Rockwell Automation 2755-SNx Adaptascan Bar Code Readers - Manual (Page 241)

12–20 Communicating with a PLC-5 Processor on a DeviceNet Network using Explicit Messaging
Publication 2755-6.8
Explicit Message Program Control Feature
DeviceNet
drop line
DeviceNet trunk line
Master’s Explicit
Request
Slave’s Explicit
Response
1203-GK5
Communication
Adapter
Block Transfer Write file (64 words)
(sent from processor to scanner module)
Block Transfer Read file (64 words)
(sent from scanner module to processor)
Explicit Message – A message used to transmit
commands, data, requests for data or
responses. The message is sent from a client
on the DeviceNet network to a server on that
network.
Request – An explicit message sent by a client
to a server requesting the server to perform
a function.
Response – An explicit message sent by a
server to a client in response to the client’s
request. For every request issued, there is a
response.
4
1305 AC
drive
5
Block Transfer Read file
is completed. TXID’s
are deleted and can be
reused.
AdaptaScan
Bar Code
Reader
1. Format a Block Transfer Write file in the processor to send an
Explicit Message Request to the scanner module (download).
2. The scanner module transmits the Explicit Message Request to
the slave device over the DeviceNet network.
3. The slave device transmits the Explicit Message Response back
to the scanner and is queued into a block transfer buffer.
4. The processor uses a Block Transfer Read file to retrieve the
Explicit Message Response from the scanner’s buffer (upload).
5. The Block Transfer Read file is completed. The transaction IDs
are deleted and can be reused.
The scanner module requires a precisely-formatted block transfer
read and write size of 64 words. The Explicit Message Control table
in the scanner module is 64 words. The scanner module uses the
block transfer size as an indicator that the content is a client/server
request.