Datasheet

clock is high or low. To transmit data, both SPI peripherals must have identical serial clock phase (SCPH) and clock
polarity (SCPOL) values. The data frame can be 4 to 16/32 bits (depending upon SSI_MAX_XFER_SIZE) in length.
When the configuration parameter SCPH = 0, data transmission begins on the falling edge of the slave select signal.
The first data bit is captured by the master and slave peripherals on the first edge of the serial clock; therefore, valid
data must be present on the txd and rxd lines prior to the first serial clock edge.
Figure 124 shows a timing diagram for a single SPI data transfer with SCPH = 0. The serial clock is shown for
configuration parameters SCPOL = 0 and SCPOL = 1.
sclk_out/in 0
sclk_out/in 1
txd
rxd
ss_0_n/ss_in_n
ssi_oe_n
MSB
4 -32 bits
LSB
MSB LSB
Figure 124. SPI Serial
Format (SCPH = 0)
The following signals are illustrated in the timing diagrams in this section:
sclk_out
serial clock from DW_apb_ssi master
ss_0_n
slave select signal from DW_apb_ssi master
ss_in_n
slave select input to the DW_apb_ssi slave
ss_oe_n
output enable for the DW_apb_ssi master
txd
transmit data line for the DW_apb_ssi master
rxd
receive data line for the DW_apb_ssi master
Continuous data transfers are supported when SCPH = 0:
•
When CTRLR0. SSTE is set to 1, the DW_apb_ssi toggles the slave select signal between frames and the serial
clock is held to its default value while the slave select signal is active; this operating mode is illustrated in Figure
125.
sclk_out/in 0
sclk_out/in 1
txd/rxd
ss_0_n/ss_in_n
ssi_oe_n
MSBLSB LSB MSB
Figure 125. Serial
Format Continuous
Transfers (SCPH = 0)
When the configuration parameter SCPH = 1, master peripherals begin transmitting data on the first serial clock edge
after the slave select line is activated. The first data bit is captured on the second (trailing) serial clock edge. Data are
propagated by the master peripherals on the leading edge of the serial clock. During continuous data frame transfers,
the slave select line may be held active-low until the last bit of the last frame has been captured.
RP2040 Datasheet
4.10. SSI 601