EtherNet/IP Explicit Message Example: Read Modbus Object
Original instructions
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Overview
The following unconnected explicit messaging example shows you how to use the DATA_EXCH function block to read data from a remote device.
You can perform the same explicit messaging service using the EtherNet/IP Explicit Message window.
Implementing the DATA_EXCH Function Block
To implement the DATA_EXCH function block, create and assign variables for the following blocks:
Configuring the Address Variable
The Address variable identifies the explicit message originating device (in this example, the Ethernet communication module) and the target device. Note that the Address variable does not include the Xway address elements {Network.Station} because we are not bridging through another PLC station. Use the ADDM function to convert the following character string to an address:
ADDM(‘0.1.0{192.168.1.6}UNC.CIP’), where:
Configuring the ActionType Variable
The ActionType variable identifies the function type for the DATA_EXCH function block:
Variable
Description
Value (hex)
ActionType
Transmission followed by wait for response
16#01
Configuring the DataToSend Variable
The DataToSend variable identifies the type of explicit message and the CIP request:
Variable
Description
Value (hex)
DataToSend[0]
CIP request service information:
  • High byte = request size in words: 16#02 (2 decimal)
  • Low byte = service code: 16#4E (78 decimal)
16#024E
DataToSend[1]
CIP request class information:
  • High byte = class: 16#44 (68 decimal)
  • Low byte = class segment: 16#20 (32 decimal)
16#4420
DataToSend[2]
CIP request instance information:
  • High byte = instance: 16#01 (1 decimal)
  • Low byte = instance segment: 16#24 (36 decimal)
16#0124
DataToSend[3]
Location of first word to be read):
  • High byte = 16#00 (0 decimal)
  • Low byte = 16#31 (49 decimal)
16#0031
DataToSend[4]
Number of words to read:
  • High byte = attribute: 16#00 (0 decimal)
  • Low byte = attribute segment: 16#01 (1 decimal)
16#0001
Viewing the Response
Use a Control Expert Animation table to display the ReceivedData variable array. Note that the ReceivedData variable array consists of the entire data buffer.
To display the CIP response, follow these steps:
Step
Action
1
In Control Expert, select Tools → Project Browser to open the Project Browser.
2
In the Project Browser, select the Animation Tables folder, then click the right mouse button. A pop-up menu appears.
3
Select New Animation Table in the pop-up menu. A new animation table and its properties dialog both open.
4
In the Properties dialog, edit the following values:
Name
Type in a table name. For this example: ReceivedData.
Functional module
Accept the default <None>.
Comment
(Optional) Type your comment here.
Number of animated characters
Type in 49, representing the size of the data buffer in words.
5
Click OK to close the dialog.
6
In the animation table’s Name column, type in the name of the variable assigned to the RECP pin: ReceivedData and press Enter.
Result: The animation table displays the ReceivedData variable.
7
Expand the ReceivedData variable to display its word array, where you can view the CIP response contained in the ReceivedData variable.
NOTE: Each array entry presents 2 bytes of data in little endian format, where the least significant byte is stored in the smallest memory address. For example, ‘CE’ in word[0] is the lower byte, and ‘00’ is the upper byte.