Rockwell Automation 1755-OF8 GuardPLC Controller Systems - Manual (Page 232)

232 Publication 1753-UM001C-EN-P - March 2010
Chapter 19 Use GuardPLC Controller as an Adapter
6. Check the Connected and then the Cache Connections boxes.
The Connected option ensures that messages are sent over a
Class 3 connection, not as unconnected ones.
Cache Connections is the default option. If it is checked, the
connection is opened the first time the controller is in Run mode
and the rung condition is true. In this example, the rung
condition is true when Enable value is true and the timer has
expired (DN flag is set). This connection remains open until the
controller goes to Program mode.
If Cache Connections is unchecked, a connection is opened
every time the controller is in Run mode and the rung condition
becomes true. The Logix controller opens the connection, sends
an explicit message over the new connection and then closes
the connection immediately. The next time the rung condition is
true, the whole sequence is repeated: open connection, send
message, close connection.
7. Build the third rung containing these instructions:
•
Examine on Enable tag
•
Examine on TIMER_CONN.DN
•
Message instruction with the control tag MSG_WRITE
8. Configure the message parameters as follows:
a. Set Service Type to Set Attribute Single.
b. Set Class to 4 (assembly).
c. Set Instance to 121.
This is the assembly instance number that will be written to.
d. Set Attribute to 3 (assembly data).
e. Set Source Element to WriteBuffer.
f. Set Source Length to 4 bytes.
The Source tag can be larger in size than the target GuardPLC
assembly. However, the Source Length should exactly match
the size of the assembly, otherwise an error occurs.