What interface is this encoder?

Hello,

I recently bought this encoder, Opkon MRA 50AR8 TT 12 SSI V2.
It says in the datasheet it is an SSI interface, however after having it here now I suddenly noticed there's no differential wire pairs.
Instead there is only a single DO pin, a clock pin and what seems to be chip select. This seems to point to something similar to SPI, but SPI normally has 2 data wires for bidirectional data. I am not sure if simply connecting data out to only MISO is what is intended here.

I was hoping someone here already came across something similar once before.

PDF files attached are the datasheets I was able to find online. The one starting with "datablad" is provided by the retailer, and the other one I found online, but contains some more information on the communication protocol.

It is SSI but TTL levels and having a CS pin are not standard
(sounds like the interface is directly from the encoder chip)

yes that is a serial protocol. Actually, such encoders are connected directly to the amplifier from the same manufacturer. Looks like a driver needs to be written for it. At the moment I don't know how to connect the thing. But it's a very interesting thing. Has anyone ever done something in this direction and can this show us?

it should be supported by HM2s SSI interface if you can simply tie CS in the active state.
TTL is not a great interface for encoders however as its quite susceptible to noise

PCW wrote:

TTL is not a great interface for encoders however as its quite susceptible to noise

Yes, I also experienced that very painfully. Unfortunately, the encoders are very cheap. I was able to glue it to RS422 with a TTL converter. In the end it was still cheaper than the good linear encoders.

But for wiring. The SSI interface would like to have 4 cables RX + RX- TX + TX-. How to convert it to CLK, DSN and DO.
CLK = clock
DSN =?
DO = Serial Digital out

TX -> CLK
RX <- DO
DSN = tie active (maybe)