NEC mPD789425, User Manual

Page: 219 / 321

CHAPTER 12 SERIAL INTERFACE 20
User’s Manual U15075EJ1V0UM00
219
(4) Baud rate generator control register 20 (BRGC20)
BRGC20 is used to specify the serial clock for serial interface 20.
BRGC20 is set with an 8-bit memory manipulation instruction.
RESET input sets BRGC20 to 00H.
Figure 12-6. Format of Baud Rate Generator Control Register 20
TPS203
0
0
0
0
0
0
0
0
1
3-bit counter source clock selection
TPS203 TPS202 TPS201 TPS200 0 0 0 0 BRGC20
Symbol Address After reset R/W
FF73H 00H R/W
7 6 5 4 3 2 1 0
TPS202
0
0
0
0
1
1
1
1
0
f
X
/2
f
X
/2
2
f
X
/2
3
f
X
/2
4
f
X
/2
5
f
X
/2
6
f
X
/2
7
f
X
/2
8
External clock input to the ASCK20 pin
Note
Setting prohibited
(2.5 MHz)
(1.25 MHz)
(625 kHz)
(313 kHz)
(156 kHz)
(78.1 kHz)
(39.1 kHz)
(19.5 kHz)
Other than above
TPS201
0
0
1
1
0
0
1
1
0
TPS200
0
1
0
1
0
1
0
1
0
n
1
2
3
4
5
6
7
8
−
Note An external clock can be used only in UART mode.
Cautions 1. When writing to BRGC00 during a communication operation, the output of the baud
rate generator is disrupted and communications cannot be performed normally. Be
sure not to write to BRGC00 during a communication operation.
2. Be sure not to select n = 1 during operation at f
X
= 5.0 MHz because the resulting baud
rate exceeds the rated range.
3. When the external input clock is selected, set port mode register 2 (PM2) to input
mode.
Remarks 1. f
X
: Main system clock oscillation frequency
2. n: Values determined by the settings of TPS200 to TPS203 (1
≤
n
≤
8)
3. The parenthesized values apply to operation at f
X
= 5.0 MHz.