NEC PD789488 User Manual page 196

(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] =
f : Frequency of clock input to the ASCK20 pin
ASCK
Table 11-4. Relationship Between ASCK20 Pin Input Frequency
(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 =
f : Main system clock oscillation frequency
X
n: Values in Figure 11-6 determined by the settings of TPS200 to TPS203 (1 ≤ n ≤ 8)
196
CHAPTER 11 SERIAL INTERFACE 20
f
ASCK
[bps]
16
and Baud Rate (When BRGC20 Is Set to 80H)
Baud Rate (bps)
75
150
300
600
1,200
2,400
4,800
9,600
19,200
31,250
38,400
f
X
[Hz]
n+1
2
User's Manual U15331EJ4V1UD
ASCK20 Pin Input Frequency (kHz)
1.2
2.4
4.8
9.6
19.2
38.4
76.8
153.6
307.2
500.0
614.4