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CHAPTER 9 8-BIT SERIAL I/O
9.3.2 Serial Data Register (SDR)
The serial data register (SDR) stores the transfer data for 8-bit serial I/O.
The register can function as the transmit data register for serial output operation or as
the receive data register for serial input operation.
■ Serial data register (SDR)
Figure 9.3-4 "Serial data register (SDR)" shows the bit structure of the serial data register.
Figure 9.3-4 Serial data register (SDR)
●
Serial output operation
The register functions as the transmit data register. When serial I/O transfer starts (SMR: SST = "1"), the 8-
bit serial I/O performs serial transfer of the data written in the register.
●
Serial input operation
The register functions as the receive data register. When serial I/O transfer starts (SMR: SST = "1"), the
received serial transfer data is stored in this register.
●
During serial I/O transfer
Do not write data to the SDR register during serial I/O transfer operating. Also, the read value has no
meaning.
Register Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Initial value
SDR 001DH XXXXXXXX
B
R/W R/W R/W R/W R/W R/W R/W R/W
R/W : Readable and writable
X : Indeterminate