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11.2.3 Transmit Shift Register (TSR)
TSR is an 8-bit register used to transmit serial data.
Bit
Read/Write
The SCI loads transmit data from TDR into TSR, then transmits the data serially from the TxD
pin, LSB (bit 0) first. After transmitting one data byte, the SCI automatically loads the next
transmit data from TDR into TSR and starts transmitting it. If the TDRE flag is set to 1 in SSR,
however, the SCI does not load the TDR contents into TSR. The CPU cannot read or write TSR
directly.
11.2.4 Transmit Data Register (TDR)
TDR is an 8-bit register that stores data for serial transmission.
Bit
Initial value
Read/Write
R/W
When the SCI detects that TSR is empty, it moves transmit data written in TDR from TDR into
TSR and starts serial transmission. Continuous serial transmission is possible by writing the next
transmit data in TDR during serial transmission from TSR.
The CPU can always read and write TDR. TDR is initialized to H'FF by a reset and in standby
mode.
332
7
6
—
—
7
6
1
1
R/W
R/W
5
4
—
—
5
4
1
1
R/W
R/W
3
2
—
—
3
2
1
1
R/W
R/W
1
0
—
—
1
0
1
1
R/W
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