0
\$\begingroup\$

enter image description here

I'm trying to interface a rotary encoder (IFM RM8002) with an Arduino Nano. The encoder uses the SSI protocol with RS-422 signaling. It has a 2-meter cable, no big stretch for RS-422.

I have a TTL / RS-422 module (amazon.com/gp/B07BJJ6C88) to provide the necessary level translation. It's powered by +5, same as the encoder. From what I've gathered, this is a plain-Jane SSI interface encoder and a commodity level translator.

I'm sending the specified clock signal, at 500KHz, in the correct polarity, but the encoder does not respond (its data lines never change). I've tried rates from 125KHz to 1MHz with no joy.

The scoped clock signals on the Y/Z pins are ~2.7V p-p. The spec I found for RS-422 levels seems to say that would be OK.

I don't know if this is a clue, but the A/B data lines from the encoder are both idling at 0V. Since this is RS-422, should they be at two different levels when idle? The encoder is definitely powered.

Is there some secret SSI sauce here that I might be missing? I have a call in to IFM tech support but they don't guarantee a quick response.

\$\endgroup\$
13
  • \$\begingroup\$ please add a schematic diagram of the circuit \$\endgroup\$
    – jsotola
    Commented Sep 20 at 0:00
  • \$\begingroup\$ Kinda hard to say. Usually it's not done with a uart. It's only a physical rs422 layer. You need something that does ssi - a microcontroller or an fpga. Or a servo drive. \$\endgroup\$
    – TQQQ
    Commented Sep 20 at 0:11
  • \$\begingroup\$ @jsotola - added diagram \$\endgroup\$
    – Jim Mack
    Commented Sep 20 at 3:00
  • \$\begingroup\$ @TQQQ - sorry, I don't get what you're saying. Does the diagram help? \$\endgroup\$
    – Jim Mack
    Commented Sep 20 at 3:01
  • 1
    \$\begingroup\$ maybe the encoder is being held in a reset state \$\endgroup\$
    – jsotola
    Commented Sep 20 at 3:11

1 Answer 1

Reset to default
0
\$\begingroup\$

It turns out that while the encoder was getting power, there was enough loss in the USB cable powering the Nano that the voltage was just below the minimum 4.5V needed. The nominal +5v was actually 4.3V. Once that was corrected, everything works as designed.

Sorry for the distraction

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.