Ethernet 10BASE-T1S: The Game-Changing Single-Pair Network for Automotive and IoT

• 10 min read • IoT & Hardware
Ethernet 10BASE-T1S Automotive IoT Networking Industrial SPE

What is 10BASE-T1S?

10BASE-T1S is a groundbreaking Ethernet physical layer (PHY) standard that fundamentally reimagines how we approach low-speed, short-distance networking. Part of the IEEE 802.3cg standard ratified in 2019, it delivers 10 Mbps Ethernet over a single twisted pair of wires, supporting both point-to-point and multidrop bus topologies without requiring switches.

Unlike traditional Ethernet that typically uses four or eight wires, 10BASE-T1S achieves full-duplex communication over just two wires, making it revolutionary for space-constrained and cost-sensitive applications.

The Technical Foundation

Key Specifications

ParameterSpecificationNotes
Data Rate10 MbpsFull-duplex capable
Cable TypeSingle twisted pairUnshielded or shielded
TopologyPoint-to-point or MultidropUp to 8 nodes on bus
Reach15m (multidrop), 40m (P2P)At maximum data rate
Power DeliveryOptional PoDLUp to 50W (Type 4)
Latency<100 µsDeterministic timing
EMC PerformanceAutomotive GradeCISPR 25 Class 5 compliant

Physical Layer Innovation

10BASE-T1S employs 4B/5B encoding with Differential Manchester Encoding (DME), providing:

  • Clock recovery from data stream
  • DC-balanced transmission
  • Robust noise immunity
  • Self-synchronizing communication

The PHY operates at 25 MHz symbol rate to achieve 10 Mbps throughput after encoding overhead.

PLCA: The Multidrop Enabler

Physical Layer Collision Avoidance (PLCA) is the secret sauce that enables multiple devices to share a single wire pair:

How PLCA Works:

  1. Coordinator Assignment: One node acts as PLCA coordinator
  2. Transmit Opportunities: Each node gets deterministic time slots
  3. Round-Robin Access: Fair, predictable network access
  4. Collision-Free: Eliminates traditional Ethernet collisions
  5. Low Latency: Guaranteed maximum latency based on node count
PLCA Timing Example (8 nodes):
Node 0 (Coordinator): Beacon → TX opportunity
Node 1: Wait → TX opportunity → Pass if no data
Node 2: Wait → TX opportunity → Transmit data
...
Node 7: Wait → TX opportunity → Pass
[Cycle repeats]

Maximum latency = 8 × slot_time = ~64 µs

Comparison with Traditional Ethernet

vs. 10BASE-T (Traditional Ethernet)

Feature10BASE-T10BASE-T1S
Wire Pairs2 pairs (4 wires)1 pair (2 wires)
TopologyStar onlyStar, Bus, or P2P
Minimum CableCAT3Single twisted pair
Switch RequiredYesNo (multidrop)
Cost per NodeHigher40-60% lower
Power over CableSeparate PoEIntegrated PoDL

vs. 100BASE-T1 (Automotive Ethernet)

Feature100BASE-T110BASE-T1S
Speed100 Mbps10 Mbps
TopologyPoint-to-point onlyP2P + Multidrop
Use CaseCameras, infotainmentSensors, actuators
ComplexityHigher PHY costSimpler, lower cost
Power Consumption100-200 mW50-100 mW

vs. CAN Bus

FeatureCAN Bus10BASE-T1S
Data Rate1 Mbps max10 Mbps
Protocol OverheadHighStandard Ethernet
Software StackSpecializedStandard TCP/IP
DiagnosticsLimitedFull Ethernet tools
Future-ProofingLegacyModern, evolving

Automotive Applications

The Zonal Architecture Revolution

Modern product are transitioning from domain-based to zonal architectures, where 10BASE-T1S plays a crucial role:

Traditional Domain Architecture:
ECU ← CAN → ECU ← CAN → ECU
ECU ← LIN → ECU ← LIN → ECU
Camera ← LVDS → Processing Unit

Zonal Architecture with 10BASE-T1S:
Zone Controller ← 10BASE-T1S Bus → [Sensor1, Sensor2, Actuator1, Actuator2]
      ↓
   100BASE-T1 or 1000BASE-T1
      ↓
Central Compute Unit

