Serial Interface 20 Operation; Operation Stop Mode - NEC mPD789101 User Manual

13.4 Serial Interface 20 Operation

Serial interface 20 provides the following three types of modes.

• Operation stop mode

• Asynchronous serial interface (UART) mode
• 3-wire serial I/O mode
13.4.1 Operation stop mode
In the operation stop mode, serial transfer is not executed, therefore, the power consumption can be reduced. The
P20/SCK20/ASCK20, P21/SO20/TxD20, and P22/SI20/RxD20 pins can be used as normal I/O ports.
(1) Register setting
Operation stop mode is set by serial operating 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
CSIM20 CSIE20 SSE20
CSIE20
0 Operation disable
1
Operation enable
Caution Be sure to set bits 4 and 5 to 0.
174
CHAPTER 13 SERIAL INTERFACE 20
5 4 3 2 1
0 0 DAP20 DIR20 CSCK20 CKP20
Operation control in 3-wire serial I/O mode
User's Manual U13045EJ2V0UM00
0 Address After reset
FF72H 00H
R/W
R/W