
243
μPD780948, μPD78F0948, μPD780949, μPD78F0949
17.2 Serial Interface UART Configuration
The UART includes the following hardware.
Table 17-1: Configuration of UART
Item
Configuration
Registers
Transmit shift register 1 (TXS0)
Receive shift register 1 (RXS0)
Receive buffer register (RXB0)
Control registers
Asynchronous serial interface mode register (ASIM0)
Asynchronous serial interface status register (ASIS0)
Baud rate generator control register (BRGC0)
(1) Transmit shift register 1 (TXS0)
This register is for setting the transmit data. The data is written to TXS0 for transmission as serial data.
When the data length is set as 7 bits, bits 0 to 6 of the data written to TXS0 are transmitted as serial
data. Writing data to TXS0 starts the transmit operation.
TXS0 can be written via 8-bit memory manipulation instructions. It cannot be read.
When RESET is input, its value is FFH.
Caution:
Do not write to TXS0 during a transmit operation.
The same address is assigned to TXS0 and the receive buffer register (RXB0). A read
operation reads values from RXB0.
(2) Receive shift register 1 (RXS0)
This register converts serial data input via the RxD pin to parallel data. When one byte of the data is
received at this register, the receive data is transferred to the receive buffer register (RXB0).
RXS0 cannot be manipulated directly by a program.
(3) Receive buffer register (RXB0)
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 (RXS0).
When the data length is set as 7 bits, receive data is sent to bits 0 to 6 of RXB0. The MSB must be
set to “0” in RXB0.
RXB0 can be read to via 8-bit memory manipulation instructions. It cannot be written to.
When RESET is input, its value is FFH.
Caution:
The same address is assigned to RXB0 and the transmit shift register (TXS0). During
a write operation, values are written to TXS0.
(4) Transmission control circuit
The transmission 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 (TXS0), based on the values set to the
asynchronous serial interface mode register (ASIM0).
(5) Reception control circuit
The reception control circuit controls the receive operations based on the values set to the asynchronous
serial interface mode register (ASIM0). During a receive operation, it performs error checking, such as
parity errors, and sets various values to the asynchronous serial interface status register (ASIS0) according
to the type of error that is detected.