RDM Controller – IS3725

The IS3725 is the RDM boss chip. It works as an RDM Controller, discovering devices, sending queries, and continuously streaming DMX data. This is the perfect chip for implementing an RDM controller. The best part? It requires no libraries, as it works seamlessly over I2C. An SPI version is also available.

How It Works

The chip has two ports:

• I2C Interface: Connects to your microcontroller, FPGA, Arduino, Raspberry Pi, etc. This is where you fill the memory map with DMX values. As the chip is continuously buffering and streaming this data, you only need to write to the memory map when you want to change something (like a LED). The chip handles all timing and frame construction. From I2C, you can also perform RDM discovery and make queries to specific devices to read their responses.
• UART Output: Connects to your favorite RS485 transceiver. The IS3725 sends and receives both DMX and RDM data in TTL levels, so you’ll need to use a transceiver to convert it to RS485 levels. We like the THVD1400 for its robustness and good price, but you can choose whichever fits your needs.

Advantages and Features

Firmware Advantages

• Forget about RDM protocol handling: No need to deal with frame parsing, timings, or UART interrupts
• No libraries needed: Just use standard I2C functions
• Buffers all 512 DMX channels (a full DMX universe) — no need to refresh DMX data
• Perfect for heavily loaded CPUs or ISR-heavy applications
• Arduino, STM32, and Raspberry Pi examples available
• Evaluation board available to make some tests
• Save firmware engineering time

Hardware Advantages

• Save pins on your microcontroller: No need to sacrifice any UART pins as it uses I2C, a shared interface
• Reduce the CPU load of your microcontroller
• Reduce Flash and RAM memory footprint
• Save microcontroller resources (UART, Timers, etc.)
• Schematic design examples available

Compatibility Advantages

• Great for non-deterministic systems (like Raspberry Pi and single-board computers)
• Compatible with 5V I2C serial interfaces
• Compatible with 5V RS485 transceivers
• Supports I2C speeds: 100kHz, 400kHz, and 1MHz
• Ideal for FPGA designs

Production Advantages

• Easy-to-solder SO8N package
• Reels available for pick-and-place machines

Commercial Advantages

• Speeds up development
• Faster prototyping
• Shorter time-to-market