RS485 Termination Resistors & Interface Modules
RS485 termination and serial-interface components
This mixed collection contains 120Ω termination resistors, RS485 transceiver ICs and TTL-to-RS485 boards, USB and RS232 converters, hubs, repeaters, surge protection, and Modbus sensor or I/O modules. Some listings are CAN-bus devices, analog-output alternatives or unrelated resistors. Choose the physical-layer function and exact variant before ordering.
What does an RS485 terminating resistor do?
A termination placed across the differential pair at a bus end can reduce reflections when the cable's characteristic impedance and signaling conditions call for it. A nominal 120Ω value is common, but the correct arrangement depends on the cable, topology, transceiver and system design. Termination is different from fail-safe biasing, and excessive or duplicated termination increases driver load. Do not assume every RS485 node needs its own resistor.
Products and important differences
- Discrete 120Ω resistors: selected through-hole 1/4W listings and resistor packs. Verify tolerance, power and installation method for the selected product.
- CAN DB9 termination: a listed adapter places 120Ω between specified CAN pins 2 and 7. CAN and RS485 can use similar resistance values but are different interfaces; a CAN pinout is not an RS485 pinout.
- RS485 transceivers and modules: MAX3485/MAX485 family ICs and automatic-direction TTL-to-RS485 boards require their stated supply and logic levels. A module title does not establish on-board termination or isolation.
- Converters: USB, USB-C, RS232, Ethernet, Wi-Fi, cellular and long-range gateway products need the correct host connector, protocol, drivers, supply and signal mapping.
- Hubs and repeaters: multiport, rail-mounted and isolated options have product-specific port count, power input, grounding and termination requirements.
- Modbus instruments: RTD, NTC, voltage, current, relay and I/O products are active devices that communicate over RS485 on certain variants; analog-output versions are not automatically RS485 versions.
Selection steps
- Identify whether you need a passive terminator, transceiver, converter, repeater or full Modbus device.
- Check RS485 versus CAN, RS232 or TTL levels; shared connectors do not establish protocol compatibility.
- For termination, verify differential-pair impedance, resistor value, placement and total load.
- Confirm two-wire or four-wire topology, half- or full-duplex operation and A/B labeling on the actual devices.
- Check supply voltage, logic voltage, baud rate, cable length, connector and pinout.
- For active products, verify isolation, surge protection and termination only where supported by product documentation.
- For Modbus RTU, confirm device address, baud rate, parity, register map and supported function codes.
Boundary products and safety
Generic 0201, 0805, metal-film, 2512 low-ohm and RX24 power resistors, photoresistors, potentiometers and resistor networks in this collection are not automatically suitable RS485 terminators. A 120Ω option in a general resistor listing still requires suitable package, power and connection. High-input-voltage transducers and mains-powered options require their own electrical ratings and safe installation practices; do not infer isolation from an RS485 output. Preserve the exact product membership while using each product page to verify specifications.
Ordering checklist
- RS485, CAN, RS232 or TTL interface
- Passive termination or active communication function
- Nominal impedance, resistance, tolerance and power
- Bus wiring, pinout and connector
- Supply and logic voltage; duplex mode
- Isolation and protection evidence if required
- Modbus settings, register documentation and selected output option
- Pack quantity and physical mounting
Frequently asked questions
Where should a 120Ω RS485 terminator go?
Where the designed bus topology requires it, typically at the ends of the main cable rather than at every device. Follow the equipment and cable specifications.
Is CAN termination interchangeable with RS485 termination?
No. The nominal resistance may be similar, but connector pins, protocol and network design must be checked separately.
Does a MAX485 module include a terminating resistor?
Not necessarily. Inspect the selected board schematic or product documentation.
Is termination the same as fail-safe biasing?
No. Termination addresses line reflections; biasing establishes an idle differential state where needed.
Are all voltage and current transmitters here RS485 devices?
No. Several listings also offer 4–20mA, relay or analog-voltage output variants. Select the actual interface option.