Specific Automotive Use Cases

1. Sensor Networks

  • Ultrasonic parking sensors: 8 sensors on single wire pair
  • Temperature monitoring: Engine, cabin, battery sensors
  • Pressure sensors: Tire pressure, fuel system, brake system
  • Rain/light sensors: Simplified wiring harness

2. Actuator Control

  • Door modules: Locks, mirrors, windows on shared bus
  • Seat control: Motors, heaters, position sensors
  • HVAC actuators: Dampers, fans, blend doors
  • Lighting control: LED modules with diagnostic feedback

3. Battery Management Systems (BMS)

  • Cell monitoring: Daisy-chain topology for cell voltage/temperature
  • Isolated communication: Simplified galvanic isolation
  • Reduced wiring: 70% weight reduction vs traditional BMS wiring

Weight and Cost Reduction

Case Study: Mid-size Vehicle

  • Traditional wiring harness: 40-60 kg, 2-3 km of cables
  • With 10BASE-T1S adoption: 30% weight reduction possible
  • Cost savings: $50-100 per vehicle in wiring alone
  • Assembly time: 20% reduction in harness complexity

Industrial IoT Applications

Factory Automation

10BASE-T1S enables new architectures for industrial control:

Edge Sensor Networks

PLC/Edge Controller
    ↓ (10BASE-T1S Multidrop)
[Temp] [Humidity] [Vibration] [Pressure] [Flow]
  ↓        ↓          ↓           ↓        ↓
Real-time data with <100µs latency

Advantages:

  • Simplified installation: Single cable run for multiple sensors
  • Real-time capability: Deterministic PLCA scheduling
  • Standard protocols: MQTT, OPC UA over Ethernet
  • Remote configuration: IP-addressable sensors

Building Automation

Smart Lighting Systems

  • Individual LED fixture control and monitoring
  • Occupancy sensors on shared bus
  • Daylight harvesting sensors
  • Emergency lighting status

HVAC Control

Zone Controller ← 10BASE-T1S → [VAV Box] [Thermostat] [CO2 Sensor] [Damper]
  • Reduced installation cost: 40% vs traditional systems
  • IP-based commissioning and diagnostics
  • Energy monitoring per zone

Agricultural IoT

Precision Agriculture

  • Soil monitoring network: pH, moisture, nutrient sensors
  • Irrigation control: Valve actuators on shared bus
  • Weather stations: Multiple sensors, single cable
  • Greenhouse automation: Temperature, humidity, light control

Implementation Example:

Field Gateway (Solar Powered)
    ↓ 10BASE-T1S Bus (40m reach)
[Soil-1] [Soil-2] [Valve-1] [Valve-2] [Weather]
    ↑                            ↑
Power over Data Line (PoDL) - 500mW per sensor

Power over Data Line (PoDL)

PoDL Classes for 10BASE-T1S

ClassVoltageCurrentPower at PDApplications
1012V92mA1.0WSimple sensors
1112V240mA2.5WSmart sensors
1224V120mA2.5WIndustrial sensors
1324V250mA5.0WActuators, cameras
1448V229mA10WHigh-power devices
1548V632mA30WMotor controllers

PoDL Architecture

PSE (Power Sourcing Equipment)
    ↓
Coupling Network (Inductors + Capacitors)
    ↓
Single Twisted Pair (Data + Power)
    ↓
Decoupling Network
    ↓
PD (Powered Device) + PHY

Design Considerations

  1. Inrush Current Management: Soft-start circuits required
  2. Fault Protection: Overcurrent, short circuit, thermal
  3. EMI/EMC: Proper filtering for automotive/industrial
  4. Cable Resistance: Voltage drop calculations critical

Implementation Considerations

Cable Selection

For Automotive

  • Unshielded: Cost-optimized for short runs (<5m)
  • Shielded: EMC-critical applications
  • Cable specs: 100Ω ±10%, <65 dB/km attenuation at 12.5 MHz

For Industrial

  • Industrial Ethernet Cable: Cat 5e performance sufficient
  • Flex-rated: For moving applications
  • Oil-resistant: For harsh environments

Network Design Best Practices

1. Topology Planning

Multidrop Bus Design Rules:
- Maximum 8 nodes (including coordinator)
- Total cable length ≤15m
- Stub length ≤0.3m
- Termination: 100Ω at each end

2. PLCA Configuration

  • Assign node IDs sequentially
  • Coordinator at physical bus center if possible
  • Configure transmit opportunity timer based on traffic patterns

