Watlow Series PD - Manual (Page 161)

3.0 Communications between ControlLogix & PD
After configuration of the PD both real-time I/O connections (implicit messaging) and non-
time critical (explicit messaging) communications are enabled. All information transferred
between the control and the PD will be achieved through either the Static or Dynamic
assemblies described above. All implicit messages are sent and received cyclically at the
rate of the Requested Packet Interval (RPI) where explicit messages are typically initiated via
a message instruction in the control program. Generally speaking, explicit messages are
used as a tool for configuration. As an example, to change the size of the PD assembly from
the standard static assembly to the dynamic assembly one would use a message instruction
to accomplish this.
3.1 Ladder Logic Examples
In the ladder logic examples that will follow it would be good to note how the PD
and its associated tags were configured. First, let’s take a look at the tags that were
created for the PD upon completion of the module configuration. Bringing the focus to
the screen shot below, notice that the PD was given the name “Watlow_PD”, the
Comm Format was set at INT, and the Static Assemblies are being used for both the
input and output assemblies.
Upon completion of the PD configuration the Controller Tags are automatically
generated for all assemblies as can be seen in the resultant screen shot below.
Figure 3.1b
Figure 3.1a
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