Synchronous Serial Interface (SSI)

The synchronous serial interface is a digital interface for absolute position and rotary measuring systems. It enables position and angular information to be transmitted digitally, absolutely and without bus overhead. As a result, it is especially well-suited for applications in which reliability and signal robustness are required in an industrial environment.

Transmission is synchronous to the request of the controller, and one bit of the position value to be output is transferred with each clock pulse.


The clock/data signals are transferred differentially via an RS 422 interface. Data formats are binary or Gray-encoded with a 24 or 25-bit position resolution.
A parity bit for increased data security can also be attached to the data format ("SSI26"). Possible clocking frequencies are in the range from 60 kHz to 2 MHz, and update rates of up to 16 kHz can be achieved. The maximum achievable clocking frequency is dependent on the cable length and the driver blocks used. This makes the SSI interface reliable, dynamic and inexpensive.