EsoCoreEsoCore

Industrial Fieldbus Protocols

This page outlines the practical aspects of supporting Modbus, PROFIBUS and PROFINET on EsoCore hardware and firmware. It focuses on physical interfaces, topology, addressing, timing, EMC, and certification considerations so designs are robust in industrial environments.

Modbus RTU (RS‑485)

Physical Layer

  • RS‑485 half‑duplex, differential pair A/B plus reference GND
  • Isolated transceiver recommended for ESD/EMC and ground potential differences
  • 3‑pin terminal block (A/B/G) with shield termination near chassis
  • Switchable 120 Ω termination + optional biasing (pull‑up/pull‑down)

Topology & Cabling

  • Linear bus (daisy chain), avoid stubs
  • Cable: twisted pair, 120 Ω characteristic impedance
  • Max nodes: 32 per segment without repeaters (more with modern transceivers)

Addressing & Framing

  • Node addressing: 1–247 (DIP switch or software configurable)
  • 8‑E‑1 or 8‑N‑2 common, CRC‑16 integrity

Timing & Throughput

  • Typical 9600–115200 bps (up to 1 Mbps in some systems)
  • Silent interval between frames (3.5 character times) must be enforced

Firmware Notes

  • UART with DMA + precise inter‑frame timing
  • CRC‑16 table or hardware accelerator

BOM & Connectors

  • Isolated RS‑485 transceiver
  • 3‑pin 5.08 mm terminal block
  • DIP switch for address and termination enable

Modbus TCP (Ethernet)

Physical Layer

  • Standard 10/100 Ethernet (existing RJ45 + PHY)

Topology & Addressing

  • IP addressing via DHCP or static
  • TCP port 502

Firmware Notes

  • Lightweight TCP stack with Modbus application server
  • Same function codes as RTU with PDU carried over TCP

PROFIBUS DP

Physical Layer

  • RS‑485 with PROFIBUS electrical levels
  • DB‑9 male with shield and integrated chassis connection
  • Termination selectable via switch at both ends of the segment

Topology & Performance

  • Linear bus with repeaters for large networks
  • 9.6 kbps to 12 Mbps, timing tighter than generic RS‑485

Addressing & Configuration

  • Node address 0–126, usually via rotary/DIP switch or software tool
  • GSD file describes device to the PLC/engineering tool

Firmware Notes

  • Real‑time deterministic stack required for high baud rates
  • State machine: parameterization → configuration → data exchange

BOM & Connectors

  • PROFIBUS‑compliant RS‑485 transceiver
  • DB‑9 male with shield
  • DIP switch for address/termination

PROFINET (Device)

Physical Layer & Topology

  • Standard Ethernet (RJ45 with magnetics)
  • Star or line topology via switches; device may be single‑port

Real‑Time Classes

  • RT (Real Time): cyclic I/O over VLAN‑tagged frames
  • IRT (Isochronous Real Time): tighter jitter with special switch silicon (future option)

Addressing & Discovery

  • IP via DCP set name/IP, discovery with LLDP
  • GSDML file describes device to engineering tools

Firmware Notes

  • Prioritized traffic, bounded cycle times (2–4 ms typical for RT)
  • Alarms, diagnostics, records; SNMP/LLDP for topology

BOM & Connectors

  • Existing Ethernet PHY and MagJack
  • Optional 2‑port switch (future revision) for line topology devices

EMC, Safety and Certification

  • Cable shield bonding at the connector to chassis ground
  • ESD arrays on data lines; common‑mode chokes for USB/Ethernet where needed
  • Creepage/clearance and isolation for RS‑485 and power domains
  • Follow conformance test plans: Modbus interoperability tests, PROFIBUS (PIT), PROFINET (PNO) certification

References

  • See the Hardware Requirements for mechanical and connector details
  • See the BOM for specific transceivers, connectors, and switches