Instruction Manual

Being able to create these user defined data types allows for a much less complex
program, making it easier for all to understand. The last step prior to getting to the
programming is to create a tag or tags that will use these data types. There will be
one tag created for the PD inputs and another for the PD outputs. The two files that
were created to use these data types were named PD_O2T (ControlLogix to PD) and
PD_T2O (PD to ControlLogix). In defining and then using these data types in the
Program, simple instructions (i.e., COP) can be used to transfer all assembly
information between ControlLogix processor and the PD. Because the data type
“PD_Static_Assembly_Control2PD” matches up byte for byte with the system
generated tag “Watlow_PD:0”, and the fact that the copy (COP) instruction within the
ControlLogix does a byte for byte transfer the programmer does not need to do any
format conversions.
3.1.1 Implicit Ladder Logic Examples
I/O connections provide dedicated, special purpose communication paths
between a producing application and one or more consuming applications.
Application-specific I/O data moves through these ports and is often referred to as
implicit messaging. As this relates to the PD, the Static Assembly (see sections
2.2.1 and 2.2.3 above) is used to send and receive this I/O data. In the event that
the user would want to read or write to different attributes, the Dynamic Assembly
is provided to allow the user to increase the assembly size including those
attributes of their choice.
To better understand the ladder logic example below some of the tags used are
defined below:
Figure 3.1d
Figure 3.1.1a
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