Installation manual

Publication 1747-RM001G-EN-P - November 2008
G-20 Application Example Programs
Sequence of Events
The photo switch input to the SLC goes from false-to-true
The SLC processors send a “trigger” command to the
decoder via a “MSG Write” command.
The decoder immediately replies to the SLC that it has
properly received the command.
The decoder immediately replies to the SLC that it has
properly received the command.
The reply sets the MSG DN bit and clears the MSG DA bit
in the SLC processor.
The reply sets the MSG DN bit and clears the MSG DA bit
in the SLC processor.
The decoder then processes the command and formulates
a reply to the “MSG Read” command with the decoded
label data included in this reply, and places into its output
buffer awaiting a “poll”.
The SLC processor then waits a specified amount of time
and re-enables the same MSG instruction which now
sends the “poll” to the decoder.
The SLC processor waits a specified amount of time, then
re-enables the same “MSG Read” instruction which now
sends the “poll” to the decoder.
The decoder then responds to this “poll” with its reply to
the “trigger” command. The SLC processor then sets the
MSG DN and MSG DA bits.
The decoder then responds to the “poll” command with
its reply to the “MSG Read” command which includes the
bar code label data.
The decoder then reads the bar code label and turns on
the “good read” output wired to the SLC processor.
The SLC processor then sets the MSG DN and MSG DA
bits to signify its receipt of the data.
When this “good read” input to the SLC goes from
false-to-true, the SLC sends a “MSG Read” to the
decoder.
TIP
These events are described in more detail by the
comments listed within the example ladder program
page G-21.