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CHAPTER 14 8-BIT SERIAL I/O
14.4.2 Serial Data Register (SDR)
The serial data register (SDR) retains 8-bit serial I/O transfer data. The SDR functions as
a transmission data register at serial output operation. It functions as a reception data
register at serial input operation.
■ Serial Data Register (SDR)
Figure 14.4-3 shows the bit structure of the SDR.
Figure 14.4-3 Serial Data Register (SDR)
● At serial output operation
The SDR functions as a transmission data register at serial output operation. When serial I/O transfer is
started (SMR: SST = 1), the 8-bit serial data written to the SDR is transferred. Transmission data does not
remain in the SDR because it is shifted out via serial I/O transfer.
● At serial input operation
The SDR functions as a reception data register. When serial I/O transfer is started (SMR: SST = 1), the
serially transferred reception data is stored in the SDR.
● When the serial I/O is in transfer operation
When the serial I/O is in transfer operation, do not write data to the SDR. Moreover, note that the read
values have no significance.
When serial output and serial input are allowed at the same time, serial I/O operation is performed.
bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0
003A
H
XXXXXXXX
B
R/W R/W R/W R/W R/W R/W R/W R/W
R/W : Readable and Writable
X : Undefined
Address
Initial value