Rockwell Automation 2755-SNx Adaptascan Bar Code Readers - Manual (Page 225)

12–4 Communicating with a PLC-5 Processor on a DeviceNet Network using Explicit Messaging
Publication 2755-6.8
Message Flow Control
DeviceNet Input #8 and Output #16 control the transmission of bar
code messages when using DeviceNet master-slave. Message flow
control (handshaking) lets the controller know that data is available
and that the reader does not send out messages faster than they can
be received. Your controller logic program must transfer the
message data and set the DeviceNet Input #8 (Send Next Data) for
message flow control.
New Data
Is indicated by changing the state of DeviceNet Output #16 of the
DeviceNet I/O. A change of state (0 to 1 or 1 to 0) indicates that a
new message is being sent.
Send Next Data
Is indicated by changing the state of DeviceNet Input #8 of the
DeviceNet I/O. A change of state (0 to 1 or 1 to 0) indicates that the
controller is ready to receive the next message.
Flow Control Example
The following shows how DeviceNet Input #8 and Output #16
control the transmission of messages. Output #16 is changed by the
reader and Input #8 is changed by the controller.
DeviceNet Scan Number Message Data DeviceNet
Output #16
DeviceNet
Input #8
1 - Poll - OFF (0)
1 - Response No Message Sent OFF (0)
2 - Poll - ON (1)
2 - Response Message 1 Sent ON (1)
3 - Poll - OFF (0)
3 - Response Message 2 Sent OFF (0)