R01UH0823EJ0100 Rev.1.00
Page 1370 of 1823
Jul 31, 2019
RX23W Group
38. Serial Peripheral Interface (RSPIa)
(4) LSB First Transfer (24-Bit Data)
shows details of operations by the RSPI data register (SPDR) and the shift register in transfer with parity
disabled, 24 bits as the RSPI data length for an example that is not 32 bits, and LSB first selected.
In transmission, the lower-order 24 bits (T23 to T00) from the current stage of the transmit buffer are reordered bit by bit
to obtain the order T00 to T23 for copying to the shift register. Data for transmission are shifted out from the shift register
in order from T00, through T01, and so on to T23.
In reception, received data are shifted in bit by bit through bit 8 of the shift register. When bits R00 to R23 have been
collected after input of the required number of cycles of RSPCK, the value in the shift register is copied to the receive
buffer.
At this time, the higher-order 8 bits of the transmit buffer are stored in the higher-order 8 bits of the receive buffer.
Writing 0 to bits T31 to T24 at the time of transmission leads to 0 being inserted in the higher-order 8 bits of the receive
buffer.
Figure 38.17
LSB First Transfer (24-Bit Data, Parity Disabled)
R00
R01
R02
R03
R04
R05
R06
R07
R08
T25
T26
T27
T28
T29
T30
T31
T31
T30
T29
T28
T27
T26
T25
T24
R23
R06
R05
R23
T24
R08
R07
R04
R03
R02
R01
R00
Input
Transfer start
Transfer end
Bit 31
Bit 0
T31
T30
T29
T28
T27
T26
T25
T24
T23
T06
T05
T04
T03
T02
T01
T00
T00
T01
T02
T03
T04
T05
T06
T07
T08
T25
T26
T27
T28
T29
T30
T31
T08
T07
T23
T24
Receive buffer
Transmit buffer
Shift register
Shift register
Output
Copy
Copy
Bit 31
Bit 0
Bit 31
Bit 0
Bit 31
Bit 0
Note: Output = MOSI (master)/MISO (slave), input = MISO (master)/MOSI (slave)