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Publication 1766-RM001A-EN-P - October 2008
172
Relay-Type (Bit) Instructions
The ONS instruction is a retentive input instruction that triggers an event
to occur one time. After the false-to-true rung transition, the ONS
instruction remains true for one program scan. The output then turns OFF
and remains OFF until the logic preceding the ONS instruction is false
(this re-activates the ONS instruction).
The ONS Storage Bit is the bit address that remembers the rung state from
the previous scan. This bit is used to remember the false-to-true rung
transition.
Addressing Modes and File Types can be used as shown in the following
table:
TIP
The ONS instruction for the MicroLogix 1400 provides the same
functionality as the OSR instruction for the MicroLogix 1000 and SLC 500
controllers.
ONS Instruction Operation
Rung Transition
Storage Bit
Rung State after Execution
false-to-true (one scan)
storage bit is set
true
true-to-true
storage bit remains set
false
true-to-false,
false-to-false
storage bit is cleared
false
ONS Instruction Valid Addressing Modes and File Types
For definitions of the terms used in this table see Using the Instruction Descriptions on page 92.
Parameter
Data Files
Function Files
CS - Com
m
s
IOS - I/O
DLS
-
D
a
ta
L
o
g
Address
Mode
Address Level
O
I
S
B
T,
C
, R
N
F
ST
L
MG, P
D
RI/RIX
PLS
RTC
HSC
PTOX, PW
MX
STI
EII
BH
I
MMI
LCD
Immedia
te
Dir
e
c
t
Indir
e
ct
Bit
Wo
rd
Long W
o
rd
Ele
m
ent
Storage Bit
•
•
•
•
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