NEC U789436 Series, Руководство пользователя

Страница: 223 / 354

CHAPTER 12 SERIAL INTERFACE 20
User’s Manual U15075EJ2V1UD
224
(b) Generation of UART transmit/receive clock for baud rate from external clock input from ASCK20
pin
The transmit/receive clock is generated by scaling 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 12-4. 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 in 3-wire serial I/O mode from system clock
The serial clock is generated by dividing the system clock. The serial clock frequency is estimated by
using the following expression. BRGC20 does not need to be set when an external serial clock is input
to the SCK20 pin.
Serial clock frequency = [Hz]
f
X
: System clock oscillation frequency
n: Value determined by the settings of TPS200 to TPS203 as shown in Figure 12-6 (1
≤
n
≤
8)
f
ASCK
16
f
X
2
n+1