NEC PD789488, Руководство пользователя

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CHAPTER 11 SERIAL INTERFACE 20
196
User’s Manual U15331EJ4V1UD
(b) Generation of UART baud rate transmit/receive clock from external clock input to ASCK20 pin
The transmit/receive clock is generated by dividing the clock input from the ASCK20 pin. The baud rate
of a clock generated from the clock input to the ASCK20 pin is estimated by using the following
expression.
[Baud rate] = [bps]
f
ASCK
: Frequency of clock input to the ASCK20 pin
Table 11-4. Relationship Between ASCK20 Pin Input Frequency
and Baud Rate (When BRGC20 Is Set to 80H)
Baud Rate (bps) ASCK20 Pin Input Frequency (kHz)
75 1.2
150 2.4
300 4.8
600 9.6
1,200 19.2
2,400 38.4
4,800 76.8
9,600 153.6
19,200 307.2
31,250 500.0
38,400 614.4
(c) Generation of serial clock from system clock in 3-wire serial I/O
The serial clock is generated by dividing the system clock. The frequency of the serial clock can be
obtained by the following expression. If the serial clock is externally input to the SCK20 pin, it is
unnecessary to set BRGC20.
Serial clock frequency = [Hz]
f
X
: Main system clock oscillation frequency
n: Values in Figure 11-6 determined by the settings of TPS200 to TPS203 (1
≤
n
≤
8)
f
ASCK
16
f
X
2
n+1