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SERIAL I/O
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 31
When setting "n" into BRGi (n = "00
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.
F
n =
— 1
16
B
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 30
the BRG count source select bits (bits 0 and 1 at addresses 34
When an external clock is selected, the clock input to the CLK
Tables 7.4.3 to 7.4.5 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)
Transfer
Clock source for peripheral devices select bit = "1"
BRGi count
rate (bps)
source
150
f
64
f
300
64
f
600
16
f
1200
16
f
2400
16
4800
f
2
f
9600
2
f
19200
2
f
31250
2
Clock source for peripheral devices select bit : bit 2 at address 5F
7–36
" to "FF
"), BRGi divides the count source frequency by n + 1. The
16
16
n: Value set into BRGi (00
F: BRGi's count source frequency
B: Transfer rate (bps)
, 38
). When an internal clock is selected, the clock selected with
16
16
BRGi setting
Actual time
value : n
(bps)
162 (A2
)
149.78
16
80 (50
)
301.41
16
162 (A2
)
599.12
16
80 (50
)
1205.63
16
40 (28
)
2381.86
16
162 (A2
)
4792.94
16
80 (50
)
9645.06
16
40 (28
)
19054.88
16
24 (18
)
31250.00
16
7751 Group User's Manual
, 39
).
16
16
16
, 3C
) becomes the BRGi's count source.
16
16
pin becomes the BRGi's count source.
i
f(X
) = 25 MHz
IN
Clock source for peripheral devices select bit = "0"
BRGi count
source
f
128
f
32
f
32
f
32
f
4
f
4
f
4
16
to FF
)
16
BRGi setting
Actual time
value : n
(bps)
80 (50
)
150.70
16
162 (A2
)
299.56
16
80 (50
)
602.82
16
40 (28
)
1190.93
16
162 (A2
)
2396.47
16
80 (50
)
4822.53
16
40 (28
)
9527.44
16
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