Use the straight-line or loop topology when connecting your devices on the RS-485 bus.
To reduce signal reflections on the RS-485 network when using the straight-line wiring method, connect a terminating resistor (RT) across the (+) and (-) terminal of the last device on the bus. The terminating resistor should match the impedance of the RS-485 cable, typically 120 ohms.
There are a couple of advantages to using the loop topology:
• A single open-circuit condition anywhere on the loop does not result in communications loss for all the other connected devices on the RS-485 bus.
• It does not require termination resistors at any point on the RS-485 bus.
To reduce signal reflections on the RS-485 network when using the straight-line wiring method, connect a terminating resistor (RT) across the (+) and (-) terminal of the last device on the bus. The terminating resistor should match the impedance of the RS-485 cable, typically 120 ohms.
There are a couple of advantages to using the loop topology:
• A single open-circuit condition anywhere on the loop does not result in communications loss for all the other connected devices on the RS-485 bus.
• It does not require termination resistors at any point on the RS-485 bus.
Released for:Schneider Electric Thailand
