SPI: Serial Peripheral Interface Daisy Chain

Daisy-chaining slave devices in a Serial Peripheral Interface (SPI) can reduce the complexity and board layout of large systems. It is another extremely popular method used in the professional industry.

Usually the addition of a slave device results in the addition of a slave select (SS) control line. In a large system consisting of many slave devices, it can increase the board space and complexity. Daisy chaining is one method to reduce this complexity.

As you can see, the slave units are daisy chained with their MOSI and MISO pins connected together. At each clock pulse, a bit of data enters each of the devices through its input pin and another bit from the serial shift register exits. The same data and commands propagate through all the slave units.

Since each bit of data filters through successive slave units, the slave units will possess different data at any one time. Each slave unit will be 1 bit behind, and this may pose an issue if your design requires all the slave units to have the same data at the same time.

The SS pin on the slave units is typically active low and tied to a single control line. In this configuration, all the slave units need to have their SS pins set to the active mode since they all receive the same data.

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