Rockwell Automation 2755-SNx Adaptascan Bar Code Readers - Manual (Page 246)

12–25 Communicating with a PLC-5 Processor on a DeviceNet Network using Explicit Messaging
Publication 2755-6.8
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 scanner module supports two transaction blocks per upload
and download.
•
Request Transaction Blocks can only be queued for slave devices
of the scanner module and must appear in the scanner module’s
scan list.
•
If a slave device is not communicating at the time the scanner
module processes its Request Transaction Block, the scanner
module will return an error status for that transaction.
•
At a minimum, the scanner module supports the following
DeviceNet services in Request Transaction Blocks.
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
•
Continuous Block Transfers of 64 words are not supported.
•
All transaction blocks are processed, therefore, any unused
transaction blocks must be left blank.
•
Client/Server commands and requests with transaction IDs that
are in use are deleted by the scanner 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 scanner module as an error. The error code is
returned in the status attribute of the transaction header.