How Do You Wire an IO Module to a DDC Controller?

The Founder's Explanation (Teach Exactly This Way)

"Like a telephone line. Two wires must go end to end, same way, no crossing. Every phone needs its own number — two same numbers, confusion. And at the two ends of the line, a proper stop, otherwise echo. RS485 bus is exactly this — A to A, B to B, one address each, termination at the ends. One mistake, whole line silent."

Teaching the Concept

The Telephone Line A phone line is two wires running end to end, never crossed. Every phone on it needs its own number, or the exchange is confused. And the line needs a proper end, or the signal echoes back. An RS485 bus between a controller and its IO modules follows the very same rules. One loose wire or duplicate number silences the whole line. The Wiring Checklist ``` RS485: CONTROLLER <-> IO MODULE(S) 1. Daisy-chain A->A, B->B, GND->GND (no star wiring) 2. Keep A/B polarity consistent end to end 3. Set a UNIQUE address per module (DIP / software) 4. Match baud rate + parity to the controller 5. Fit end-of-line termination (120 ohm) at both ends 6. Feed clean, correctly-rated 24V ``` When It Still Will Not Talk ``` No comms? check A/B not swapped check for duplicate address check EOL termination present check baud/parity match check 24V present and grounded ``` A field bus rewards discipline — same polarity, unique address, terminated ends, and the panel simply works.

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Related Topics

• IO list best practices and wiring color codes — laying out and wiring an IO list cleanly
• What is a BMS DDC controller? — the programmable brain that runs the logic
• Browse all IO List & Wiring topics — more from this section of the EnSmart BMS Library