Publication 1747-RM001G-EN-P - November 2008
12-44 SLC Communication Instructions
Explicit Message
Instruction Overview
The CEM, DEM, and EEM explicit message instructions allow generic
Common Industrial Protocol (CIP) commands to be initiated to devices, such
as drives, communicating on ControlNet, DeviceNet, and EtherNet/IP
networks. Each instruction requires RSLogix 500 version 7.10 or higher
software for programming.
The CEM instruction utilizes the explicit message capability built into the
1747-SCNR ControlNet scanner module, while the DEM instruction utilizes
the explicit message capability built into the 1747-SDN DeviceNet scanner
module. While not adding any additional capability over what already exists in
the scanner modules, the CEM and DEM instructions greatly simplify the
programming, configuration, monitoring, and troubleshooting of explicit
messages on ControlNet and DeviceNet. Unlike I/O configured in the
scanner module’s scan list, which is updated on a continual basis, explicit
messages allow data to be sent and received on an as-needed basis, minimizing
network traffic. For instance, you may only want to write configuration
parameters to a drive once at machine start-up time. The CEM and DEM
instructions can be used with any SLC 5/03, 5/04, or 5/05 processor that is at
OS firmware level Series C, FRN 10 or higher.
The EEM instruction explicit message capability is implemented through the
channel one Ethernet port of the SLC 5/05 processor. It shares the same
queuing and buffering scheme, as well as Ethernet connection resources, that
are used by the MSG instruction. Like the standard MSG instruction, data can
be sent and received on an as-needed basis. Ethernet explicit messages are
useful for communicating with third party EtherNet/IP devices that don’t
understand standard MSG commands, as well as providing access to data in
Allen-Bradley EtherNet/IP devices that isn’t accessible via standard MSG
instruction commands. The EEM instruction can be used with any SLC 5/05
processor at OS firmware level Series C, FRN 10 or higher.
FCH Target Node responded with: Disk file is write protected or otherwise inaccessible (off-line only).
FDH Target Node responded with: Disk file is being used by another application; update not performed (off-line only).
FFH Local communication channel is shut down.
Table 12.17 MSG Instruction Error Codes (Continued)
Error Code Description of Error Condition
TIP
The MSG error code reflects the STS field of the reply to
your MSG instruction.
Codes E0 - EF represent EXT STS codes 0 - F.
Codes F0 - FC represent EXT STS codes 10 - 1C.
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