NEC mPD780851, Preliminary User'S Manual

Page: 179 / 315

179
CHAPTER 13 SERIAL INTERFACE UART
Preliminary User’s Manual U14581EJ3V0UM00
The transmit/receive clock that is used to generate the baud rate is obtained by dividing the main system
clock.
• Use of main system clock to generate a transmit/receive clock for baud rate
The main system clock is divided to generate the transmit/receive clock. The baud rate generated by
the main system clock is determined according to the following formula.
[Baud rate] =
f
X
[Hz]
2
n + 1
(k + 16)
f
X
: Main system clock oscillation frequency
n: Value set via TPS0 to TPS2 (1
≤
n
≤
8)
For details, see Table 13-2.
k: Value set via MDL0 to MDL3 (0
≤
k
≤
14)
Table 13-2 shows the relation between the 5-bit counter’s source clock assigned to bits 4 to 6 (TPS0 to TPS2)
of BRGC and the “n” value in the above formula.
Table 13-2. Relation between 5-Bit Counter’s Source Clock and “n” Value
TPS2 TPS1 TPS0 5-bit Counter’s Source Clock Selection n
0 0 0 f
X
/2 1
0 0 1 f
X
/2
2
2
0 1 0 f
X
/2
3
3
0 1 1 f
X
/2
4
4
1 0 0 f
X
/2
5
5
1 0 1 f
X
/2
6
6
1 1 0 f
X
/2
7
7
1 1 1 f
X
/2
8
8
Remark f
X
: Main system clock oscillation frequency (f
X
= 8.38 MHz)