Schneider Electric LUFP9 user manual Adding a Special Modbus Command

6. Configuring the Gateway

Field in the	Size in the	Description
frame	frame
Slave Address	1 byte	Identical to that of the query’s “Slave Address” field.
Function	1 byte	Identical to that of the query’s “Function” field.
Register	2 bytes	Identical to that of the query’s “Register” field, since the Modbus response of
		any “Preset Single Register” command is an echo to the corresponding query.
		Here you should also enter the address of the memory object to which the
		command relates.
		E.g. Enter the value 400, converted to 16#0190 by AbcConf.
Preset Data	2 bytes	Data Location: Address, in the gateway’s input data memory (16#0002 to
	or more for a	16#01FF), of the item of data received in the “Preset Data” field for the
	block of data	response’s frame.
		N.B. As far as possible, ensure that the data is located at even addresses in
		order to align the Modbus data (in 16-bit format) on the I:1.x inputs of the
		DeviceNet scanner.
		E.g. The value sent back as an echo to the command must be placed in the
		gateway’s input data memory area. We will be using the first free location, that
		is to say the one located at 16#0020, with the gateway’s default configuration.
		Data length: Length of the block of input data received in the “Preset Data”
		field of the response frame. It is expressed in number of bytes.
		E.g. The value of the “Data length” field must be set to 2.
		Byte swap: Identical to that of the query’s “Byte swap” field.
		E.g. We will also be using the “Swap 2 bytes” value, for the same reasons as
		with the query.
Checksum	2 bytes	Error check type: Identical to that of the query’s “Error check type” field.
		Error check start byte: Identical to that of the query’s “Error check start bype”
		field.
		However, these two fields cannot be changed by the user and their values are
		greyed out to reflect this. AbcConf updates the values of these fields
		automatically using those of the query’s “Error check type” and “Error check
		start byte” fields.

6.11.3. Adding a Special Modbus Command

Apart from the standard Modbus commands covered in the previous chapter, it is possible to create two types of special Modbus commands: Modbus commands using the same template as standard commands and Modbus commands whose nature and frame content can be completely changed by the user.

6.11.3.1. Modbus Commands Based on Standard Commands

You create a command of this type from the “Select Command” window (see chapter 6.11.2 With a Generic Modbus Slave, page 63), by choosing “Add Command” from the “Command” menu. The window shown at the top of the next page appears. It shows the structure of the future command’s query and response frames, which will then be added to the list of available Modbus commands. This structure includes the standard elements, that is to say the “Slave Address”, “Function” and “Checksum” fields, described in previous chapters.

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