WHAT IS THE SSI INTERFACE?！

The continuous evolution of the automation field implies a growing request for precision in measurement devices and, therefore, also in absolute encoders. To satisfy this demand, absolute encoders have been designed with always higher resolution, which means an increasing number of bits and, as a consequence, also of wires.

The Synchronous Serial Interface (SSI) was created to solve these setbacks, in order to contain installation costs and simplify the wiring. This interface transmits data in a serial mode by using only two signals (CLOCK and DATA), independently from the number of bits of the encoder. 

The position data is obtained by the encoder reading system and continuously transmitted to a parallel/serial converter (based by a “shift register” with parallel loading). When the mono-stable circuit is activated by a clock signal transition, the data is stored and transmitted to the output synchronized with the clock signal.

CLOCK and DATA signals are transmitted differentially (RS422) to enhance immunity from interference and to allow longer transmission distances.

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