RS485 Software: Monitor, Sniff and Log RS485 Data on Windows
RS485 is the multi-drop, two-wire bus used by MODBUS RTU meters, PLCs, sensors and drives. On a PC it appears as a COM port through an RS485 converter, so it uses the same software as RS232, with two differences: the software must control the transmit direction, and listening to a running bus needs a proper tap. This page covers both.
On this page: Which tool for which job · Monitor and terminal · Sniff a live bus · Log MODBUS RTU and other RS485 data · RS485 to Ethernet · FAQ
Which RS485 tool do you need?
| You want to | Tool | Price |
|---|---|---|
| Send requests to an RS485 device by hand and read the replies | Advanced Serial Port Monitor in RS485 mode | $60 |
| Poll a MODBUS RTU slave, check register values, or pretend to be a slave | Advanced Serial Port Monitor with the MODBUS plugin | included |
| Listen to the traffic between a master and its slaves without interfering | Advanced Serial Port Monitor with a tap cable, see below | $60 |
| Find which addresses are alive on the bus | online MODBUS scanner or the device scan plugin | free |
| Log MODBUS RTU registers or any RS485 data stream to files, Excel or SQL, unattended | Advanced Serial Data Logger | $110 |
| Give MODBUS TCP masters access to RS485 slaves, or the reverse | MODBUS Gateway | $99 |
| Sync RS485 MODBUS registers with SQL, MQTT or OPC in both directions | Datatag Link | $99 |
RS485 monitor and terminal
Advanced Serial Port Monitor works with RS485 through any RS232-to-RS485 or USB-to-RS485 converter. Select the RS485 mode in the port settings and the program raises RTS while it transmits and drops it to receive, which is what converters without automatic direction control need. Data is shown in ASCII and hex with timestamps, and every session can be logged to a file.
RS485 Port Monitor
Monitor RS485 data or send commands to an RS485 device. Select the RS485 mode option in the settings; the MODBUS plugin adds master and slave simulation.
Sniffing a live RS485 bus
Because RS485 is half duplex, requests and responses travel on the same pair of wires. That makes passive monitoring simple: connect the A and B lines of the bus to a converter on the monitoring PC, set the same baud rate and framing, and Advanced Serial Port Monitor shows every request and every reply in order. The monitoring converter only listens, so the master and the slaves are not disturbed. Use this to find collisions, timeouts, wrong slave addresses, and devices that answer on the wrong settings.
Advanced Serial Port Monitor
In sniffer mode with a tap on the A and B wires it records both directions of the bus traffic on a single COM port.
Logging MODBUS RTU and other RS485 data
Most RS485 devices speak MODBUS RTU or ASCII. Advanced Serial Data Logger polls them with its MODBUS plugin: you list the registers, the poll interval and the data types, and the logger writes the values to a log file, Excel, or a database, as a Windows service. Devices with a plain text protocol are handled with the built-in parser. The power meter library has ready register maps for 178 brands and models, so many meters need no manual reading at all.
Guides: configuring the MODBUS master, MODBUS polling how-to, MODBUS to a database, writing to a MODBUS device, all MODBUS guides.
RS485 Data Logger
Polls MODBUS RTU/ASCII and other RS485 devices in RS485 mode and exports the values to files, Excel or databases, fully automatically.
RS485 to Ethernet
When a SCADA or PLC on the network needs an RS485 device, MODBUS Gateway converts MODBUS TCP to MODBUS RTU in real time on a PC with an RS485 port, with address mapping so that several TCP masters can share one bus. For any other RS485 protocol, TCP COM Bridge publishes the converter's COM port over TCP so a remote program can open it as a virtual COM port. Both run as services.
TCP COM Bridge
TCP COM Bridge - connects two physical or virtual COM ports to each other over network!
Frequently asked questions
Do I need special hardware?
Yes, a converter: USB-to-RS485 or RS232-to-RS485. Converters with automatic direction control work in the normal mode; converters that expect the PC to switch direction need the RS485 mode in our software.
Can I monitor the bus while the PLC is running?
Yes. A second converter connected in parallel to the A and B lines only receives. Set it to the bus baud rate and parity and watch the traffic in Advanced Serial Port Monitor.
What about four-wire RS422?
RS422 is full duplex with separate transmit and receive pairs. It needs no direction control and works in the normal mode of every tool here.
Can one logger poll several devices on one bus?
Yes. Each slave address gets its own set of requests, and the logger cycles through them. The polling how-to explains the right way to poll multiple devices.
Related categories
RS232 software · COM port software · MODBUS software · Data logger software · TCP/IP and UDP software