Hitachi H8/3032 Series Hardware Manual page 367

In transmitting serial data, the SCI operates as follows.
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Serial transmit data is transmitted in the following order from the TxD pin:
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Figure 11-11 shows an example of SCI transmit operation using a multiprocessor format.
Figure 11-11 Example of SCI Transmit Operation (8-Bit Data with Multiprocessor Bit and
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The SCI monitors the TDRE flag in SSR. When the TDRE flag is cleared to 0 the SCI
recognizes that TDR contains new data, and loads this data from TDR into TSR.
After loading the data from TDR into TSR, the SCI sets the TDRE flag to 1 and starts
transmitting. If the TIE bit in SCR is set to 1, the SCI requests a transmit-data-empty interrupt
(TXI) at this time.
— Start bit: One 0 bit is output.
— Transmit data: 7 or 8 bits are output, LSB first.
— Multiprocessor bit: One multiprocessor bit (MPBT value) is output.
— Stop bit: One or two 1 bits (stop bits) are output.
— Mark state: Output of 1 bits continues until the start bit of the next transmit data.
The SCI checks the TDRE flag when it outputs the stop bit. If the TDRE flag is 0, the SCI
loads data from TDR into TSR, outputs the stop bit, then begins serial transmission of the
next frame. If the TDRE flag is 1, the SCI sets the TEND flag in SSR to 1, outputs the stop
bit, then continues output of 1 bits in the mark state. If the TEIE bit is set to 1 in SCR, a
transmit-end interrupt (TEI) is requested at this time.
Start
1 Data
bit
Serial
0 D0 D1
data
TDRE
TEND
TXI TXI interrupt handler
request writes data in TDR and
clears TDRE flag to 0
1 frame
Multi-
processor
bit
Stop Start
Data
bit bit
D7 0/1 1 0 D0 D1
TXI
request
One Stop Bit)
352
Multi-
processor
bit
Stop
1
bit
D7 0/1 1 Idle (mark)
state
TEI request