Allen-Bradley 1747-SN - Scanner Operation

3–7Installation and Wiring
Publication 17476.6 - July 1996
Below is a description of the scanner’s operation at power up, run
mode, and when changing from run mode to program or test mode.
At Power Up
At power up, the the scanner’s communication LED (green LED) is
off until the SLC is changed to Run or Test mode.
In Run Mode
During normal scanner operation (SLC in Run mode), the scanner’s
LEDs illuminate as shown below:
FAULT
FAULT LED is of f.
COMM LED is green.
SCANNER
COMM
When Changing From Run Mode
When the SLC processor is changed from Run mode, to Program or
Test mode the following occurs:
• scanner’s COMM LED remains green.
• the scanner continues to read its input devices and send output
data to its RIO adapters.
• the scanner instructs adapters to either clear all outputs or hold
them in their last state (depending on their configuration). Refer
to the user manual included with each RIO device for specific
information relating to the Hold Last State setting.
Important: If you are using Block Transfer (BT) functionality, BTs
may not function on adapters in Hold Last State
settings. Refer to each device’s user manual for
information on BTs and Hold Last State settings.
Scanner Operation