CTI 2572-B / 2500C-2572-B Installation and Operation Manual 23
• Number of Elements: Select the number of data elements to read or write
• Destination Element: For a read operation, this is the Control Logix Tag Name. For a write operation, this
is the 505 Tag Name.
4. Specify the Communication options for each Message Block. This includes the path to the target 2572-B
module.
Defining the Control Logix Data Tags
First, we will need to define some Control Logix tags. We will define two tags, one to hold the data read from
the 505 PLC and the other for the data we will write to the 505 PLC. Different formats are used for the read
and the write operations to illustrate the difference in accessing signed and unsigned V memory data.
The tag named VMEMREAD will be used to store the data read from the 505 PLC. The tag data type is defined
as a 32 bit signed integer. This is done because we want to read unsigned integers from the PLC, whose values
may exceed the maximum that can be stored in a 16 bit signed integer (+32,767). Note that the Control Logix
processor does not support unsigned integer tags. This tag is dimensioned to hold 100 values.
The tag named VMEMWRITE will be used to store the data that will be written to the 505 PLC. Since we are
writing signed 16 bit integers to the 505 PLC, this tag type is defined as a signed 16 bit integer. This tag is
dimensioned to hold 50 values.
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