Modbus RTU remote terminal unit C4

LTE Cat 1EthernetRS-485

Overview
RESI supplies an industrial IoT controller based on the Raspberry Pi® Compute Module 4. The device combines the standard interfaces of the Compute Module 4 with industrial-grade electronics and an additional ARM® coprocessor to reliably manage time-critical IO functions.

What is different?
The Compute Module 4 board is integrated into an industrial enclosure for DIN-rail and wall mounting. Available enclosure sizes: 4MU, 8MU and 12MU. Fits standard control cabinets with a 45 mm cutout. A wide-range internal power supply (12–48 VDC) is included.

Coprocessor / Hardware features
The integrated ARM® coprocessor handles the serial RS485 interface and time-critical tasks. Features include a unique 96-bit serial number, 2 kB ferromagnetic RAM for persistent values, a real-time clock with backup capacitor, status LEDs and DIP switches for software use.

Standard functions of the Compute Module 4

• 1 × Micro HDMI
• 1 × Ethernet
• 2 × USB 2.0
• RAM options: 2 GB, 4 GB or 8 GB
• 32 GB SD card with Linux OS (preinstalled)

Built-in inputs and outputs (IO)
Various versions include integrated IO. The ARM® coprocessor aggregates all IO internally so the application software needs only a single serial interface. Communication interfaces (depending on configuration):

• /dev/ttyACM0: ASCII text protocol
• /dev/ttyACM1: MODBUS/RTU master
• /dev/ttyACM2: RS485 via USB (native serial in Linux; direction switching handled by the coprocessor)

IO variants / examples

• Versions with digital inputs: e.g. 14 or 48 digital inputs for 12–250 Vac/dc signals
• Low-voltage digital input versions: e.g. 6 to 152 digital inputs for 12–48 Vdc signals
• Versions with relay outputs
• Special IOs: LED strip drivers, temperature sensor inputs, blind/shade control

Universal analog inputs/outputs (AIOX)
Available with 4 / 8 / 16 channels. Each channel can be individually configured as:

• Analog input: 0/2–10 V or 0/4–20 mA
• Analog output: 0/2–10 V or 0/4–20 mA
• Resistance measurement input: 0 … 1 MΩ
• PT100, PT1000, NI1000 (DIN43760) sensor input
• Digital input: 24 V DC or dry contact

Extensions / Options
Available add-ons include:

• Second Ethernet port
• Integrated LTE modem

Software and use cases
Supplied with a standard Raspberry Pi Linux distribution; compatible with many open-source solutions and development environments. Examples:

• Node-RED, NodeJs, Python, Java, JavaScript, HTML, C#, C++, Scratch
• Databases: MariaDB, MongoDB, InfluxDB, PostgreSQL
• Visualization / Web server: Grafana, Apache
• Home automation: OpenHAB, FHEM, Home Assistant, ioBroker
• Cloud / protocols: MQTT, HTTPS, Azure IoT, AWS web services
• VPNs / routers: OpenWrt, OpenRouter, OpenVPN, WireGuard
• Multimedia: KODI
• Industrial PLC: CODESYS

Note on versions
Not all combinations are technically possible. Please check the order number / item details to ensure the desired configuration.

Technical specifications

• Product name: C4 (C4-nur DEs variant)
• Article no.: RESI-C4-A-6DI-2GB
• Enclosure: Industrial enclosure for DIN-rail / wall mounting (4MU / 8MU / 12MU)
• Power supply: Wide-range 12–48 VDC (internal)
• Compute Module interfaces: 1× Micro HDMI, 1× Ethernet, 2× USB 2.0
• RAM: 2 GB / 4 GB / 8 GB (configurable)
• Storage: 32 GB SD card with Linux
• Coprocessor: ARM® coprocessor with 96-bit serial, 2 kB ferromagnetic RAM, RTC with backup capacitor, status LEDs, DIP switches
• Serial interface mapping: /dev/ttyACM0 (ASCII), /dev/ttyACM1 (MODBUS/RTU master), /dev/ttyACM2 (RS485)
• Analog IO (AIOX): 4/8/16 channels, configurable (0/2–10 V, 0/4–20 mA, resistance, PT100/PT1000/NI1000)
• Digital IO: Variants with different channel counts (e.g. 6, 14, 48, 64, 128, 152)
• Options: 2nd Ethernet, integrated LTE modem
• Price (net, standard configuration shown): 309.10 EUR