NEC UPD789026 Series User Manual page 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] =
f : System clock oscillation frequency
X
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
Baud Rate (bps)
1,200
2,400
4,800
9,600
19,200
38,400
76,800
Caution Be sure not to select n = 1 during an operation at f
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130
CHAPTER 9 SERIAL INTERFACE 00
f
X
[Hz]
× 8
n + 1
2
n BRGC00 Set Value
8
7
6
5
4
3
2
the baud rate limit.
User's Manual U11919EJ3V0UM00
f = 5.0 MHz
X
70H 1.73
60H
50H
40H
30H
20H
10H
Error (%)
f = 4.9152 MHz
X
0
= 5.0 MHz because n = 1 exceeds
X