3. Timing Analysis

Worst-case latency = N × (TO_TIMER + COMMIT_TIME)
Where:
- N = number of nodes
- TO_TIMER = transmit opportunity window (typ. 24 bit times)
- COMMIT_TIME = time to commit transmission (typ. 4 bit times)

For 8 nodes: ~22.4 µs worst-case

EMC and Signal Integrity

Automotive EMC Requirements

  • Conducted emissions: CISPR 25 Class 5
  • Radiated emissions: <37 dBµV/m (30-230 MHz)
  • BCI immunity: 100mA (1-400 MHz)
  • ESD: ±8kV contact, ±15kV air

PCB Design Guidelines

  1. Differential routing: Maintain 100Ω impedance
  2. Length matching: <5mm difference
  3. Via minimization: Use for layer transitions only
  4. Ground plane: Solid reference required
  5. Connector placement: Away from high-speed signals

Available Silicon and Development Tools

PHY Transceivers

Production Silicon

  1. NXP TJA1101B: Automotive qualified, AEC-Q100
  2. Microchip LAN8670: Industrial temperature range
  3. Broadcom BCM89810: Integrated diagnostics
  4. Marvell 88Q2112: Low power consumption

Key Features Comparison

VendorPartPLCAPoDLPackageCost
NXPTJA1101BYesExternalQFN-32$2-3
MicrochipLAN8670YesClass 10-11QFN-24$1.5-2.5
BroadcomBCM89810YesExternalQFN-32$2.5-3.5

Development Boards

  1. EVB-LAN8670: Microchip evaluation board

    • USB to 10BASE-T1S bridge
    • PoDL support
    • PLCA configuration software

  2. NXP FRDM-10BASE-T1S: Freedom development platform

    • Multiple PHYs for bus testing
    • Arduino compatible headers
    • Integrated debugger

  3. Custom Arduino Shield: Open-source designs available

    • Simple SPI interface
    • Cost: <$50 to build

Software Support

Linux Drivers

# Mainline kernel support (5.12+)
modprobe lan867x
ip link set eth0 up
ethtool -s eth0 plca-enable on plca-node-id 1

# PLCA status monitoring
ethtool -I eth0 --show-plca-status

Embedded Libraries

  • lwIP: Lightweight TCP/IP stack support
  • FreeRTOS+TCP: Integrated PHY drivers
  • Zephyr OS: Native 10BASE-T1S support

Real-World Deployment Examples

Case Study 1: Electric Vehicle Battery Pack

Challenge: Monitor 96 battery cells with temperature and voltage

Traditional Solution:

  • Daisy-chained analog monitoring ICs
  • Complex isolation requirements
  • Limited diagnostic capability

10BASE-T1S Solution:

BMS Controller
    ↓ 10BASE-T1S (isolated)
[Module 1: 12 cells] → [Module 2: 12 cells] → ... → [Module 8: 12 cells]

Benefits:
- Standard Ethernet diagnostics
- Firmware updates over network
- 60% reduction in wiring weight
- Real-time cell balancing coordination

Case Study 2: Smart Building Retrofit

Challenge: Add IoT sensors to existing building without new wiring

Solution Architecture:

Existing Ethernet Drop
    ↓
10BASE-T1S Gateway
    ↓ Single cable run (40m)
[Temp] [CO2] [Occupancy] [Light] [Sound]

Implementation:
- Used existing conduit space
- PoDL powers all sensors (500mW each)
- Cloud connectivity via gateway
- Installation time: 2 hours vs 2 days traditional

Case Study 3: Agricultural Greenhouse

Challenge: Monitor and control 200m² greenhouse environment

10BASE-T1S Network Design:

Central Controller
    ├─ Bus 1: Environmental sensors (15m)
    ├─ Bus 2: Irrigation valves (15m)
    ├─ Bus 3: Vent actuators (10m)
    └─ Bus 4: Grow lights control (12m)

Results:
- 70% reduction in installation cost
- Remote management capability
- Energy usage optimization: 25% savings
- Predictive maintenance alerts

Future Developments

Standards Evolution

IEEE 802.3da (10BASE-T1L)

  • Long-reach variant: up to 1000m
  • Process automation focus
  • Intrinsically safe options

