Datalogic AccuLazr AL5010, Руководство по линейке продуктов

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190 Appendix D: Networking Guide AccuLazr™ AL5010 Product Line Manual
Network Host Communications
The AL5010 provides a number of options for transmitted bar code to
another computer (typically referred to as the “host”). Additionally, two host
network connections are supported each with different message definition
and formatting. These connections use ports 3001 and 3002 by default, but
these values are modifiable.
TCP/IP Server
Operation as a TCP/IP server is the default configuration for the AL5010. In
this case, for an application to communicate with an AL5010 from a "host
computer", the application should just initiate a simple TCP/IP socket
connection. When a socket connection to the AL5010 is established, the
green AL5010 network LED will be illuminated (unless client/controller mode
is in use in which the LED indicates the status of the inter-AL5010 network
connections).
One issue should be considered when designing such an application: As
with any socket connection, if one side or the other terminates the
connection without properly closing it - the connection can be left open.
For example, if a host computer has initiated a connection to an AL5010 and
the host computer "crashes" - the connection on the AL5010 will remain
open until the AL5010 attempts to send the next message (normally the next
bar code). At this point, the AL5010 will detect the connection from the host
computer has been terminated and clear the connection allowing the host
computer to reconnect.
However, it is possible that the AL5010 might be powered off while a host
connection is active (or if the power is cycled on an intermediate piece of
network equipment such as a hub or a switch). In this case, the AL5010
socket connection will be closed but the host computer may not be aware of
this change. To handle this situation, it may be desirable to implement a
means by which the host computer can test the state of the network
connection.
One option is to periodically send a simple message (e.g., just a null
character or just a single STX character) to the AL5010 verifying the link is
still active.
Another option is for a heartbeat message to be enabled on the AL5010.
This both provides the host computer with a means for determining if the link
has been lost (by lost of the heartbeat) and provides the AL5010 with quicker
determination of lost of communications with the host computer. This is the
recommended approach.
Accu-Sort Systems, Inc. A4-AL5010_Networking_Guide_R20.doc