User`s manual

Watlow EZ-ZONE™ Communications • 35 • Chapter 3 EtherNet/IP
Communications between ControlLogix &
the EZ-ZONE™ PM
Configuring the PM enables both real-time I/O
connections (implicit messaging) and non-time critical
(explicit messaging) communications. Information will
be transferred between the control and the PM using
either implicit and or explicit connections. 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 instruc-
tion in the control program. It is recommended that
the RPI be set above 100ms. Generally, explicit mes-
sages are used as a tool for configuration. For example,
to change the default T-to-O or O-to-T assembly struc-
ture in the PM from the factory defaults as defined
above, the user would use an explicit message instruc-
tion.
Ladder Logic Examples
In the ladder logic examples that follow, please
note how the PM and its associated tags were config-
ured.
First, let’s take a look at the “Comm Format”
briefly discussed earlier with a recommendation to
configure it as INT. In this section we will see why.
One of the advantages of using the Logix family
of controls is that users can define their own data
types. Creating two unique, user-defined data types
(T to O and O to T) makes programming the PLC to
communicate with the Watlow PM controller very
easy. The name given for these data types is up to
the user. In this example, the user-defined data
types and styles were created to match the default
PM O-to-T and T-to-O assemblies.
Notice in Figure 3.4 (PM T to O) that the first
location is identified as "Device Status." This does
not represent one of the 20 members, and it is re-
quired. Currently, if bit 16 is set to 1, as shown in
figure 3.2 below (PM to PLC), it indicates valid
communications between the Ethernet card and the
PM. If set to 0, communications have failed.
Figure 3.2
Figure 3.3 & 3.4
Now, to use the new data types defined above. Two controller tags where created (see figure 3.5 & 3.6) and
when prompted for the data type, the user-defined data types defined above were selected.