Datasheet

Table Of Contents
Section 13 Serial Communication Interface
Page 442 of 846 REJ09B0140-0900 Rev. 9.00
Sep 16, 2010
H8S/2215 Group
2. After transferring data from TDR to TSR, the SCI sets the TDRE flag to 1 and starts
transmission. If the TIE bit in SCR is set to 1 at this time, a transmit data empty interrupt (TXI)
is generated. Continuous transmission is possible because the TXI interrupt routine writes the
next transmit data to TDR before transmission of the current transmit data has been completed.
3. 8-bit data is sent from the TxD pin synchronized with the output clock when output clock
mode has been specified, and synchronized with the input clock when use of an external clock
has been specified.
4. The SCI checks the TDRE flag at the timing for sending the MSB (bit 7).
5. If the TDRE flag is cleared to 0, data is transferred from TDR to TSR, and serial transmission
of the next frame is started.
6. If the TDRE flag is set to 1, the TEND flag in SSR is set to 1, and the TDRE flag maintains the
output state of the last bit. If the TEIE bit in SCR is set to 1 at this time, a TEI interrupt request
is generated. The SCK pin is fixed high.
Figure 13.21 shows a sample flow chart for serial data transmission. Even if the TDRE flag is
cleared to 0, transmission will not start while a receive error flag (ORER, FER, or PER) is set to 1.
Make sure that the receive error flags are cleared to 0 before starting transmission. Note that
clearing the RE bit to 0 does not clear the receive error flags.
Transfer direction
Bit 0
Serial data
Synchronization
clock
1 frame
TDRE
TEND
Data written to TDR and
TDRE flag cleared to 0 in
TXI interrupt service
routine
TXI interrupt request
generated
Bit 1
Bit 7 Bit 0 Bit 1 Bit 6 Bit 7
TXI interrupt request
generated
TEI interrupt request
generated
Figure 13.20 Sample SCI Transmission Operation in Clocked Synchronous Mode