NEC UPD789026 Series, User Manual

Page: 130 / 213

CHAPTER 9 SERIAL INTERFACE 00
User's Manual U11919EJ3V0UM00
130
The baud rate transmit/receive clock to be generated is either a signal scaled from the system clock, or a
signal scaled from the clock input from the ASCK pin.
(a) Generation of baud rate transmit/receive clock by means of system clock
The transmit/receive clock is generated by scaling the system clock. The baud rate generated from the
system clock is found from the following expression.
[Baud rate] = [Hz]
f
X
: System clock oscillation frequency
n : Value determined by values of TPS000 through TPS003 as shown in Figure 9-6 (2
≤
n
≤
8)
Table 9-3. Example of Relationship between System Clock and Baud Rate
Error (%) Baud Rate (bps) n BRGC00 Set Value
f
X
= 5.0 MHz f
X
= 4.9152 MHz
1,200 8 70H
2,400 7 60H
4,800 6 50H
9,600 5 40H
19,200 4 30H
38,400 3 20H
76,800 2 10H
1.73 0
Caution Be sure not to select n = 1 during an operation at f
X
= 5.0 MHz because n = 1 exceeds
the baud rate limit.
f
X
2
n + 1
×
8
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