NEC mPD789026 Subseries, User Manual

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CHAPTER 9 SERIAL INTERFACE 00
User's Manual U11919EJ3V0UM00
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(1) Transmit shift register 00 (TXS00)
This register is used to specify data to be transmitted. Data written to TXS00 is transmitted as serial data.
If the data length is specified as 7 bits, bits 0 to 6 of the data written to TXS00 are transferred as the
transmit data. The transmit operation is started by writing data to TXS00.
TXS00 is written to with an 8-bit memory manipulation instruction. It cannot be read.
RESET input sets TXS00 to FFH.
Caution Do not write to TXS00 during transmission.
TXS00 and receive buffer register 00 (RXB00) are allocated to the same address, and when
reading is performed, RXB00 values are read.
(2) Receive shift register 00 (RXS00)
This register is used to convert serial data input to the RxD pin into parallel data. Each time one byte of
data is received, it is transferred to receive buffer register 00 (RXB00).
RXS00 cannot be manipulated directly by program.
(3) Receive buffer register 00 (RXB00)
This register is used to hold received data. Each time one byte of data is received, a new byte of data is
transferred from receive shift register 00 (RXS00).
If the data length is specified as 7 bits, receive data is transferred to bits 0 to 6 of RXB00, and the MSB of
RXB00 always becomes 0.
RXB00 can be read with an 8-bit memory manipulation instruction. It cannot be written to.
RESET input makes RXB00 undefined.
Caution RXB00 and transmit shift register 00 (TXS00) are allocated to the same address, and when
writing is performed, the values are written to TXS00.
(4) Transmit control circuit
This circuit controls transmit operations by adding a start bit, parity bit, and stop bit to data written to
transmit shift register 00 (TXS00), according to the data set to asynchronous serial interface mode register
00 (ASIM00).
(5) Receive control circuit
This circuit controls receive operations according to the data set to asynchronous serial interface mode
register 00 (ASIM00). It performs also parity error check, etc., during receive operations, and when an error
is detected, it sets the value to asynchronous serial interface status register 00 (ASIS00) depending on the
nature of the error.