Rockwell Automation 1771-SDN DeviceNet Scanner Module Installation Instructions - Manual (Page 33)

Publication 1771-IN014B-EN-P - September 2001
DeviceNet Scanner Module Catalog Number 1771-SDN/C 33
Explicit Message Program Control Limitations
•
The processor is always the DeviceNet client and the slave is
always the DeviceNet server.
•
A maximum of ten Explicit Message Request Transaction Blocks
with the execute command can be queued to the scanner
module at any time. For example, five Block Transfer Write files
containing two transactions each, can be performed at any time.
The scanner module receives and deletes any additional
client/server requests with the execute command over the
maximum of ten.
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.
•
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:
•
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.
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