Rockwell Automation 1747-DCM,D17476.8 Direct Communication Module - Manual (Page 49)

Chapter 6
Programming
6–7
You can use the status bits in your ladder logic to monitor various conditions
of the remote processor and the RIO network. Some examples for using the
status word bits are given here. Each of the examples shows how ladder
logic rungs could be programmed in the SLC processor to respond to the
condition of a status bit from the RIO scanner.
Important: The application examples assume the portion of the scanner
image assigned to the DCM is logical rack 2, starting group 0, 1
full rack, and is located in SLC physical slot 3.
RIO Scanner Status Word
Using the Program/Test/Fault Mode Bit
When the RIO scanner’s supervisory processor is in Program, Test, or Fault
Mode, its outputs are automatically inhibited (reset off) unless Hold Last
State is used. However, outputs sent to the DCM (DCM inputs) are not
automatically inhibited. If you want to inhibit any one SLC output
controlled by a DCM input, you can use an Examine If Open (XIO)
instruction addressed to the Program/Test/Fault Mode bit (I:3.0/9 in the
example below). This assumes an SLC output is being driven by an input
(I:3.1/0) from the scanner to the DCM, as shown below.
] [
I:3.1
00
]/[
I:3.0
09
( )
O:1.0
00
SLC Rung
to Monitor
RIO Scanner Status Bit 09
DCM Conditional Program/Test/Fault SLC
Output Status Bit Input
If you want to clear the DCM’s entire input image (data from the RIO
scanner when the RIO scanner’s supervisory processor is in Program/Test/
Fault Mode), you can set the DCM Clear On Fault DIP switch to the OFF
position. Please refer to chapter 4, Module Configuration, for more
information on this DIP switch.
DCM/SLC Output Status Word
Using the Data Invalid Bit
Whenever the distributed SLC leaves Program/Test/Fault Mode and enters
Run Mode, there is a time period after the Program/Test/Fault Mode bit is
cleared when the data sent from the DCM/SLC to the RIO scanner is invalid.
For this reason, the Program/Test/Fault Mode bit should not be used by the
RIO scanner’s supervisory processor to determine the validity of data sent
from the DCM. Instead, both processors’ programs should use the DCM
output Data Invalid bit (12 octal).
Applications Using I/O Status
Word Bits