Installation manual

Publication 1747-RM001G-EN-P - November 2008
Application Example Programs G-25
This rung moves the decimal value for the bar code decoder “Read” command into the MSG instruction’s
“Offset” parameter. The programming software does not allow values greater than 255 decimal to be entered
into a MSG control block “Offset” value.
The internal storage bit, B3/2, gives the MSG instruction a false-to-true transition to send the initial command.
The initial reply from an Enhanced Bar Code Decoder will result in MSG DN = 1 and MSG DA = 0. This indicates
that the decoder has received the command, but has not yet formulated a reply. The maximum time delay
needed between sending the initial command and sending a poll to get the reply is 250 ms. In most cases this
delay could be much less (30 ms to 100 ms), depending on the number of features the decoder is configured for.
The internal storage bit, B3/2, holds the MSG instruction true until DN and DA are both set, indicating
completion of the command sent and reply received sequence. When DN is set and DA is reset, unlatching the
MSG EN bit effectively toggles the MSG instruction the same as if the MSG rung were toggled, i.e. rung
conditions made false, then true. The MSG instruction is toggled one time after DN and NOT DA plus some time
delay, to send a final poll to the decoder to get the MSG reply. When the reply is received, the SLC processor
will set DN and DA.