Can SSI channels work in Slave mode, acting as a „listener“ to the existing data communication between encoder and servo amplifier?
It's a big problem to connect absolute encoder of servo to amplifier and to 7i74 simultaneously
It should be possible to do this but its awkward for a number of reasons:
1. isolation/noise: The drives encoder interface is often a much noisier environment than the drives host interface
its not really intended that these signals be tapped at this place
2. You would need 2 differential receiver interfaces without termination (not a problem but awkward wiring wise with a 7I44/7I74)
3. The servo drives encoder interface is asynchronous to LinuxCNC's sampling leading to beats and problems with
velocity estimation ( without added hardware to timestamp the servos reads )
4. Drives with absolute encoders usually have a way to read this absolute position
Some can be SSI slaves, others have a RS-232 or RS-485 interface that is used at startup, and of course drives
with real-time bidirectional interfaces (Ethercat, Sercos, Ethernet Powerlink, etc) can provide real time absolute position
to the host as part of the process data interchange
