Transmit Shift Register (Tsr); Transmit Data Register (Tdr) - Hitachi H8S/2646 Hardware Manual

13.2.3

Transmit Shift Register (TSR)

Bit : 7
R/W : —
TSR is a register used to transmit serial data.
To perform serial data transmission, the SCI first transfers transmit data from TDR to TSR, then
sends the data to the TxD pin starting with the LSB (bit 0).
When transmission of one byte is completed, the next transmit data is transferred from TDR to
TSR, and transmission started, automatically. However, data transfer from TDR to TSR is not
performed if the TDRE bit in SSR is set to 1.
TSR cannot be directly read or written to by the CPU.
13.2.4

Transmit Data Register (TDR)

Bit :
Initial value :
R/W : R/W
TDR is an 8-bit register that stores data for serial transmission.
When the SCI detects that TSR is empty, it transfers the transmit data written in TDR to TSR and
starts serial transmission. Continuous serial transmission can be carried out by writing the next
transmit data to TDR during serial transmission of the data in TSR.
TDR can be read or written to by the CPU at all times.
TDR is initialized to H'FF by a reset, in standby mode, watch mode, subactive mode, and subsleep
mode or module stop mode.
6 5
— —
7 6 5
1 1 1
R/W R/W
4 3 2
— — —
4 3
1 1
R/W R/W
1 0
— —
2 1
1 1
R/W R/W R/W
0
1
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