The ABB CT/S2.1 KNX APP-Control Server is a DIN-rail visualization and logic server for KNX installations. It provides web-based commissioning, native apps for iOS, Android, Windows, and macOS, and an integrated webserver — giving end users and integrators a single platform for building control, monitoring, and remote maintenance.

The server connects to the KNX bus via twisted pair and to the local network via Ethernet. It supports KNX IP Secure routing and KNXnet/IP tunneling for remote ETS programming. Third-party integration is built in: a Modbus TCP client and BACnet server, each supporting up to 1000 objects, bridge HVAC, metering, and other building systems into the KNX visualization.

Key Features — Visualization and Logic

User Interface

• Multi-platform apps: Native APP-Control apps for iOS, Android, Windows, and macOS.
• Web-based commissioning: Configure pages, objects, and group addresses through the integrated webserver — no object limit.
• Navigation: List view and room-image layouts for intuitive end-user control.
• End-user scenes: Time programs and scenes creatable directly from the app.

Logic and Integration

• Graphical logic editor: On-device logic without external tools.
• Script editor: LUA scripting for advanced automation and custom functions.
• Modbus TCP client: Up to 1000 objects for third-party device integration.
• BACnet server: Up to 1000 objects for BMS connectivity.
• Remote ETS: KNXnet/IP tunneling for off-site programming and maintenance via APP-Control Connect.
• Energy monitoring: Usage data storage for up to 3 years.

At a Glance

Specification	Detail
Product type	KNX APP-Control Server — visualization and logic
Order code	CT/S2.1 (2CKA006136A0218)
Bus connection	KNX twisted pair (TP)
Network	Ethernet — integrated webserver
Security	KNX IP Secure, encrypted app–device–cloud communication
Integration	Modbus TCP client + BACnet server (1000 objects each)
Apps	iOS, Android, Windows, macOS
Supply voltage	10 … 36 V DC (SELV, external)
Dimensions (W × H × D)	72 × 90 × 65 mm (4 MW)
Weight	234 g
Protection	IP20

Full electrical ratings and classification codes are listed under Technical Specifications. Product manual, installation instructions, APP-Control software, IP Finder, remote ETS guide, CAD, and EPLAN data are under Downloads.

Applications and KNX Integration

• Residential and commercial visualization: Central control for lighting, shading, HVAC, scenes, and alarms from smartphones and tablets.
• Remote maintenance: Service technicians access the installation via APP-Control Connect without on-site visits.
• Cross-protocol BMS: BACnet and Modbus integration for mixed-vendor building management.
• Secure IP backbone: Pair with an IPR/S3.5.1 KNX IP Router Secure for encrypted IP routing and tunneling.
• Power supply: Requires an external SELV supply — typically from an SV/S 30.640.3.1 KNX Power Supply 640 mA auxiliary output or a dedicated 24 V DC supply.
• Wall panels: Complements flush-mounted touch panels such as the ABB RoomTouch 4-inch KNX Control Panel for room-level control alongside the server-based visualization.

Choosing KNX Visualization

The CT/S2.1 is ABB's dedicated APP-Control server for full-featured KNX visualization with logic, scripting, and third-party protocol bridges. For bus infrastructure, combine it with an IPR/S3.1.1 KNX IP Router or the Secure variant, and a suitably sized SV/S 30.320.1.1 or 640 mA power supply depending on line load.