JVL MIS17 Series User Manual page 121

5.7 SSI encoder/sensor interface
5.7.4 The SSI interface principle of operation.
When the differential lines are used for SSI, the A1+/- lines work as a clock signal to the
encoder, while the B1+/- signals work as a data signal from the encoder to the controller
(MISxxx/SMCxx).
The figure above shows the SSI protocol principle.
The clock line is normally high. When a reading is requested, the clock goes low for t1
micro seconds (see illustration above) to allow the encoder to sample and prepare a val-
ue.
On the first rising edge of the clock (1), no sampling is done but on the second rising edge
of the clock (2) the first data bit is read from the data line.
Shortly after reading the bit value, the MISxxx/SMCxx will set the clock high and execute
another cycle, where the data bit is sampled just before each rising clock.
After the last data bit has been sampled, the clock stays high.
Se also Setup and operation of the SSI function when using MacTalk., page 117 where a
sample program is shown.
JVL Industri Elektronik A/S - User Manual - Integrated Stepper Motors MIS17x, 23x, 34x, 43x 121