A servo drive is only as good as its feedback. The encoder reports rotor position for commutation, velocity for damping, and absolute position for precision moves. Choose the interface that matches your drive electronics, your dynamic requirements and your supply strategy.
What a servo encoder must deliver
- Absolute position at power-up — no homing, no lost-position after a restart.
- High resolution — 17-bit (131,072 steps/turn) is a strong baseline for modern servos.
- Low latency — position updates must keep pace with high-bandwidth current loops.
- Integrity — safety and high-dynamic applications need error detection (CRC).
- Reliability — the encoder must survive years of thermal cycling and vibration.
The three interfaces that matter
| Criterion | RS485 (Tamagawa) | BISS-C | SSI |
|---|---|---|---|
| Direction | Bidirectional | Bidirectional | Clock/data out |
| Data integrity | Protocol-defined | CRC on every frame | Optional parity |
| Speed | Medium | Highest | Low-medium |
| Ecosystem fit | Widest for servos | Modern high-dynamic drives | PLCs and general control |
| Drop-in replacement | Yes — Tamagawa compatible | Yes — pin-compatible wiring | Yes |
RS485 and the Tamagawa protocol
Tamagawa-compatible RS485 absolute encoders became the de facto standard across Asian servo ecosystems. If your drive speaks it, an RS485 encoder is the fastest path to qualification — same wiring, same data format. This makes the RM10 rotary encoder a drop-in candidate for replacement programs.
BISS-C for high-dynamic drives
BISS-C is the open, fast, CRC-protected protocol favored by robot and high-performance servo designers. It offers sub-microsecond position latencies with integrity checking — exactly what modern drive ASICs expect. If you are designing a new drive or robot joint, BISS-C gives you headroom.
SSI for simplicity
SSI is the universal serial interface understood by nearly every PLC and motion controller. It is slower and one-directional, but it is simple, proven and cost-effective for general industrial axes.
One encoder family, all three protocols
The RM series carries RS485 (Tamagawa), BISS-C and SSI on a single 8-pin terminal definition. That means one qualified encoder can serve multiple machine lines — and a future protocol change doesn't force a cable redesign. For drive makers, this simplifies inventory and second-sourcing.
Practical integration tips
- Match the protocol to the drive you have — or the drive you plan to build.
- Verify the absolute position format (single-turn vs multi-turn) before ordering.
- Ask for sample evaluation boards and protocol documentation during qualification.
- Check ESD and vibration ratings — drives live in electrically noisy cabinets.