One. Overview of RDM protocol

• RDM is a two-way communication protocol based on DMX512 protocol, which is designed for remote management of intelligent equipment such as stage lighting and performing arts equipment. On the basis of retaining the DMX512 physical layer, it adds two-way data communication capabilities, allowing parameters configuration, condition monitoring and fault diagnosis between the controller (such as the dimmer table) and the luminaire.

Two, RDM protocol core features

Bidirectional communication

• Based on the unidirectional transmission of DMX512, RDM realizes bidirectional communication between the controller and the device through half-duplex mode.
• The response mechanism is adopted: the controller sends query commands and the device returns response data.

Plug-and-Play

• Automatic device Discovery is supported, and the controller can dynamically identify RDM devices connected in the network.
• Each device has a unique UID (16 bytes, including the manufacturer ID and device serial number).

Data compatibility

• Shares the same physical link with DMX512 (RS-485 interface), compatible with existing DMX cables and architectures.
• RDM data packets are inserted into the DMX512's ** "Packet Interval" ** to avoid interference with normal DMX signals.

Standardized parameter management

• Define a uniform parameter ID (PID) for controlling device functions (such as brightness, color temperature, fault status, etc.).
• Support for custom manufacturer extension parameters.

Three.RDM protocol architecture

1. Physical layer

• Electrical standard: RS-485 differential signal (same as DMX512), transmission rate of 250kbps.
• Topology: Bus architecture, supports up to 32 devices (expandable to 256).

2. Data link layer

• An RDM packet consists of the start code (0xCC), sub-start code (to distinguish request/response), UID, command class (GET/SET), PID, and data field.
• CRC check ensures data integrity.

• Discovery phase: The controller broadcasts the search command and the device returns the UID response.
• Normal operation: The controller reads and writes device parameters using the GET/SET command.

3. Application layer

• Standard parameters (PID example) :
• DEVICE_INFO (Device Information)
• DMX_START_ADDRESS (DMX start address)
• TEMPERATURE (Device Temperature Monitoring)
• LAMP_HOURS

Four, RDM vs DMX512 key differences