Serial Data Transmission (Asynchronous Mode) - Renesas RZ/A Series User Manual

RZ/A1L Group, RZ/A1LU Group, RZ/A1LC Group
15.3.6

Serial Data Transmission (Asynchronous Mode)

Figure 15.6 shows an example of the operation for serial transmission in asynchronous mode.
In serial transmission, the SCI operates as described below.
1. The SCI transfers data from TDR to TSR when data is written to TDR in the TXI interrupt processing routine. The
TXI interrupt request at the beginning of transmission is generated when the TE bit in SCR is set to 1 after the TIE
bit in SCR is set to 1 or when these two bits are set to 1 simultaneously by a single instruction.
2. Transmission starts after the CTSE bit in SECR is set to 0 (disabling the CTS function) and a low level on the CTS#
pin causes data transfer from TDR to TSR. If the TIE bit in SCR is 1 at this time, a TXI interrupt request is
generated. Continuous transmission is obtainable by writing the next data for transmission to TDR in the TXI
interrupt processing routine before transmission of the current data for transmission is completed. When TEI
interrupt requests are in use, set the SCR.TIE bit to 0 (disabling TXI requests) and the SCR.TEIE bit to 1 (enabling
TEI requests) after the last of the data to be transmitted are written to the TDR from the processing routine for TXI
requests.
3. Data is sent from the TXDn pin in the following order: start bit, transmit data, parity bit or multi-processor bit (may
be omitted depending on the format), and stop bit.
4. The SCI checks for updating of (writing to) TDR at the time of stop bit output.
5. When TDR is updated, setting of the CTSE bit in SECR to 0 (CTS function disabled) or a low level input on the
CTSn# pin cause the next transfer of the next data for transmission from TDR to TSR and sending of the stop bit,
after which serial transmission of the next frame starts.
6. If TDR is not updated, the TEND flag in SSR is set to 1, the stop bit is sent, and then the mark state is entered in
which 1 is output. If the TEIE flag in SCR is 1 at this time, the TEND flag in SSR is set to 1 and a TEI interrupt
request is generated.
Figure 15.7 shows a sample flowchart for serial transmission in asynchronous mode.
Start bit
1 0
TXI interrupt flag
SSR.TEND flag
TXI interrupt
request
generated
Figure 15.6 Example of Operation for Serial Transmission in Asynchronous Mode (from the Middle of
Transmission until Transmission Completion) (Example with 8-Bit Data, Parity, One Stop Bit)
R01UH0437EJ0600 Rev.6.00
Jan 29, 2021
Parity bit Stop bit
Data
D0 D1 D7 0/1 1 0
(TIE = 1)
Data written to
TXI interrupt
TDR in TXI request
interrupt
generated
processing
routine
1 frame
D0 D1 D7 0/1 1 0
(TIE = 0)
Data written to TDR in TXI
interrupt processing routine
(Set the TIE bit to 0 and the
TEIE bit to 1 after writing the
last data)
15. Serial Communications Interface
Idle state
D0 D1 D7 0/1 1
(mark state)
TEI interrupt
request generated
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