Uart Operations; Operation Stop Mode; Asynchronous Serial Interface (Uart) Mode - NEC mPD780973 Series Preliminary User's Manual

14.4 UART Operations

This section explains the two modes of the UART.

14.4.1 Operation stop mode

This mode is used when serial transfers are not performed to reduce power consumption.
In the operation stop mode, P53/RxD and P54/TxD pins can be used as ordinary ports.
(1) Register settings
Operation stop mode settings are made via the asynchronous serial interface mode register (ASIM).
ASIM is set with a 1-bit or 8-bit memory manipulation instruction.
When RESET is input, its value is 00H.
Address: FF85H After Reset: 00H
Symbol 7
ASIM TXE
TXE
0
0
1
1
Cautions 1. Do not switch the operation mode until after the current serial transmit/receive operation
has stopped.
2. Bit 0 must be set to 0.

14.4.2 Asynchronous serial interface (UART) mode

This mode enables full-duplex operation wherein one byte of data is transmitted or received after the start bit.
The on-chip dedicated UART baud rate generator enables communications using a wide range of selectable baud
rates.
The UART baud rate generator can also be used to generate a MIDI-standard baud rate (31.25 kbps).
(1) Register settings
UART mode settings are made via the asynchronous serial interface mode register (ASIM), asynchronous serial
interface status register (ASIS), and the baud rate generator control register (BRGC).
CHAPTER 14 SERIAL INTERFACE UART
R/W
6 5 4
RXE PS1 PS0
RXE Operation Mode
0 Operation stop
1 UART mode
(receive only)
0 UART mode
(transmit only)
1 UART mode
(transmit and receive)
3 2
CL SL ISRM
RxD/P53 Pin Function TxD/P54 Pin Function
Port function Port function
Serial function Port function
Port function Serial function
Serial function Serial function
1 0
0
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