AutomationDirect DL205 - CPU Control Instructions

DL205 User Manual, 4th Edition, Rev. D
5-177
Chapter 5: Standard RLL Instructions
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CPU Control Instructions
No Operation (NOP)
The No Operation is an empty (not programmed) memory location.
End (END)
The End instruction marks the termination point of the normal program
scan. An End instruction is required at the end of the main program
body. If the End instruction is omitted, an error will occur and the CPU
will not enter the Run Mode. Data labels, subroutines and interrupt
routines are placed after the End instruction. The End instruction is not
conditional; therefore, no input contact is allowed.
Stop (STOP)
The Stop instruction changes the operational mode of the CPU from
Run to Program (Stop) mode. This instruction is typically used to stop
PLC operation in a shutdown condition such as an I/O module failure.
In the following example, when SP45 comes on indicating an I/O module failure, the CPU will
stop operation and switch to the program mode.
NOP




230
240
250-1
260
DirectSOFT
Handheld Programmer Keystrokes
NOP
SHFT
TMR
N
INST#
O
CV
P
ENT
END




230
240
250-1
260
DirectSOFT
Handheld Programmer Keystrokes
END
SHFT
4
E
TMR
N
3
D
ENT
STOP




230
240
250-1
260
DirectSOFT
Handheld Programmer Keystrokes
STOP
SP45
STR
$
SHFT ENT
STRN
SP
4
E
SHFT
RST
S
MLR
T
INST#
O
CV
P
ENTSHFT
5
F
SP45 will turn on
if there is an I/O
module failure.
DS Used
HPP Used
DS Used
HPP Used
DS Used
HPP Used