NEC mPD789101, User Manual

Page: 171 / 265

CHAPTER 13 SERIAL INTERFACE 20
User’s Manual U13045EJ2V0UM00
171
(4) Baud rate generator control register 20 (BRGC20)
BRGC20 is used to specify the serial clock for serial interface.
BRGC20 is set with an 8-bit memory manipulation instruction.
RESET input clears BRGC20 to 00H.
Figure 13-6. Baud Rate Generator Control Register 20 Format
Note An external clock can only be used in UART mode.
Cautions 1. When writing to BRGC20 is performed during a communication operation, the output of
baud rate generator is disrupted and communications cannot be performed normally. Be
sure not to write to BRGC20 during communication operations.
2. Be sure not to select n = 1 during operation at f
X
= 5.0 MHz because n = 1 exceeds the
baud rate limit.
3. When the external input clock is selected, set port mode register 2 (PM2) in input mode.
Remarks 1. f
X
: System clock oscillation frequency (ceramic/crystal oscillation)
2. n: Value specified in TPS200 to TPS203 (1
≤
n
≤
8)
3. Values in parentheses apply to operation with f
X
= 5.0 MHz.
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 pulse input at 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
–