Installation manual

Publication 1747-RM001G-EN-P - November 2008
Application Example Programs G-19
In this case, the good read output is turned on as soon as a valid read occurs,
and the no-read output is turned on after the decoder has attempted to read a
label for a specified amount of time and could not.
The amount of time the decoder attempts to read a label is variable and is
called the “No-Read Timer”. For this example it is assumed that the product is
moving by the scanner and if the label is not read in 2 seconds, it is not read at
all. Therefore, the “No-Read Timer” parameter in the bar code decoder is set
to 2 seconds. Refer to the DS/DD Series Enhanced Bar Code Decoders
(Bulletin 2755) User’s Manual, publication 2755-833, for details concerning the
configuration of your Allen-Bradley Enhanced Bar Code Decoder.
Operating Sequence
With the bar code decoder configured as previously described, the following
series of event take place when a product with a good bar code label breaks the
photo switch and this input to the SLC goes from false-to-true. The SLC 5/03
ladder program logic to make it happen is also included. Please note that, as
previously stated, a bar code/SLC system may be configured in a variety of
ways.
Messages sent by the SLC processor to the Enhanced Bar Code Decoder must
be programmed as shown by the example ladder program on page H-29. If
this logic is not followed, the communication between the two DH-485
devices could become out of sequence, resulting in no data transfers between
the decode and the SLC processor. To correct such a problem, cycle power to
the decoder.
Table G.2 Result of Scanning a Valid Bar code
Result of Scan Bar Code Decoder Response Processor Response
Good Read turns on its “Good Read” onboard
output wired to the SLC processor
When one of these two inputs
to the SLC are turned on, the
SLC will initiate a “MSG Read”
to the decoder to get the label
data or no-read message data.
No-Read turns on its “No-Read” onboard
output wired to the SLC processor