Please enable JavaScript.
Coggle requires JavaScript to display documents.
PLC Fundamentals of Logic - Coggle Diagram
PLC Fundamentals of Logic
Derived Logic & Combination Gates
Exclusive-OR (XOR) Logic
Logic Rule: Output is HIGH only if the inputs are different (one HIGH, one LOW).
Ladder Logic Circuit: Built using two parallel branches, each containing one NO and one NC contact in series.
Boolean Expression: Represented as Y = A\bar{B} + \bar{A}B
Combinational Logic
Logic-to-Ladder Conversion: Translating complex gate circuits into series-parallel contact arrangements.
Problem Solving: Designing circuits based on specific requirements (e.g., the "2-out-of-3" voting logic).
Gate Interconnection: Feeding the output of one gate into the input of another to solve complex control problems
NOT, NAND, and NOR Gates
NOR Gate: Combines OR with NOT; the output is HIGH only when all inputs are LOW
NAND Gate: Combines AND with NOT; the output is HIGH unless all inputs are HIGH
NOT (Inverter): Reverses the input state; in ladder logic, this is represented by a Normally Closed (NC) contact.
Boolean Algebra & PLC Instructions
Boolean Laws and Rules
Simplification: Using Boolean rules to reduce the number of contacts needed in a ladder program to save memory.
De Morgan’s Laws: Provide a method to convert between NAND/NOR logic and inverted AND/OR logic.
Commutative/Associative Laws: Dictate that the order of variables in OR/AND operations does not change the result.
PLC Bitwise Instructions
Logical NOT: An instruction that inverts every bit within a single word (1s become 0s).
Masking: Using the AND instruction to "hide" or filter specific bits within a data word.
Word-Level Logic: Instructions like AND, OR, and XOR that compare two 16-bit words bit-by-bit.
Logic-Circuit Design
Equation Development: Writing Boolean expressions directly from written control specifications.
Functional Conversion: Converting between relay-type schematics, logic gate diagrams, and Boolean equations.
Truth Tables: Listing all possible input combinations (e.g., $2^4 = 16$ for four inputs) to define circuit behavior.
Binary Concept & Logic Functions
AND Logic Function
Logic Gate: Represented by the AND gate symbol; output is HIGH only if all inputs are HIGH.
Series Connection: In ladder logic, two or more NO contacts must be closed in a single path to energize the output.
Boolean Expression: Mathematically represented as Y =A.B
OR Logic Function
Logic Gate: Represented by the OR gate symbol; output is HIGH if one or more inputs are HIGH.
Boolean Expression: Mathematically represented as Y = A + B.
Parallel Connection: In ladder logic, any one of several parallel branches can energize the output.
The Binary Concept
Data Storage: Uses binary bits grouped into words (16-bit or 32-bit) to represent status and numerical values.
Logic Representation: Relates binary states to physical conditions like open/closed switches
Two-State Systems: Bases all PLC operations on signals being either ON (1) or OFF (0).