30.4.3.3 Host with Several Clients

A host with multiple clients in parallel is only available when Host SPI Select Enable (CTRLB.MSSEN) is set to ‘0’, disabling hardware SS control. If the bus consists of several SPI clients, the SPI host can use general purpose I/O pins to control the SS line for each client on the bus, as shown in the following figure. In this configuration, only the selected SPI client will drive the MISO line.

Another configuration is multiple clients in series, as shown in the following figure. In this setup, all n attached clients are connected to the same SS line. Depending on the Host SPI Select Enable bit (CTRLB.MSSEN), the SS line can be controlled either by hardware or by user software using normal GPIO. The host must shift n characters for a complete transaction.