How do I check RS485 A/B polarity?
Do not assign wires from color or A/B letters alone. Compare the converter and device manuals, including their signal definitions and pin views, then document the intended pair. Follow the equipment supplier's procedure for correcting polarity; do not experiment on energized unknown terminals. Keep power, signal reference and protective earth distinct.
Where should RS485 termination be checked?
Review the actual bus topology and existing termination with the device documentation. Termination is a network-design decision, not a resistor to add at every device. Identify built-in termination and biasing before adding components. Record branches and cable lengths so the supplier can review the complete link.
Why does a Modbus connection time out?
Check that the correct serial port and supported driver are selected, then compare baud rate, parity, stop bits, device address and the requested protocol. RS485 specifies an electrical interface, not a guarantee of Modbus compatibility. Isolate a permitted single-device link before adding the rest of the network.
What must be confirmed for the exact converter cable?
Ask for the model's wiring diagram, supported operating systems, driver source, electrical interface and any isolation or power requirements. Do not infer a chipset, isolation rating or terminal arrangement from USB or RS485 labels. Send the comparison log and manuals when the failure remains unresolved.
Common mistakes
- Swapping A/B or adding termination without checking both manuals.
- Assuming a USB connector identifies TTL, RS232, RS485 or an isolated converter.
What to include in your inquiry
- Converter and target device models and manuals
- Pin map, A/B definitions, topology and termination
- Operating system, driver and serial/protocol settings
- Symptoms and results of a controlled single-device test
Use this checklist to prepare a specification. Confirm the final assembly against your equipment documentation and the agreed drawing.