Ladder Logic help
- Thread starter JCannon
- Start date
- Status
frizbeedog
Senior Member
- Location
- Oregon
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
081116-1245 EST
JCannon:
If you associate a closed contact with the logical state TRUE or 1, and an open contact with FALSE or 0, then the truth tables for two inputs and one output are:
The AND and OR functions can be expanded to more than two inputs. XOR can not be for there is no logical definition for more than two inputs.
The AND function requires all inputs to be TRUE to produce a TRUE output. A normal OR produces a TRUE output if any one or more inputs are TRUE.
In this circuit output Q will be true if both A and B are true, OR if C alone is true, OR if A, B, and C are true.
Make C equal to Q and when both A and B are true, then Q will be true. Make either or both A and B false and Q remains TRUE and will never change state. This is the basis of a holding circuit. You figure out how to drop it out after both A and B become FALSE, but not if only one of A or B becomes FALSE.
If you made C only parallel with A, then the logic would require B = TRUE in combination with either A or C being TRUE for Q to be TRUE. In this circuit if C = Q, then B can be used to dropout Q.
.
JCannon:
If you associate a closed contact with the logical state TRUE or 1, and an open contact with FALSE or 0, then the truth tables for two inputs and one output are:
Code:
Logical AND
A B Output
0 0 0
0 1 0
1 0 0
1 1 1
Logical OR
A B Output
0 0 0
0 1 1
1 0 1
1 1 1
Logical XOR (exclusive OR) (part of what is required for a binary adder)
A B Output
0 0 0
0 1 1
1 0 1
1 1 0
Logical NOT (generated by using a normally closed contact on a relay)
A Output
0 1
1 0
Code:
Logical NAND
A B Output
0 0 1
0 1 1
1 0 1
1 1 0
Logical NOR
A B Output
0 0 1
0 1 0
1 0 0
1 1 0
Logical NXOR ( NOT exclusive OR)
A B Output
0 0 1
0 1 0
1 0 0
1 1 1The AND and OR functions can be expanded to more than two inputs. XOR can not be for there is no logical definition for more than two inputs.
The AND function requires all inputs to be TRUE to produce a TRUE output. A normal OR produces a TRUE output if any one or more inputs are TRUE.
Code:
A B Q
---------| |-------| |---------------[output]
|
C |
---------| |-----------------In this circuit output Q will be true if both A and B are true, OR if C alone is true, OR if A, B, and C are true.
Make C equal to Q and when both A and B are true, then Q will be true. Make either or both A and B false and Q remains TRUE and will never change state. This is the basis of a holding circuit. You figure out how to drop it out after both A and B become FALSE, but not if only one of A or B becomes FALSE.
Code:
A B Q
---------| |-------| |---------------[output]
|
C |
---------| |---If you made C only parallel with A, then the logic would require B = TRUE in combination with either A or C being TRUE for Q to be TRUE. In this circuit if C = Q, then B can be used to dropout Q.
.
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