Metrologic IS3480-00 User Manual download pdf (Page 43)

ScanVue5

Mini Kiosk

User Manual

M37574–01T

Industrial Electronic Engineers, Inc.

23-June-2008 Rev T Page 34

ProductInfo Protocol Description

ScanVue5

has an embedded protocol engine that uses TCP/IP to send the UPC

barcode number from the price verifier to the host computer, and return the price and

description information retrieved from the host computers’ database by its resident

application.

ProductInfo is a TCP based, bi–directional message–passing protocol that uses the

same format when moving data in either direction. In normal operation, the client opens

a connection for each request generated, usually a scanned barcode, and keeps it open

until the server instructs the client to close it. The client can also wait for the server to

open a socket thus allowing asynchronous operation.

An optional non-normal mode provides a permanently open socket so the server can

continuously monitor the state of the client. This mode was created specifically for a

customer.

The protocol also sends events marking a change of state (opening or closing) of any of

the four optional front panel switches. These events may be used by the hosts resident

application to control functions or modes within the application, for instance to change

language displayed when a switch is pressed.

An abstract system level diagram showing the relationship between ScanVue5

, the

network and the host computer is shown in Figure 14. The API is shown at both ends of

the network for clarity. In practice, the application to interface the host computer server

to ScanVue5

will reside on the host computer.

In the interest of robustness, both ends accept any message whether defined or not,

invalid or unknown messages are simply discarded. A maximum reasonable message

length may be used as a means to detect implementation bugs that could result in

loss of synchronization. Such errors terminate the connection. If the client detects it,

it may send an error token following re–establishment of the connection in order to log

the error on the server. If the server is able to detect this condition, it can log it directly.

When the server receives a product query from the price verifier, it must respond even if

the message is just to terminate the connection. Following submitting a query, the client

may choose to take an error action if it receives nothing from the server within a defined

timeout period. The server can make capability queries and/or mode changes before,

during, after, or in lieu of sending any response. If the server wishes to space

messages more widely than the client’s default timeout, it must send a ‘Set Mode’

packet to change the timeout; this need only be done once per query, but must be

done on each query.

The client may send capability messages regardless of whether the key name is known

to the server and the server may retain this information. When the server needs to know

the value of one of these capabilities, it can consult this retained information. If it is not

known, a capability query may be sent and the server may wait a moment for a reply to

be received. This reply will asynchronously update the server’s information, and the

value should be found there by a subsequent lookup following the brief interval required

for the client to respond to the query. If it remains undefined, it can be assumed that the

client declined to respond, probably because that capability name is not known to it.

Mode settings allow the server to select between optional behaviors or parameters in the

client. Theoretically, this can work both ways. If the server wants the client to adopt a

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