Rockwell Automation 2755-SNx Adaptascan Bar Code Readers - Manual (Page 334)

17–12 Communicating with PanelView 900
t
Terminals on a DeviceNet Network
Publication 2755-6.8
Client Explicit Messaging
The PanelView can also communicate using explicit messaging,
where the PanelView initiates the connections (Client). Connections
to other devices are created (using tag editor addressing) and use
explicit messages to read and write values to other DeviceNet nodes.
Only Get_Attribute_Single and Set_Attribute_Single commands are
supported.
Output values assigned (addressed) to client objects in the current
screen context (global or current screen) are scanned sequentially
and data is read from the external device using Get_Attribute_Single
requests.
Input values are sent to the external device (using a
Set_Attribute_Single request) when a change of state is detected on
that input.
Notes on Using Client Explicit Messaging:
•
The devices communicating with the PanelView must have a
sufficient number of available connections to support an Explicit
message connection by the PanelView and any other connections
required by the application. This includes a Group 2 Only Slave
owned by a Group 2 Only Client such as a scanner capable of
providing the UCMM service for the slave.
•
Data read/written must be accessible as an externally addressable
DeviceNet attribute with the Get_Attribute_Single /
Set_Attribute_Single commands.
•
Explicit-Client messaging is not designed for high speed
communications and uses lower priority messaging on
DeviceNet. I/O messaging should be used for time critical
applications.
!
ATTENTION: Do not use Client Explicit messaging
with critical control parameters or as an alternative to a
hard wired emergency stop button.
•
The PanelView has only one general purpose explicit message
connection available at a time to an external client device. Be
aware of this limitation when creating applications requiring
multiple explicit message server connections to a PanelView.