Datasheet

CHAPTER 13 SERIAL INTERFACE UART0

User’s Manual U18698EJ1V0UD

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13.4 Operation of Serial Interface UART0

Serial interface UART0 has the following two modes.

• Operation stop mode

• Asynchronous serial interface (UART) mode

13.4.1 Operation stop mode

In this mode, serial communication cannot be executed, thus reducing the power consumption. In addition, the

pins can be used as ordinary port pins in this mode. To set the operation stop mode, clear bits 7, 6, and 5 (POWER0,

TXE0, and RXE0) of ASIM0 to 0.

(1) Register used

The operation stop mode is set by asynchronous serial interface operation mode register 0 (ASIM0).

ASIM0 can be set by a 1-bit or 8-bit memory manipulation instruction.

Reset signal generation sets this register to 01H.

Address: FF70H After reset: 01H R/W

Symbol <7> <6> <5> 4 3 2 1 0

ASIM0 POWER0 TXE0 RXE0 PS01 PS00 CL0 SL0 1

POWER0 Enables/disables operation of internal operation clock

Note 1

Disables operation of the internal operation clock (fixes the clock to low level) and asynchronously

resets the internal circuit

Note 2

TXE0 Enables/disables transmission

0 Disables transmission (synchronously resets the transmission circuit).

RXE0 Enables/disables reception

0 Disables reception (synchronously resets the reception circuit).

Notes 1. The input from the R

XD0 pin is fixed to high level when POWER0 = 0.

2. Asynchronous serial interface reception error status register 0 (ASIS0), transmit shift register 0 (TXS0),

and receive buffer register 0 (RXB0) are reset.

Caution Clear POWER0 to 0 after clearing TXE0 and RXE0 to 0 to set the operation stop mode.

To start the communication, set POWER0 to 1, and then set TXE0 or RXE0 to 1.

Remark To use the RxD0/KR3/<RxD6>/P12 and TxD0/KR4/<TxD6>/P13 pins as general-purpose port pins, see

CHAPTER 4 PORT FUNCTIONS.