Installation manual

Publication 1747-RM001G-EN-P - November 2008
G-18 Application Example Programs
The only devices capable of polling a slave device on DH-485 are the SLC
5/03 and higher processors. For the SLC 5/03 processors (1747-OS302,
FRN10 or later), polling can be done via channels 0 and 1. For the SLC 5/04
processors (1747-OS401, FRN7 or later), channel 0 supports this capability.
There are many ways to trigger bar code decoders to read a bar code label
when a label is present.
• A package detect switch wired to both an SLC input module and the bar
code decoder
• A package detect switch wired only to an SLC input and an SLC output
then used to trigger the decoder
• Via a software trigger command from the SLC processor
For this example, the software trigger is used. However, the basic principal is
the same for all trigger modes.
System Set Up
In this example, a photo switch is located such that when it detects a product is
in position for the bar code scanner to read a bar code label on the product, a
discrete input to the SLC 5/03 processor is energized.
The 5/03 ladder program then initiates a MSG Write to the decoder to trigger
the decoder to start scanning for a valid bar code label. When the decoder is
scanning for a valid bar code label, it operates as shown below.
SLC 5/03
1747 Chassis
DH-485
1747-AIC
Power
Supply
Photo
Switch
2755-DS/DD
Enhanced Bar Code
Decoder
Host
Port