Modbus CRC added for you, on your phone

A Modbus RTU frame ends with a two-byte CRC. Working it out by hand, or in a separate calculator, is slow and easy to get wrong. LinkJig appends it while you type and shows the bytes before you send.

This is a real session on LinkJig's built-in loopback device, which echoes back whatever you send. It works the same on any serial, Bluetooth or TCP link.

Append the checksum

In the terminal, set the send bar to HEX.
Open the checksum menu next to it (it says No checksum) and pick CRC-16/MODBUS.
Type your frame. For "read two holding registers from address 0 of device 1" that is 01 03 00 00 00 02.
Below the field, the full frame appears with the two check bytes highlighted: C4 0B. Tap Send.

Send bar with CRC-16/MODBUS, the preview shows C4 0B appended

What went out and what came back:

20:48:34.264 TX 01 03 00 00 00 02 C4 0B
20:48:34.295 RX 01 03 00 00 00 02 C4 0B

Other checksums

The same menu has SUM8, XOR8, CRC-8, CRC-16/MODBUS, CRC-16/CCITT-FALSE and CRC-32. The checksum is added to the data only; a line ending, if you choose one, goes after it.

Limits

Shown on the built-in loopback device, not on a real Modbus device.
CRC-16/MODBUS is sent low byte first, as Modbus RTU expects.

Try it

Watch the demo on YouTube. LinkJig is on Google Play and the Microsoft Store.