R01UH0823EJ0100 Rev.1.00 Page 1378 of 1823
Jul 31, 2019
RX23W Group 38. Serial Peripheral Interface (RSPIa)
38.3.6.2 Transmit Operations Only (SPCR.TXMD = 1)
Figure 38.25 shows an example of operation when the communications operating mode select bit (SPCR.TXMD) is set
to 1. In the example in
Figure 38.25, the RSPI performs an 8-bit serial transfer in which the SPDCR.SPFC[1:0] bits are
00b, the SPCMDm.CPHA bit is 1, and the SPCMDm.CPOL bit is 0. The numbers given under the RSPCKA waveform
represent the number of RSPCK cycles (i.e., the number of transferred bits).
Figure 38.25 Operation Example of SPCR.TXMD = 1
The operation of the flags at timings shown in steps (1) to (3) in the figure is described below.
(1) Make sure there is no data left in the receive buffer and the SPSR.SPRF, OVRF flags are 0 before entering the mode
of transmit operations only (SPCR.TXMD = 1).
(2) When a serial transfer ends with the receive buffer of SPDR empty, if the mode of transmit operations only is
selected (SPCR.TXMD = 1), the SPRF flag remains 0 and the RSPI does not copy the data from the shift register to
the receive buffer.
(3) Since the receive buffer of SPDR does not hold data that was received in the previous serial transfer, even when a
serial transfer ends, the SPSR.OVRF flag retains the value of 0, and the data in the shift register is not copied to the
receive buffer.
When performing transmit operations only (SPCR.TXMD = 1), the RSPI transmits data but does not receive data.
Therefore, the SPSR.SPRF, OVRF flags remain 0 at the timings of (1) to (3).
W W
SPDR access
OVRF
SPRI
87654321 87654321
(3)
(2)
TXMD
(TXMD = 1)
Empty
Receive buffer status
(1)
SPRF
(CPHA = 1, CPOL = 0)
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