Datasheet

sclk_out
txd
rxd
ss_0_n
ssi_oe_n
MSB LSB
Control word
MSB
LSB
Data word 0
Figure 136. Single
Microwire Transfer
(transmitting data
frame)

NOTE
The DW_apb_ssi does not support continuous sequential Microwire writes, where MDD = 1 and MWMOD = 1.
Figure 137 shows how the data and control frames are structured in the transmit FIFO prior to the transfer, also shown is
the value programmed into the MWCR register.
0
Tx FIFO Buffer
FIFO Status Prior to
Transfer
FIFO Status on
Completion of Transfer
Rx FIFO Buffer
MWHS
MWCR
Location n
Location 3
Location 2
Location 1
Location 0
Location n
Location 3
Location 2
Location 1
Location 0
Write DR
NULL
NULL SHIFT LOGIC
NULL
Tx Data(0)
Ctrl Word(0)
Rx FIFO Empty
1
MDD
0
MWMOD
rxd
txd
NULL
NULL
NULL
NULL
NULL
Tx FIFO Empty
Figure 137. FIFO
Status for Single
Microwire Transfer
(transmitting data
frame)
Continuous transfers occur as shown in Figure 138, with the control word for the next transfer following immediately after
the LSB of the current data word.
sclk_out
txd
rxd
ss_0_n
ssi_oe_n
MSB LSB MSB LSB MSB LSB LSBMSB
Control word 0 Data word 1Data word 0 Control word 1
Figure 138.
Continuous Microwire
Transfer (transmitting
data frame)
The only modification you need to make to perform a continuous transfer is to write more control and data words into the
transmit FIFO buffer, shown in Figure 139. This example shows two data words are written to the external serial slave
device.
RP2040 Datasheet
4.11. SSI 608