Hitachi H8/3672 Series Hardware Manual page 202

Start transmission
[1] Read TDRE flag in SSR
Write transmit data to TDR
[2] All data transmitted?
Read TEND flag in SSR
Clear TE bit in SCR3 to 0
Figure 13-11 Sample Serial Transmission Flowchart(Clocked Synchronous Mode)
Rev. 1.0, 03/01, page 178 of 280
No
TDRE = 1
Yes
No
Yes
No
TEND = 1
Yes
<End>
[1] Read SSR and check that the TDRE flag is
set to 1, then write transmit data to TDR
and clear the TDRE flag to 0. When data is
written to TDR, the TDRE flag is
automatically cleared to 0 and clocks are
output to start the data transmission.
[2] To continue serial transmission, be sure to
read 1 from the TDRE flag to confirm that
writing is possible, then write data to TDR.
When data is written to TDR, the TDRE flag
is automatically cleared to 0.