Schneider Electric LUFP7 user manual Appendix F Modbus Commands

13. Appendix F: Modbus Commands

Only the Modbus commands shown in the right-hand table are supported by the gateway. The structure of the query and response frames for each of these commands is then described in the following chapters.

Function code		Broadcast (1)	Modbus command
3	16#03	—	Read Holding Registers
6	16#06	Yes	Preset Single Register
16	16#10	Yes	Preset Multiple Registers

(1)The content of this column shows whether the command can be added (“Yes”) or not (“—”) to the list of a broadcaster node’s commands, known as “Broadcaster” in AbcConf.

In the following chapters, each byte of the query and response frames of a Modbus command are described, one after another, with the exception of the fields shown opposite. These are always present in the queries and responses of all Modbus commands.

The “Slave Address” and “Function” fields are the first two bytes of these frames. The two bytes of the “Checksum” are their last two bytes.

Slave Address	- Value cannot be changed (Modbus
	address: 1 to 247. Addresses 125,
	126, and 127 prohibited)
Function	- Value cannot be changed (code of
	the Modbus command)
… Other	… Specific features of
fields …	Modbus commands …
Checksum (Lo)	- Type of error check
Checksum (Hi)	- Number of the 1st byte checked

The descriptions of the Modbus frames which appear in the following chapters are mainly intended to help you to configure the gateway’s Modbus exchanges using AbcConf. Please see the documentation of each Modbus slave to check for any restriction regarding these frames (number of registers which can be read or written in a single Modbus command, for example).

It is a better idea to get hold of a standard Modbus document, such as the guide entitled Modicon Modbus Protocol Reference Guide (ref.: PI-MBUS-300 Rev. J), so that you can see the correspondence between the elements displayed in AbcConf and the content of the corresponding Modbus frames. Here is an example of a correspondence for a full frame (including the start and end of frame fields shown above), based on the “Read Holding Registers” Command (16#03) (see chapter 13.1, page 109):

	Elements under AbcConf
Modbus	Slave Address
query	Function
	Starting Address (Hi, Lo)
	Number of points (Hi, Lo)
	Checksum
Modbus
	Slave Address
response	Function
	Byte count
	Data
	Checksum

Modbus frame fields

Slave no.

Function no.

No. of the 1st word (MSB / LSB)

Number of words (MSB / LSB)

CRC16 (LSB / MSB)

Slave no.

Function no.

Number of bytes read

Value of 1st word (MSB / LSB)

…………………………………

Value of last word (MSB / LSB)

CRC16 (LSB / MSB)

Size

1byte

1byte

2 bytes

2 bytes

2 bytes

1byte

1byte

1byte

2 bytes

…………

2bytes

2bytes

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