AIO-422-R1 Analog I/O & RTD

Tech Specs

Installation, Environmental & Mechanical

Home Assistant / Modbus / Web Config Integration

The AIO-422-R1 supports flexible integration with:

• HomeMaster MicroPLC / MiniPLC controllers as Modbus RTU masters
• PLC and SCADA systems via RS-485 Modbus RTU
• Home Assistant via ESPHome on the controller (entities from Modbus registers)
• Direct USB-C configuration using browser-based WebConfig

Configuration is saved persistently and restored at power-up.

Quick Setup Process (USB-C WebConfig)

1. Mount & Power — mount on DIN rail and connect 24 V DC.
2. Connect USB-C — attach USB-C to your PC.
3. Open WebConfig — open the WebConfig page in Chrome or Edge.
4. Connect Device — click Connect and select the serial device.
5. Configure Modbus — set address and baud rate.
6. Configure I/O behavior — analog input scaling, analog output setpoints, RTD wiring mode (2/3/4-wire).
7. Save & Disconnect — save settings and disconnect USB-C.

Register-level and entity mapping details are available in the AIO-422-R1 README.

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200
  parity: NONE
  stop_bits: 1

modbus:
  id: modbus_bus
  uart_id: uart_modbus

packages:
  aio1:
    url: https://github.com/isystemsautomation/HOMEMASTER
    ref: main
    files:
      - path: AIO-422-R1/Firmware/default_aio_422_r1_plc/default_aio_422_r1_plc.yaml
        vars:
          aio_prefix: "AIO#1" # shown in Home Assistant entity names
          aio_id: aio_1      # internal unique id
          aio_address: 3     # Modbus address set in WebConfig
    refresh: 1d

Cabling and Wirings

24 V DC Supply (V+ / 0V)

Connect + to V+ and − to 0V.

• Use a regulated 24 V DC SELV supply
• Apply upstream fuse protection according to cabinet rules
• Keep power wiring separated from low-level analog/RTD cabling

Analog Inputs (AI1–AI4, 0–10 V)

AI channels expect 0–10 V signals and use AGND as analog ground.

Analog Outputs (AO1–AO2, 0–10 V)

Outputs provide 0–10 V (DAC MCP4725). Keep load current within recommended limits (max 10 mA per channel).

RTD Inputs (RTD1 / RTD2, PT100/PT1000)

Supports 2-, 3-, or 4-wire RTD wiring. Shielded RTD cables improve accuracy and fault detection stability.

RS-485 Modbus (A / B / COM)

Wire A to A, B to B, and COM to your RS-485 reference as required.

Cable Recommendations & Shield Grounding

General routing rules

• Route low-level signal cables (analog and RTD) separately from power and high-current conductors
• If crossing power cables is unavoidable, cross at 90°
• Keep cable runs as short as practical and avoid parallel runs with high-current wiring
• Label cables and provide strain relief at terminals

Analog (0–10 V) cable

• Use twisted pair (Signal + AGND) per analog channel
• Use overall shielding for typical installs, or individually shielded pairs for high-EMI environments
• Examples: J-Y(ST)Y (overall shield) or LI2YCY PiMF (shielded twisted pairs)

RTD temperature cable

• Recommended: shielded cable for RTD (PT100/PT1000), using 2/3/4-wire wiring as required
• Shielded pairs are recommended for best accuracy (especially for 4-wire)
• Example: J-Y(ST)Y (overall shield) or LI2YCY PiMF (pairs)

RS-485 (Modbus) cable

• Use twisted pair for A/B (characteristic impedance 120 Ω recommended)
• Prefer shielded cable in industrial/noisy panels
• Use an additional conductor/pair as COM reference if required by the RS-485 network design

Shield grounding

• Bond cable shield(s) to cabinet PE/EMC ground at the PLC/controller end only by default
• Do not connect shields directly to signal terminals (A/B/COM)

System Architecture & Pinout

System block diagram showing MCU, analog/RTD front-end, and RS-485 interfaces.

MCU GPIO and connector/pin reference (check revision notes in the datasheet).

Field board: analog inputs/outputs and RTD wiring interface.

MCU board: RS-485 transceiver, USB-C interface, and power conversion stages.

Safety and Installation Notes

• SELV circuits: the power input and signal terminals are SELV circuits; install only in an appropriate control cabinet
• Qualified personnel only: installation by trained technicians familiar with analog wiring and industrial control safety
• Protect all module wiring terminals against accidental contact using the required front plate/door
• Do not expose the module to outdoor conditions; the enclosure is IP20 (inside cabinet only)
• Use the recommended cable types (twisted/shielded) to reduce noise and improve analog/RTD accuracy
• Keep analog/RTD cables separated from power and high-current wiring to avoid interference

Compliance & Certifications

The HomeMaster AIO-422-R1 is CE marked and designed to comply with applicable European Union directives. The manufacturer maintains technical documentation and a signed EU Declaration of Conformity (DoC).

EU Directives

EMC 2014/30/EU · LVD 2014/35/EU · RoHS 2011/65/EU

Harmonised Standards

Safety Notice

The power input and signal terminals are SELV circuits. Relay/contact output circuits are not part of this module.