CHAPTER 12 SERIAL INTERFACE 20
12.4 Serial Interface 20 Operation
Serial interface 20 provides the following three modes.
• Operation stop mode
• Asynchronous serial interface (UART) mode
• 3-wire serial I/O mode
12.4.1 Operation stop mode
In operation stop mode, serial transfer is not executed, thereby reducing the power consumption. The
P23/SCK20/ASCK20, P24/SO20/TxD20, and P25/SI20/RxD20 pins can be used as normal I/O ports.
(1) Register setting
Operation stop mode is set by serial operation mode register 20 (CSIM20) and asynchronous serial
interface mode register 20 (ASIM20).
(a) Serial operation mode register 20 (CSIM20)
CSIM20 is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input clears CSIM20 to 00H.
Symbol
<7>
6
5
0
4
0
3
2
1
0
Address
FF72H
After reset
00H
R/W
R/W
CSIM20 CSIE20 SSE20
DAP20
DIR20
CSCK20 CKP20
CSIE20
Operation control in 3-wire serial I/O mode
0
1
Operation disabled
Operation enabled
Caution Bits 4 and 5 must be set to 0.
User’s Manual U15075EJ1V0UM00
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NEC [ NEC ]
