Rockwell Automation 1747-L55x,D174710.4 SLC 500 Ethernet - Manual (Page 32)

4–2 Communicating on the Ethernet Network
Publication 1747-10.4
The SLC 5/05 processors use the MSG instruction to communicate
over the Ethernet network. The table below describes MSG
instruction parameters for Ethernet.
Parameter Value
Supported MSG Commands
485 CIF Read
485 CIF Write
PLC5 Typed Read
PLC5 Typed Write
SLC 500 CPU Read
SLC 500 CPU Write
Message Sizes (Channel 1)
256 elements maximum, with two exceptions:
•
PLC5 Type MSG, Timer File – 201 elements maximum
•
All MSG Types, String File – 23 elements maximum
Modifying Connections
The user may change a MSG instruction destination while the processor is in
the RUN mode. If a MSG instruction’s destination IP address changes, the
next time the MSG instruction executes, a new connection is established with
the new destination node. The old connection remains open as long as either
another MSG instruction was sharing it, or the connection inactive timer has
not expired.
Limitation for Manipulating the Control Block Bits
Do not manipulate the MSG instruction control block values except
as noted below. For example, do not clear the first word of the
control block, do not unlatch the time-out control bit, and so on.
The only MSG instruction control bits that may be manipulated by
the ladder program without adversely affecting the operation of the
instruction are the CO, EN, and TO bits. The enable bit
(EN = bit 15) may be unlatched, but only when the done bit
(DN = bit 13) or error bit (ER = bit 12) has been set, indicating the
successful or unsuccessful completion of the previous message.
In addition, when a MSG is in progress and the ladder program
wishes to terminate it for any reason, this may be done by enabling
the time-out bit (TO = bit 8). The next time the processor scans the
MSG instruction with the TO bit set, it will error the MSG (ER = 1).
The MSG instruction may then be re-enabled with a false-to-true
transition on the next program scan.
MSG Instruction