Rockwell Automation 1747-SDN SLC 500 DeviceNet Scanner Module User Manual - Manual (Page 150)

Publication 1747-UM655B-EN-P - June 2007
150 Explicit Message Program Control
As transactions are removed from the queue and response transaction
blocks are returned to the processor, additional transaction blocks can
be issued in their place, as long as the total does not exceed ten.
•
The module supports one transaction block per upload and
download.
•
Request Transaction Blocks can be queued only for slave
devices of the module and must appear in the module’s scanlist.
•
If a slave device is not communicating at the time the module
processes its Request Transaction Block, the module will return
an error status for that transaction.
•
Check documentation of destination device for specifics
concerning services supported and Class Instance Attribute
information. At a minimum, the module supports the following
DeviceNet services in Request Transaction Blocks.
•
All transaction blocks are processed, therefore an unused
transaction block must be left blank.
•
Client/Server commands and requests with transaction IDs that
are in use are ignored by the module.
•
If a slave device returns a DeviceNet error in response to the
request downloaded from the processor, the scanner recognizes
the error as a successful transaction (status code =1).
A failure to respond to the request within the number of retries or
timeout period specified for the Explicit Message Connection is
recognized by the module as an error. The error code is returned in
the status attribute of the transaction header.
Service Name Service Code Example
Get_Attribute_Single 0E hex Upload a single parameter
value from a device
Set_Attribute_Single 10 hex Download a single
parameter value to a device
Get_Attribute_All 01 hex Upload all parameter values
from a device
Set_Attribute_All 02 hex Download all parameter
values to a device