3069RF-ZTAT Datasheet, PDF (525/1003 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER

In transmitting serial data, the SCI operates as follows.
• 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 to TSR, the SCI sets the TDRE flag to 1 and starts
transmitting. If the TIE bit is set to 1 in SCR, the SCI requests a transmit-data-empty interrupt
(TXI) at this time.
If clock output is selected, the SCI outputs eight serial clock pulses. If an external clock
source is selected, the SCI outputs data in synchronization with the input clock. Data is output
from the TxD pin n order from LSB (bit 0) to MSB (bit 7).
• The SCI checks the TDRE flag when it outputs the MSB (bit 7). If the TDRE flag is 0, the
SCI loads data from TDR into TSR and begins serial transmission of the next frame. If the
TDRE flag is 1, the SCI sets the TEND flag to 1 in SSR, and after transmitting the MSB (bit
7), holds the TxD pin in the MSB state. If the TEIE bit is set to 1 in SCR, a transmit-end
interrupt (TEI) is requested at this time
• After the end of serial transmission, the SCK pin is held in a constant state.
Figure 13.17 shows an example of SCI transmit operation.
Serial clock
Transmit direction
Serial data
Bit 0 Bit 1
Bit 7 Bit 0 Bit 1
Bit 6 Bit 7
TDRE
TEND
TXI interrupt
request
TXI interrupt handler
writes data in TDR
and clears TDRE
flag to 0
TXI interrupt
request
1 frame
TEI interrupt
request
Figure 13.17 Example of SCI Transmit Operation
• Receiving Serial Data (Synchronous Mode): Figure 13.18 shows a sample flowchart for
receiving serial data and indicates the procedure to follow. When switching from
asynchronous to synchronous mode. make sure that the ORER, PER, and FER flags are
cleared to 0. If the FER or PER flag is set to 1 the RDRF flag will not be set and both
transmitting and receiving will be disabled.
Rev. 5.0, 09/04, page 503 of 978