Renesas H8S Series Hardware Manual page 521

• Serial data transmission (asynchronous mode)
Figure 14-5 shows a sample flowchart for serial transmission.
The following procedure should be used for serial data transmission.
and clear TDRE flag in SSR to 0
In serial transmission, the SCI operates as described below.
[1] The SCI monitors the TDRE flag in SSR, and if is 0, recognizes that data has been written to TDR, and transfers the
data from TDR to TSR.
[2] After transferring data from TDR to TSR, the SCI sets the TDRE flag to 1 and starts transmission.
If the TIE bit is set to 1 at this time, a transmit data empty interrupt (TXI) is generated.
The serial transmit data is sent from the TxD pin in the following order.
[a] Start bit:
One 0-bit is output.
Initialization
Start transmission
Read TDRE flag in SSR
TDRE=1
Yes
Write transmit data to TDR
All data transmitted?
Yes
Read TEND flag in SSR
TEND= 1
Yes
Break output?
Yes
Clear DR to 0 and
set DDR to 1
Clear TE bit in SCR to 0
<End>
Figure 14-5 Sample Serial Transmission Flowchart
[1] SCI initialization:
[1]
The TxD pin is automatically
designated as the transmit data
output pin.
After the TE bit is set to 1, a frame
of 1s is output, and transmission is
[2]
enabled.
[2] SCI status check and transmit data
No
write:
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.
[3] Serial transmission continuation
procedure:
To continue serial transmission,
No
read 1 from the TDRE flag to
confirm that writing is possible,
then write data to TDR, and then
clear the TDRE flag to 0. Checking
[3]
and clearing of the TDRE flag is
automatic when the DMAC or DTC
is activated by a transmit data
empty interrupt (TXI) request, and
No
data is written to TDR.
[4] Break output at the end of serial
transmission:
To output a break in serial
No
[4]
transmission, set DDR for the port
corresponding to the TxD pin to 1,
clear DR to 0, then clear the TE bit
in SCR to 0.
Rev.6.00 Oct.28.2004 page 493 of 1016
REJ09B0138-0600H