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.
I Serial data register (SDR)
Figure 9.3-4 "Serial data register (SDR)" shows the bit structure of the serial data register.
Register
SDR
R/W : Readable and writable
X
: Indeterminate
G
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.
G
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.
G
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.
Figure 9.3-4 Serial data register (SDR)
Address
Bit 7
Bit 6
001DH
R/W
R/W
Bit 5
Bit 4
Bit 3
Bit 2
R/W
R/W
R/W
R/W
CHAPTER 9 8-BIT SERIAL I/O
Bit 1
Bit 0
Initial value
XXXXXXXX
B
R/W
R/W
179