Schneider Electric LUFP9 user manual Field, Size, Frame

6. Configuring the Gateway

Field in the	Size in the	Description
frame	frame
Preset Data	2 bytes	Data Location: Address, in the gateway’s output data memory (16#0202 to
	or more for a	16#03FF), of the item of data to be transmitted in the “Preset Data” field for the
	block of data	query’s frame.
		N.B. The “Data location” field is used for each frame that allows you to
		exchange some data between the Modbus slaves and the DeviceNet master.
		In this case it designates the starting address of the block of data to be
		transmitted.
		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 O:1.x outputs of the
		DeviceNet scanner.
		E.g. The value to be assigned to the ATS48’s CMD register should be placed
		in the gateway’s output data memory area. We will be using the first free
		location starting at an even address, that is to say the one located at 16#0220,
		with the gateway’s default configuration.
		Data length: Length of the block of output data, in the gateway’s memory,
		whose values must be transmitted in the “Preset Data” field of the query’s
		frame. It is expressed in number of bytes.
		N.B. The “Data length” field is always used together with the “Data location”
		field, described above.
		E.g. Since the “Preset Single Register” command is used to write the value of a
		single register (16-bit), the value of the “Data length” field must be set to 2.
		See the documentation for each Modbus slave to find out the maximum
		amount of 8-bit data which can be placed in “Data” type fields in queries and
		responses for this slave. With the ATS48, for instance, it is limited to 30 16-bit
		words.
		Byte swap: Specifies whether the output data bytes to be transmitted to the
		Modbus slave must be swapped before being placed in the Modbus frame or
		not. The three possible values are as follows:

-No swapping ....... Default configuration. The data is sent in the same order as they appear in the gateway’s memory.

-Swap 2 bytes ...... The bytes to be transmitted are swapped two by two. This is the case which must be used by default, because for an item of 16-bit data, the most significant byte is placed first in the Modbus frame, whereas it is always written into the gateway’s memory by a DeviceNet master with the least significant byte first.

-Swap 4 bytes ...... The bytes to be transmitted are swapped four by four. This is rarely used, as it only relates to 32-bit data. The principle is similar to that of the previous case, “Swap 2 bytes”.

E.g. We will be using the “Swap 2 bytes” value, because the two bytes of the value to be written into the ATS48’s CMD register, as transmitted by the SLC500 PLC, are placed into the gateway’s memory in least significant / most significant order.

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