In Host mode, the Client Select Disable (SSD) bit in the Control B (SPIn.CTRLB) register controls how the SPI uses the SS pin.
If SSD in SPIn.CTRLB is ‘0
’, the SPI can use the
SS pin to transition from Host to Client mode. This
allows multiple SPI hosts on the same SPI bus.
If SSD in SPIn.CTRLB is ‘0
’, and the SS pin
is configured as an output pin, it can be used as a regular I/O pin or by other
peripheral modules and will not affect the SPI system
If SSD in SPIn.CTRLB is ‘1
’, the SPI does not use the
SS pin. It can be used as a regular I/O pin or by other
peripheral modules.
0
’, and the SS
is configured as an input pin, the SS pin must be held high to
ensure Host SPI operation. A low level will be interpreted as another Host is trying to
take control of the bus. This will switch the SPI into Client mode, and the hardware of the
SPI will perform the following actions: SS Configuration | SS Pin-Level | Description |
---|---|---|
Input | High | Host activated (selected) |
Low | Host deactivated, switched to Client mode | |
Output | High | Host activated (selected) |
Low |