Uart Configuration - NEC mPD780973 Series Preliminary User's Manual

14.2 UART Configuration

The UART consists of the following hardware.
Item
Registers
Control registers
(1) Transmit shift register (TXS)
This is the register for setting transmit data. Data written to TXS is transmitted as serial data.
When the data length is set as 7 bits, bits 0 to 6 of the data written to TXS are transmitted as transmit data. Writing
data to TXS starts the transmit operation.
TXS is written with an 8-bit memory manipulation instruction. It cannot be read.
When RESET is input, its value is FFH.
Caution Do not write to TXS during a transmit operation.
The same address is assigned to TXS and the receive buffer register (RXB). A read
operation reads values from RXB.
(2) Receive shift register (RXS)
This register converts serial data input via the RxD pin to parallel data. When one byte of data is received at
this register, the receive data is transferred to the receive buffer register (RXB).
RXS cannot be manipulated directly by a program.
(3) Receive buffer register (RXB)
This register is used to hold receive data. When one byte of data is received, one byte of new receive data is
transferred from the receive shift register (RXS).
When the data length is set as 7 bits, receive data is transferred to bits 0 to 6 of RXB. In RXB, the MSB must
be set to 0.
RXB is read with an 8-bit memory manipulation instruction. It cannot be written to.
When RESET is input, its value is FFH.
Caution The same address is assigned to RXB and the transmit shift register (TXS). During a write
operation, values are written to TXS.
(4) Transmit control circuit
The transmit control circuit controls transmit operations, such as adding a start bit, parity bit, and stop bit to data
that is written to the transmit shift register (TXS), based on the values set to the asynchronous serial interface
mode register (ASIM).
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CHAPTER 14 SERIAL INTERFACE UART
Table 14-1. UART Configuration
Configuration
Transmit shift register (TXS)
Receive shift register (RXS)
Receive buffer register (RXB)
Asynchronous serial interface mode register (ASIM)
Asynchronous serial interface status register (ASIS)
Baud rate generator control register (BRGC)