Schneider Electric LUFP7 Read Holding Registers Command 16#03, Frame Field Value or properties

13. Appendix F: Modbus Commands

Chapter 6.11 Adding and Setting Up a Modbus Command, page 68, 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 70, and chapter 6.11.3 Adding a Special Modbus Command, page 80, 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.

13.1. “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 (PF)	- Number of output / internal registers
	Number of points (Pf)
Response	Byte count	- Number of data bytes = Number of output / internal registers × 2
	Data (first register / MSB)	- Byte swap = “No swapping” (or “Swap 2 bytes”)
	Data (premier registre / Pf)
		- Data length = Value of the “Byte count” field
	………
	Data (dernier registre / PF)	- Data location = Address in the gateway’s input memory
	Data (dernier registre / Pf)

13.2. “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 = “No swapping” (or “Swap 2 bytes”)
		- Data length = 16#0002
	Preset data (LSB)
		- Data location = Address in the gateway’s output memory
Response	Register (MSB)	- Byte swap = “No swapping” (or “Swap 2 bytes”)
		- Data length = 16#0002
	Register (LSB)
		- Data location = Address in the gateway’s input memory
	Preset data (MSB)
		N.B.: These data are an echo to the query. So in most cases there is no
	Preset data (LSB)
		need to feed them back to the Profibus-DP 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 Profibus-DP inputs (16#0002- 16#00F3), you’d better link it with the address 16#0400.

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