EtherMUX Protocol Documentation
Acronyms
- MD: Main Device (Master)
- SD: Secondary Device (Slave)
- SPE: Single Pair Ethernet
Overview
EtherMUX is an open-source, ultra-low latency, point-to-multipoint communication protocol. It simplifies system wiring by multiplexing signals onto a single pair of wires.
- Supports up to 64 general-purpose signals and 254 virtual COM ports
- Establishes a full-duplex virtual communication channel from the MD to all SD devices over a single twisted pair SPE cable
- Devices are connected in a daisy chain configuration (no switch is required)
Target Applications
Designed for multi-axis machine control such as:
- 🖨️ 3D printers
- 🤖 Robotic arms
These systems require synchronous motor control with minimal delay and skew. EtherMUX ensures:
- Time synchronization between MD and SD devices
- Reliable transfer of Step and Direction pulses for stepper motors and servos
- Reduced frame overhead by removing traditional Ethernet headers (except for Frame Check Sequence (FCS))
Ultra-Low Latency
Traditional Ethernet uses a store-and-forward approach, introducing latency as packets are assembled and routed through switches. EtherMUX avoids this by:
- Using cut-through forwarding
- Eliminating unnecessary headers
- Maintaining tight timing for motion-critical applications
PHY Interfaces
EtherChain supports the following Single Pair Ethernet (SPE) PHYs:
| Interface |
Max Chain Length |
| 100BaseT1 Full Duplex |
15 meters |
- Based on daisy chain cut-through data flow
- Data is looped back at the end of the chain
Serial over EtherMUX
While I²C is common for sensors and peripherals, its limited range and turnaround time make it unsuitable for long-distance or time-critical reads. EtherChain offers a more robust alternative.
EtherMUX vs Ethernet
| Feature |
Standard Ethernet |
EtherMUX |
| Topology |
Star (point-to-point) |
Daisy chain |
| Switch Requirement |
Requires switch/router |
No switch required |
| Device Communication |
Peer-to-peer possible |
Only MD-to-SD and SD to MD communication |
EtherMUX vs EtherCAT
EtherChain shares EtherCAT’s low-latency philosophy but avoids its complexity:
- No backward compatibility burden
- Lightweight and easy to implement
- Does not support 3-port branching devices
Single Pair Ethernet (SPE) Integration
EtherMUX optimizes SPE by:
- Removing Ethernet headers to save bandwidth and reduce latency
- Eliminating MAC addresses (All packets are broadcast to all nodes)
- Using a bridge protocol on the MD to interface with standard Ethernet networks
Time Synchronization
EtherMUX supports a Distributed Clock mechanism to synchronize all SD devices with the MD’s master clock, ensuring precise timing across the network.
Philosophy
EtherMUX is driven by a commitment to low cost and simplicity:
- Minimizes component cost, CPU load, power consumption, and system complexity
- Reduces labor costs by keeping the system understandable and maintainable
- Prioritizes simplicity over feature creep to avoid escalating system costs