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: Value set in BRGi (0016 to FF16
F: BRGi’s count source frequency (Hz)
B: Transfer rate (bps)
)
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 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 CLK pin becomes the BRGi’s count source.
i
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)
f
sys = 19.6608 MHz
BRGi’s set
fsys = 20 MHz
Transfer
BRGi’s set
Actual time
(bps)
Actual time
(bps)
BRGi’s
BRGi’s
rate (bps)
value: n (Note)
value: n (Note)
count source
count source
64 (4016
129 (8116
64 (4016
)
)
)
300.48
63 (3F16
127 (7F16
63 (3F16
31 (1F16
127 (7F16
63 (3F16
42 (2A16
31 (1F16
)
)
)
)
)
)
)
)
300.00
f
f
f
64
16
16
300
600
f
f
f
f
f
f
f
f
64
16
16
16
2
600.96
600.00
1201.92
1200.00
2400.00
4800.00
9600.00
14288.37
19200.00
1200
2400
129 (8116
64 (4016
42 (2A16
)
)
)
4807.69
9615.38
f
f
f
2
2
2
4800
9600
2
14534.88
14400
19200
31250
38400
2
2
19 (1316
)
31250.00
f
2
15 (0F16
)
38400.00
f
2
Note: This applies when the peripheral device’s clock select bits 1, 0 (bits 7, 6 at address BC16) = “00 .”
2
Table 11.4.4 Setting examples of transfer rate (2)
f
sys = 15.9744 MHz
BRGi’s set
fsys = 16 MHz
Transfer
BRGi’s set
Actual time
(bps)
Actual time
(bps)
BRGi’s
BRGi’s
rate (bps)
value: n (Note)
value: n (Note)
count source
count source
51 (3316
103 (6716
51 (3316
)
)
)
)
)
)
300.48
51 (3316
103 (6716
51 (3316
207 (CF16
103 (6716
51 (3316
34 (2216
25 (1916
)
)
)
)
)
)
)
)
300.00
f
f
f
f
f
f
64
16
16
2
300
600
f
f
f
f
f
f
f
f
f
f
64
16
16
2
600.96
600.00
1201.92
2403.85
4807.69
9615.38
1200.00
2400.00
4800.00
9600.00
14262.86
19200.00
31200.00
38400.00
1200
207 (CF16
103 (6716
51 (3316
2400
2
4800
2
2
9600
2
14400
19200
31250
38400
2
25 (1916
15 (0F16
12 (0C16
)
)
)
19230.77
31250.00
38461.51
f
f
f
2
2
2
2
15 (0F16
)
2
12 (0C16
)
2
Note: This applies when the peripheral device’s clock select bits 1, 0 (bits 7, 6 at address BC16) = “00 .”
2
7906 Group User’s Manual Rev.2.0
11-37
RENESAS [ RENESAS TECHNOLOGY CORP ]
