divides the count source frequency by n + 1. The
divided clock by BRGi is further divided by 16 and the resultant clock becomes the transfer clock. Accordingly,
the value “n” is expressed by the following formula.
n =
— 1
F
16 ! B
n: Value set into BRGi
F: BRGi’s count source frequency
B: Transfer rate
Transfer
rate (bps)
75
110
134.5
150
300
600
1200
2400
4800
9600
19200
31250
62500
125000
250000
500000
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.
Tables 7.4.3 and 7.4.4 are list the setting examples of transfer rate. Set the same transfer rate between
the transmitter and the receiver.
Table 7.4.3 Setting examples of transfer rate (1)
BRGi setting
value : n
12 (0C16)
70 (4616)
57 (3916)
51 (3316)
25 (1916)
12 (0C16)
25 (1916)
12 (0C16)
51 (3316)
25 (1916)
12 (0C16)
7 (0716)
3 (0316)
1 (0116)
0 (0016)
Actual time
(bps)
75.12
110.04
134.70
150.24
300.48
600.96
1201.92
2403.85
4807.69
9615.39
19230.77
31250.00
62500.00
125000.00
250000.00
BRGi count
source
f512
f64
f16
f2
BRGi setting
value : n
25 (1916)
141 (8D16)
115 (7316)
103 (6716)
51 (3316)
25 (1916)
51 (3316)
25 (1916)
103 (6716)
51 (3316)
25 (1916)
15 (0F16)
7 (0716)
3 (0316)
1 (0116)
0 (0016)
Actual time
(bps)
75.12
110.04
134.70
150.24
300.48
600.96
1201.92
2403.85
4807.69
9615.39
19230.77
31250.00
62500.00
125000.00
250000.00
500000.00
BRGi count
source
f512
f64
f16
f2
f(XIN) = 8 MHz
f(XIN) = 16 MHz