2.2 Installation and RS-485 Wiring
2.2 Installation and RS-485 Wiring
In this lesson: you will be able to physically land, terminate, and address the RS-485 bus correctly, and understand the bus speed and wake-up behaviour.
The bus is the foundation
Network 8000 controllers talk to each other, and to the gateway, over an RS-485 serial bus. Getting the wiring right is the foundation of everything else.
Topology and polarity
RS-485 is a two-wire differential bus. Every device connects to the same pair — commonly labelled A and B, or plus and minus — in a daisy chain. Not a star, not a ring: one wire in, one wire out, device to device. Keep the polarity consistent the whole way; swapping A and B on one device breaks communication for that device.
Land the two bus wires on the gateway's RS-485-1 terminals. Bring the cable shield through and ground it at one end only, to avoid ground loops.
Termination and addressing
Termination. RS-485 wants a terminating resistor at each physical end of the bus — the two devices furthest apart. Missing or doubled-up termination shows up as intermittent comms and CRC errors, and it is the most common wiring fault we see. Terminate the two ends, and only the two ends.
Addressing. Every controller on the bus needs a unique address. Two controllers sharing an address will collide and neither will discover cleanly. Set addresses per the controller's own procedure before you rely on discovery. The valid address range is 1 to 247.
Bus speed and wake-up
Bus speed is a Network 8000 quirk worth understanding. Sleeping controllers listen at a slow 1200 baud. To wake them, the gateway first speaks at 1200 baud, then switches everyone up to 19200 baud for normal operation. You do not configure this — the gateway handles the wake-up and the speed change automatically during discovery. There is no baud rate to tune. Just know that “1200 to wake, 19200 to work” is normal and expected.
Before you power on the gateway: double-check polarity end to end, confirm termination at both ends, and confirm every controller has a unique address. Fix those three on the bench and discovery becomes trivial. Skip them and you will be chasing ghosts.
Key points
- Wire the bus as a daisy chain (device to device), keeping A/B polarity consistent the whole way.
- Ground the shield at one end only; terminate at the two physical ends of the bus and only there.
- Every controller needs a unique address (range 1–247); duplicates collide and will not discover cleanly.
- “1200 to wake, 19200 to work” is automatic — there is no baud rate to tune.
- Intermittent comms/CRC errors usually mean wrong termination, reversed polarity, or duplicate addresses.
Check your understanding
- What physical topology does the RS-485 bus require?
- Where do the terminating resistors go?
- The gateway wakes controllers at one speed then runs at another. What are the two speeds, and do you configure them?
- Two controllers will not discover cleanly and comms is intermittent. Name two likely wiring causes.