SSI interface discription of absolute encoder！

The SSI interface permits the transfer of the absolute encoder position information through a serial line, synchronised with
a clock. The following figure shows the block diagram of an encoder with an SSI interface:
The encoder with an SSI interface is constituted by the classic absolute encoder position measurement system including:
a light source, a disc with transparent and opaque zones, photo-electric receivers, comparison/trigger circuits, a parallel/serial converter, a mono-stable circuit, an input circuit for the clock signal and by an output driver for the data signal.
The value of the position is taken by the encoder reading system and continually sent to a parallel/serial converter (constituted essentially of a “shift register” with parallel loading). When the mono-stable circuit is activated by a clock signal
transition, the data is memorised and sent to the output, scheduled according to the clock’s own signal. The CLOCK and DATA signals are transmitted differentially (RS422) to increase immunity from interference and to be able to support long
transmission distances.
CLOCK signal circuit input DATA signal circuit output
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