R01UH0823EJ0100 Rev.1.00
Page 1368 of 1823
Jul 31, 2019
RX23W Group
38. Serial Peripheral Interface (RSPIa)
(2) MSB 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 MSB first selected.
In transmission, the lower-order 24 bits (T23 to T00) from the current stage of the transmit buffer are copied to the shift
register. Data for transmission are shifted out from the shift register in order from T23, through T22, and so on to T00.
In reception, received data are shifted in bit by bit through bit 0 of the shift register. When bits R23 to R00 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 38.15
MSB First Transfer (24-Bit Data, Parity Disabled)
Output
Transfer start
Transfer end
T31
T30
T29
T28
T27
T26
T25
T24
T23
T06
T05
T04
T03
T02
T01
T00
T31
T30
T29
T28
T27
T26
T25
T24
T23
T31
T30
T29
T28
T27
T26
T25
T24
R23
T31
T30
T29
T28
T27
T26
T25
T24
R23
T06
T05
T04
T03
T02
T01
T00
R06
R05
R04
R03
R02
R01
R00
R06
R05
T08
T07
T08
T07
R08
R07
R08
R07
R04
R03
R02
R01
R00
Shift register
Copy
Shift register
Input
Copy
Bit 0
Receive buffer
Bit 31
Bit 24
Bit 23
Bit 0
Bit 31
Bit 24
Bit 23
Bit 0
Bit 31
Bit 23
Transmit buffer
Bit 0
Bit 31
Bit 23
Note: Output = MOSI (master)/MISO (slave), input = MISO (master)/MOSI (slave)