W5500 Datasheet, PDF (24/65 Pages) List of Unclassifed Manufacturers – Supports 8 independent sockets simultaneously

2.4
Fixed Length Data Mode (FDM)
The FDM mode can be used when the External Host cannot control SCSn signal.
The SCSn signal should be tied to Low (Always connected to GND) and it cannot be
shared the SPI Bus with other SPI Devices. (Refer to the Figure 5.)
The SCSn signal should be tied to Low (Always connected to GND) and it is not
possible to share the SPI Bus with other SPI Devices. (Refer to the Figure 5.)
In VDM mode, Data Phase length is controlled by SCSn control.
But in FDM mode, Data Phase length is controlled by OM[1:0] value („01‟ / „10‟ / „11‟)
which is the SPI Operation Mode Bits of the Control Phase.
Because SPI Frame of FDM mode is the same as SPI Frame of VDM mode (1Byte, 2
Bytes, 4 Bytes SPI Frame) except the SCSn signal control and OM[1:0] setting, detail
description will be omitted.
As the SPI Frame of FDM mode is the same as SPI Frame of VDM mode (1Byte, 2
Bytes, 4 Bytes SPI Frame) except for the SCSn signal control and OM[1:0] setting, the
detail about FDM mode is not described in this section.
It is not recommended to use the FDM mode unless you are in inevitable status. In
addition, we use only 1/2/4 Bytes SPI Frame, as described in „Chapter 2.4.1‟ &
„Chapter 2.4.2‟. Using SPI Frame with other length of Data will cause malfunction of
W5500.
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W5500 Datasheet Version1.0 (August 2013)