National Semiconductor Microwire Frame Format - Wiznet W7500 Reference Manual

If the PrimeCell SSP is enabled and there is valid data within the transmit FIFO, the start of
transmission is signified by the SSPFSSOUT master signal being driven LOW. The nSSPOE line is
driven LOW, enabling the master SSPTXD output pad. After an additional one half SSPCLKOUT
period, both master and slave data are enabled onto their respective transmission lines. At
the same time, the SSPCLKOUT is enabled with a falling edge transition. Data is then captured
on the rising edges and propagated on the falling edges of the SSPCLKOUT signal.
After all bits have been transferred in the case of a single word transmission, the SSPFSSOUT
line is returned to its idle HIGH state one SSPCLKOUT period after the last bit has been
captured.
For continuous back-to-back transmissions, the SSPFSSOUT pin remains in its active-LOW state,
until the final bit of the last word has been captured, and then returns to its idle state as the
previous section describes.
For continuous back-to-back transfers, the SSPFSSOUT pin is held LOW between successive
data words and termination is the same as that of the single word transfer.

National Semiconductor Microwire frame format

Figure 65 shows the National Semiconductor Microwire frame format for a single frame.
SSPCLKOUT/
SSPCLKIN
SSPFSSOUT/
SSPFSSIN
SSPTXD
SSPRXD
nSSPOE
Figure 65.
Microwire format is very similar to the SPI format except that transmission is half-duplex
instead of full-duplex using a master-slave message passing technique. Each serial transmission
begins with an 8-bit control word that is transmitted from the PrimeCell SSP to the off-chip
slave device. During this transmission, the PrimeCell SSP receives no incoming data. After the
message has been sent, the off-chip slave decodes it and responds with the required data after
waiting one serial clock after the last bit of the 8-bit control message has been sent. The
W7500x Reference Manual Version1.1.0
MSB
8-bit control
National Semiconductor Microwire frame format, single transfer
LSB LSB
4 to 16 bits
output data
0 MSB MSB LSB LSB LSB
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