3.1. Defining commands

3.1.1. Standard commands
3.1.1.1. Read File Record (20)
3.1.1.2. Write File Record (21)
3.1.1.3. Read Device Identification (43/14)
3.1.2. Custom commands
3.1.3. Sending raw data

You can use the Define Command page to define and send Modbus commands.

A command definition consists of:

When you have entered a command definition, you can click the Test button to send the command to the slave. The result of sending the command will be displayed in the page. Any differences between the actual and expected results (i.e. outcome and values) will be highlighted in red.

If you know that the actual outcome and values from the slave are correct, you can use them as the expected outcome and values by clicking the Expect actual button. This is often much quicker than manually entering expected values.

If you want to save the command definition, enter a unique name for the command in the Name field and click the Save button. All saved command definitions are listed in the Command table.

You can provide a description of the command in the Description field. ModTest displays the description, but does not use it in any other way. It is purely for your benefit, to remind you of what the command is used for.

The Reset button will restore the values to their last saved state.

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