# Beckhoff CX8091

Hardware · `CX8091` · verification: source checked

The Beckhoff CX8091 is a control system with a switched Ethernet port and a bus interface for E-bus or K-bus terminals. It automatically recognizes the connected I/O system during start-up and is programmed with TwinCAT 2 through the fieldbus interface or the additional Ethernet interface. It supports BACnet or OPC UA, with simultaneous use not recommended due to the small memory.

## Specification

| Property | Value |
|---|---|
| Category | plc |
| Weight | 0.18 kg |
| Ethernet ports | 3 |
| Processor | Arm9™, 400 MHz |
| Supply voltage | 24 V DC (-15%/+20%) |
| Power consumption | 0.003 kW |
| IP rating | IP20 |
| Operating temp min | 0 °C |
| Operating temp max | 55 °C |

## Connected

- Manufacturer: [Beckhoff Automation](https://machineschema.com/manufacturer/beckhoff.md)
- Protocols: [OPC UA](https://machineschema.com/protocol/opc-ua.md)

## Safety

- Approvals/markings: CE, UL, ATEX, IECEx, cFMus.
- ATEX marking: II 3G Ex nA IIC T4 Gc; II 3D Ex tc IIIC T135°C Dc.
- IECEx marking: Ex nA IIC T4 Gc; Ex tc IIIC T135°C Dc.
- cFMus marking: Class I, Division 2, Groups A, B, C, D; Class I, Zone 2, AEx ec IIC T4 Gc.
- Windows Embedded CE 6 extended support has ended; up-to-date security updates can no longer be provided.

## Study notes

- Product status: regular delivery, not recommended for new projects; recommended alternative is CX8290.
- BACnet is supported as an alternative protocol to OPC UA; simultaneous use is not recommended due to the small memory.
- I/O connection accepts E-bus or K-bus terminals and automatically recognizes the connected I/O system during start-up.
- Programming languages: IEC 61131-3; control software: TwinCAT 2 PLC.
- Main memory: 64 MB DDR2 RAM, not expandable. Flash memory: microSD slot with 512 MB card included, optionally expandable.
- Integrated 1-second UPS with 1 MB on microSD card.
- Interfaces: 1 x RJ45 10/100 Mbit/s, 1 x USB device behind the front flap, 1 x bus interface; the bus interface has 2 x RJ45 switched at 100 Mbit/s.
- Cooling is passive; diagnostics LEDs are 1 x TC status, 1 x WD and 1 x error.
- Internal battery-backed clock for time and date; battery behind the front flap and exchangeable.
- Current supply for E-bus/K-bus: 2 A. Max power consumption for E-bus/K-bus: 10 W (5 V/max. 2 A).
- Dimensions: 64 mm x 100 mm x 73 mm. Relative humidity: 95%, no condensation. Storage temperature: -25…+85°C.
- Vibration/shock resistance conforms to EN 60068-2-6/EN 60068-2-27; EMC immunity/emission conforms to EN 61000-6-2/EN 61000-6-4.

## Sources

1. [Embedded PC with Arm9™ and BACnet/IP or OPC UA](https://www.beckhoff.com/en-en/products/ipc/embedded-pcs/cx8000-arm9/cx8091.html) (accessed 2026-10-25)

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