Working with Derived Data Type Variables
Original instructions
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Derived Data Type Variables
When you click on the Update application button, Control Expert creates a collection of derived data types and variables. These are used by Control Expert to support communication and data transfer between the PLC and the various local slaves, remote devices, and their I/O items. You can access these derived data types and variables in the Control Expert Data Editor and add them to a user-defined Animation Table, where you can monitor read-only variables and edit read-write variables.
Use these data types and variables to:
Identifying Derived Variables in the Data Editor
To view your Control Expert application’s derived data type variables:
Step
Description
1
In the Project Browser, navigate to and double-click the left mouse button on Variables & FB instances → Derived Variables:
2
The Data Editor opens, displaying the Variables page:
NOTE:
  • A check mark appears in the DDT checkbox. (If not, select the DDT checkbox to display these variables.)
  • The red arrow and lock icons indicate the variable name was auto-generated by Control Expert based on the configuration of the local slave or remote device and cannot be edited.
Displaying the Order of Input and Output Items in PLC Memory
The Data Editor displays the address of each input and output variable. Click once on the Address column header to sort input and output addresses in ascending order. When you open the first input and output variables, you can see both the connection health bits and the connection control bits:
Note the order of inputs and outputs in the above example. Recall that the user defines the size and location of inputs and outputs. However, within the reserved area for both inputs and outputs, Control Expert assigns addresses to variables in the following order:
Inputs
Order
Outputs
Health bits 1
1
Control bits 1
Modbus TCP input variables 2
2
Modbus TCP output variables 2
Local Slave input variables 3
3
Local Slave output variables 3
EtherNet/IP input variables 2
4
EtherNet/IP output variables 2
1. Health and control bits are sub-ordered as follows:     i. by device type: a. Modbus TCP; b. local slave; c. EtherNet/IP     ii. within each device type:
a. by device or local slave number
b. within a device: by connection number
2. Device variables are sub-ordered as follows:     i. by device number     ii. within a device: by connection number     iii. within a connection: by item offset 3. Local slave variables are sub-ordered as follows:     i. by local slave number     ii. within each local slave: by item offset
NOTE: When a device is added to or removed from the project, or when the active status of an existing device or a local slave changes, the specific location of inputs and outputs in PLC memory also changes.
Identifying the Connection Health Bits
The Ethernet communication module can support up to 128 connections to remote devices. The health of each connection is represented in a single bit value. A health bit value of:
The health bits are contained in a 32-byte array in the Variables page of the Data Editor. To display offline this byte array, first sort the variables in ascending order of address, then open the first input variable as shown below:
To determine which health bit is mapped to a specific remote device connection, in the Device Editor for the Ethernet communications
Step
Action
1
In the Device Editor for the Ethernet communication module, under the Device List node, navigate to and select:
  • for Modbus TCP devices: the main device node
  • for EtherNet/IP devices: a connection node
2
For a Modbus TCP device, open the Request Setting page and look for the Connection Bit number:
In the above example (which displays the left portion of a truncated Request Setting page), the Connection Bit value of 0 maps to the first bit in the first byte of the HEALTH_BITS_IN array, which can be represented as HEALTH_BITS_IN[0].0.
3
For an EtherNet/IP device, open the Connection Settings page and look for the Connection Bit number:
In the above example, the Connection Bit value of 2 maps to the third bit in the first byte of the HEALTH_BITS_IN array, which can be represented as HEALTH_BITS_IN[0].2.
4
For a local slave, open the local slave configuration page and look for the Connection Bit number:
Monitoring Connection Health Bits in an Animation Table
Use an animation table to monitor the status of connection health bits and other variables. To add health bits to an animation table, follow these steps:
Step
Action
1
In the Project Browser, select the Animation Tables node and click the right mouse button. A pop-up menu opens.
2
Select New Animation Table.
3
In the New Animation Table dialog, type in values for the following fields:
Name
Type in a name for the new animation table. In this example, type in Connection_Health_Bits.
Number of animated characters
Accept the default value of 100.
The completed dialog looks like this:
4
Click OK. The dialog closes and the new Connection_Health_Bits animation table opens.
5
Double-click on the first empty row in the Name column, then click the ellipsis button . The Instance Selection dialog opens.
6
In the Instance Selection dialog, navigate to and select the entire HEALTH_BITS_IN array:
7
Click OK to add the array to the Connection_Health_Bits animation table:
Keep in mind that each row represents a byte, which contains eight individual connection health bits. When the DTM for the Ethernet communication module is connected to the physical module, the Value field displays a value for the entire byte.
Modifying Connection Control Bits in an Animation Table
You can also use an animation table to modify the value of a control bit, toggling it on or off.
NOTE: Using control bits to toggle a connection on or off (as described below) is the preferred way of regulating communication with a remote device. Toggling a connection control bit on and off does not affect the address location of I/O items. In either case—on or off—the I/O items remain a part of the configuration at the same address locations.
By contrast, enabling and disabling the Active Configuration property for a device or local slave either adds I/O items to, or removes I/O items from, the application. This has the rippling effect of changing the addresses not only for the items of the enabled/disabled device, but also for I/O items relating to other devices in the configuration.
The following example shows you how to add connection control bits to the Connection_Health_Bits animation table that you created, above, and use the animation table’s Modification function to toggle control bits on or off:
Step
Action
1
With the Connection_Health_Bits animation table open, double-click on the next empty row in the Name column, then click the ellipsis button . The Instance Selection dialog opens.
2
In the Instance Selection dialog, navigate to and select the entire CONTROL_BITS_OUT array:
3
Click OK to add the control bit array to the Connection_Health_Bits animation table:
Keep in mind that each row represents a byte, which contains eight individual connection control bits. When the DTM for the Ethernet communication module is connected to the physical module, the Value field displays a value for the entire byte.
4
With the DTM for the Ethernet communication module connected to the physical module, double click in the Value column for the row (byte) that contains the control bit you want to toggle.
5
Type a value that toggles the bit (or bits) in the byte you want to change to on or off. For example, suppose the Value field of the control bit displays an initial value of 7. This indicates that the first three (0, 1, and 2) are not established. If you intend to establish the third connection (connection 2), modify the corresponding bit to 0 (type a value of 3).
NOTE: When the control bit is 0, the connection is established. When the control bit is 1, the connection is closed.
6
On your keyboard, press Enter. The control bit for the third connection (i.e. connection number 2) is toggled off.