Omron NJ501-1500

2-15
2 Instruction Descriptions
NJ-series Instructions Reference Manual (W502)
Ladder Diagram Instructions
2
LD and LDN
If you specify upward or downward differentiation, the operation depends on the following: the value of
the variable the last time the instruction was executed and the current value of the variable. This is
shown below.
The following figure shows a programming example and timing chart.
• An error occurs in the following case and the output value from the last execution is retained.
• You specify an array element for the variable value and the element does not exist.
Example: A BOOL array a[0..5] is defined, but the instruction is executed using a[10] as the vari-
able.
• Do not use these instructions as the rightmost instruction on a rung. If you do, an error occurs on the
Sysmac Studio and you cannot transfer the user program to the Controller.
Instruction
Differentiation specifi-
cation
Value of variable at last execution and current
value of variable
Output value
LD
Upward differentiation
FALSE at the last execution → Currently TRUE TRUE
Other than the above. FALSE
Downward differentia-
tion
TRUE at the last execution → Currently FALSE TRUE
Other than the above. FALSE
LDN
Upward differentiation
FALSE at the last execution → Currently TRUE FALSE
Other than the above. TRUE
Downward differentia-
tion
TRUE at the last execution → Currently FALSE FALSE
Other than the above. TRUE
Precautions for Correct Use
Instruction execution
A
A
A
A
A
A
B1
B2
B3
B4
B5
B6
A
B1
B2
B3
B4
B5
B6
↑
↑
↑
↑
TRUE
FALSE
TRUE
FALSE
TRUE
FALSE
TRUE
FALSE
TRUE
FALSE
TRUE
FALSE
TRUE
FALSE