Modbus RTU tester for Windows

Serial settings in one dialog

In Connection Setup choose Modbus RTU or Modbus ASCII. Busscope lists the serial ports it finds and lets you type one that is not listed. You set the baud rate (1200 to 115200 are offered, and you can enter another value), data bits (7 or 8), parity (none, even or odd) and stop bits (1 or 2). The response timeout runs from 50 ms to 60 seconds, and a delay between polls keeps slow devices from being flooded.

RS-485 adapters: echo removal and RTS toggle

Many USB-to-RS-485 converters echo what they send or need the host to switch the driver on and off. Busscope has two options for them. Remove echo (RS-485 loopback) drops the copy of your own request that comes back on the receive line. RTS toggle (transmit enable) raises RTS while a frame is sent, for converters that use it as the direction control. If a converter switches direction on its own, leave both off.

Slave IDs and broadcast

Valid slave addresses on a serial bus are 1 to 247. When you pick a reserved ID from 248 to 255 on a serial connection, Busscope warns you. Slave ID 0 is the broadcast address and is only accepted for write functions, because no slave answers a broadcast: sending it is the whole result.

The same tools as for Modbus TCP

Everything else works the same on a serial line. Poll windows read functions 01 to 04 and share the connection. Twelve display formats with four byte and word orders decode floats, long integers and text. Live charts, value labels and cell names help you watch a process. The write dialog covers functions 05, 06, 15, 16, 22 and 23 and asks you to confirm each write.

Troubleshooting a silent device

When a device does not answer, the traffic panel (F4) shows the frames that were sent and received as hex, so you can tell a wrong baud rate or parity from a wrong slave ID. The diagnostics window (F7) reads exception status, comm event counter, slave ID and device identification where the device supports them. The Request Runner can check that a device answers with an exception where the specification says it must, or with TIMEOUT where it must stay silent. If you have a device with poor documentation, the Register Probe scans an address range and reports the readable and the illegal addresses.

Save the setup

Port, speed and framing are stored in the workspace file together with your windows, so a test bench is one double-click away. Log values to CSV or Excel (.xlsx) while you test.