Enhanced PLCA

  • PLCA 2.0: Under development
  • Support for 16+ nodes
  • Dynamic bandwidth allocation
  • QoS mechanisms

Emerging Applications

1. Autonomous Vehicles

  • Sensor fusion networks
  • Redundant safety systems
  • V2X communication gateways

2. Smart Cities

  • Street lighting control
  • Traffic sensor networks
  • Environmental monitoring
  • Parking management systems

3. Wearable Networks

  • Body area networks
  • Medical device connectivity
  • Sports performance monitoring

4. Robotics

  • Distributed motor control
  • Sensor integration
  • Collaborative robot communication

Technology Roadmap

2024-2025:

  • Second-generation PHYs with lower power
  • Integrated MCU+PHY solutions
  • Standardized connectors for industrial

2025-2027:

  • 25BASE-T1S for higher bandwidth
  • Time-sensitive networking (TSN) support
  • Wireless gateway integration

2027+:

  • Plastic optical fiber variants
  • Integrated security features
  • AI-driven network optimization

Design Example: IoT Sensor Node

Hardware Architecture

MCU (STM32/ESP32/etc)
    ↓ SPI
10BASE-T1S PHY
    ↓ MDI
Transformer + ESD Protection
    ↓
RJ11/Phoenix Connector

Bill of Materials (Estimated)

ComponentPartQuantityCost
MCUSTM32G01$2.00
PHYLAN86701$2.00
TransformerHX1188NL1$0.80
ESD ProtectionTPD2E2U061$0.30
ConnectorRJ111$0.50
PassivesVarious20$0.40
Total$6.00

Firmware Skeleton

// 10BASE-T1S initialization
void eth_init(void) {
    // Reset PHY
    phy_write(REG_RESET, 0x8000);

    // Configure PLCA
    phy_write(REG_PLCA_CTRL, PLCA_ENABLE | NODE_ID_2);
    phy_write(REG_PLCA_BURST, BURST_DISABLE);

    // Set transmit opportunity timer
    phy_write(REG_TO_TIMER, 0x18); // 24 bit times

    // Enable auto-negotiation
    phy_write(REG_AN_CTRL, AN_ENABLE);

    // Initialize MAC
    mac_init();
}

// Packet transmission with PLCA
void eth_send(uint8_t *data, uint16_t len) {
    // Wait for transmit opportunity
    while(!(phy_read(REG_PLCA_STATUS) & TX_OPPORTUNITY));

    // Send packet
    mac_send_frame(data, len);
}

Troubleshooting Guide

Common Issues and Solutions

  • Check cable continuity and termination (100Ω)
  • Verify PLCA coordinator presence
  • Ensure unique node IDs
  • Check power supply stability

2. High Packet Loss

  • Reduce cable length (<15m multidrop)
  • Improve grounding and shielding
  • Check for impedance mismatches
  • Verify stub length (<30cm)

3. PLCA Synchronization Loss

  • Ensure single coordinator on bus
  • Check for EMI interference
  • Verify PHY clock accuracy (±100ppm)
  • Update PHY firmware if available

4. PoDL Issues

  • Calculate voltage drop for cable length
  • Check current limit settings
  • Verify PSE classification
  • Ensure proper decoupling networks

Conclusion

10BASE-T1S represents a paradigm shift in how we approach edge connectivity. By bringing true Ethernet to the simplest sensors and actuators over just two wires, it enables:

  • Unprecedented simplicity: Single pair, multiple devices
  • Cost reduction: 40-60% lower than traditional Ethernet
  • Weight savings: Critical for automotive and aerospace
  • Future-proof: Standard IP networking to the edge
  • Deterministic: Guaranteed latency with PLCA

For IoT and automotive developers, 10BASE-T1S offers a compelling alternative to legacy fieldbuses and proprietary protocols. Its combination of simplicity, cost-effectiveness, and standard Ethernet compatibility positions it as a foundational technology for the next generation of connected devices.

As the ecosystem matures with more silicon options, development tools, and real-world deployments, 10BASE-T1S is poised to become the de facto standard for short-distance, multi-drop networking in automotive, industrial, and IoT applications.

The transition from specialized industrial protocols to standard Ethernet at every level – from the cloud to the simplest sensor – is no longer a distant vision but an achievable reality with 10BASE-T1S.

Resources and Further Reading

Standards Documents

Technical Resources

Development Tools

Industry Organizations

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