Rockwell Automation 1746-FIO4V SLC 500 Fast Analog I/O/ User Manual - Manual (Page 41)

Publication 1746-UM009B-EN-P - September 2007
Write Ladder Logic 41
Clear the Output for Changing Mode or Cycling Power
This example clears analog output channel 0 during the initialization
scan (first processor scan). The first pass bit, S2:1/15, in the Status File
is used to initialize the analog output when you apply power in the
RUN mode or upon setting the processor to the RUN or TEST mode.
This bit goes ON automatically only for the first-pass scan. To clear
another analog output channel, use another rung with a different
MOV destination address. The analog module is in slot 2.
Detect an Out-of-range
Input Analog modules do not provide an input out-of-range signal to the
processor. However, if this feature is critical to a specific application,
you can program the processor to provide this function.
The following program applies to all SLC 500 processors. It uses
comparison instructions (LES and GRT) to check for analog input
values which exceed low and high limits respectively. Whenever this
happens, the program latches a bit that could serve to trigger an alarm
elsewhere in your ladder program. In this example, the input range is
1…5V dc (decimal range of 409…2047).
] [ MOVE
Source
Dest
S2:1/15
0
O:2.0
MOV
MAIN
Turn OFF Alarms
Turn ON Alarm,
Low Limit Exceeded
Turn ON Alarm,
High Limit Exceeded
END
LES
GRT
Remainder of Program
LESS THAN
Source A
Source B
I:1.0
409
GREATER THAN
Source A
Source B
I:1.0
2047
B3/0
(U)
B3/1
(U)
B3/0
(L)
B3/1
(L)