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CHAPTER 11 SERIAL INTERFACE
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11.2 Serial Interface Configuration
The serial interface (UART00) consists of the following hardware.
Table 11-1. Serial Interface Configuration
Item
Configuration
Register
Transmission shift register 00 (TXS00)
Reception shift register 00 (RXS00)
Reception buffer register 00 (RXB00)
Control register
Asynchronous serial interface mode register 00 (ASIM00)
Asynchronous serial interface status register 00 (ASIS00)
Baud rate generator control register 00 (BRGC00)
(1)
Transmission shift register 00 (TXS00)
TXS00 is a register in which transmission data is prepared. The transmission data is output from TXS00
bit-serially.
When the data length is seven bits, bits 0 to 6 of the data in TXS00 will be transmission data. Writing data
to TXS00 triggers transmission.
TXS00 can be write-accessed, using an 8-bit memory manipulation instruction, but cannot be read-
accessed.
RESET input loads FFH into TXS00.
Caution
Do not write to TXS00 during transmission.
TXS00 and reception buffer register 00 (RXB00) are mapped at the same address, such
that any attempt to read from TXS00 results in a value being read from the RXB00.
(2)
Reception shift register 00 (RXS00)
RXS00 is a register in which serial data, received at the RxD00 pin, is converted to parallel data. Once one
entire byte has been received, RXS00 feeds the reception data to reception buffer register 00 (RXB00).
RXS00 cannot be manipulated directly by a program.
(3)
Reception buffer register 00 (RXB00)
RXB00 is used to hold reception data. Once reception shift register 00 (RXS00) has received one entire
byte of data, it feeds that data into RXB00.
When the data length is seven bits, the reception data is sent to bits 0 to 6 of RXB00, in which the MSB is
fixed to 0.
RXB00 can be read-accessed, using an 8-bit memory manipulation instruction, but cannot be write-
accessed.
RESET input loads FFH into RXB00.
Caution
RXB00 and transmission shift register 00 (TXS00) are mapped at the same address, such
that any attempt to write to RXB00 results in a value being written to TXS00.
(4)
Transmission control circuit
The transmission control circuit controls transmission. For example, it adds start, parity, and stop bits to the
data in transmission shift register 00 (TXS00), according to the setting of asynchronous serial interface
mode register 00 (ASIM00).