Schneider Electric LUFP9 Read Holding Registers Command 16#03, Frame Field Value or properties

11. Appendix E: Modbus Commands

Chapter 6.11 Adding and Setting Up a Modbus Command, page 62, also shows a few examples of correspondences between the elements displayed in AbcConf and the corresponding Modbus frame fields.

See also: Chapter 6.11.2 With a Generic Modbus Slave, page 63, and chapter 6.11.3 Adding a Special Modbus Command, page 73, if the implementation of one of these commands would be incompatible with its implementation in the gateway, for example. You then have to create a special Modbus command to compensate for this incompatibility.

N.B. here, the notions of “input” and “output” (and assimilated) are irrelevant, as all Modbus commands have access to all of a Modbus slave’s memory. However, these names are retained in order to comply with the terms used in the standard Modbus documentation.

11.1. “Read Holding Registers” Command (16#03)

Frame	Field	Value or properties
Query	Starting Address (MSB)	- Address of the 1st output / internal register
	Starting Address (LSB)
	Number of points (MSB)	- Number of output / internal registers
	Number of points (LSB)
Response	Byte count	- Number of data bytes = number of output / internal registers × 2
	Data (first register / MSB)	- Byte swap = “Swap 2 bytes” (or “No swapping”)
	Data (first register / LSB)
		- Data length = Value of the “Byte count” field
	………
	Data (last register / MSB)	- Data location = Address in the gateway’s input memory
	Data (last register / LSB)

11.2. “Preset Single Register” command (16#06)

Frame	Field	Value or properties
Query	Register (MSB)	- Address of the output / internal register
	Register (LSB)
	Preset data (MSB)	- Byte swap = “Swap 2 bytes” (or “No swapping”)
		- Data length = 16#0002
	Preset data (LSB)
		- Data location = Address in the gateway’s output memory
Response	Register (MSB)	- Byte swap = “Swap 2 bytes” (or “No swapping”)
		- Data length = 16#0002
	Register (LSB)
		- Data location = Address in the gateway’s input memory
	Preset data (MSB)
		N.B. This data is an echo to the query. So in most cases there is no need
	Preset data (LSB)
		to feed them back to the DeviceNet master.

Instead of creating a link between the echo of the response to the “Preset Single Register” command (16#06) and the memory area dedicated to the DeviceNet inputs (16#0002- 16#01FF), you’d better link it with the address 16#0400.

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