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Basics of PLC Programming - Coggle Diagram
Basics of PLC Programming
Processor Memory Organization
Program Files
Subroutine Files
Interrupt Files
Main Ladder Program
Data Files
Input Data File
Output Data File
Internal Data Files
Program Scan
Program Execution
Solves ladder logic
Evaluates each rung left to right
Determines logical continuity
Output Scan
Updates output image table
Transfers data to output terminals
Energizes/de-energizes devices
Input Scan
Updates input image table
Converts electrical signals to binary
Reads physical input signals
PLC Programming Languages
Ladder Diagram
Based on relay logic
Most commonly used
Graphical representation
Other Languages
Function Block Diagram (FBD)
Structured Text (ST)
Instruction List (IL)
Language Selection Factors
Manufacturer support
Application type
User familiarity
Relay-Type Instructions
Input Instructions
Examine If Closed (XIC)
Examine If Open (XIO)
Test input conditions
Operation Characteristics
Based on Boolean logic
TRUE = 1, FALSE = 0
Controls logical continuity
Output Instructions
Controls field devices
Non-retentive
Output Energize (OTE)
Instruction Addressing
Address Format
Word number
Bit number
Slot number
I/O Addressing
Rack/slot configuration
Physical I/O modules
Terminal mapping
Internal Addressing
Timers (T)
Counters (C)
Internal bits (B)
Branch Instructions
Nested Branches
Branch within branch
Complex logic implementation
Used in advanced control
Branch Rules
Proper alignment required
Logical continuity maintained
Must follow ladder syntax
Parallel Branches
Multiple input paths
True if any branch is true
Logical OR condition
Internal Relay Instructions
Internal Contacts
Represent internal bits
Used across program
Reduce wiring complexity
Applications
Status indication
Interlocking circuits
Sequence control
Internal Coils
Used for memory
Control logic flow
No physical output
Examine If Closed (XIC) and Examine If Open (XIO)
Examine If Open (XIO)
TRUE when bit = 0
Equivalent to normally closed contact
Used for fault logic
Practical Usage
Safety logic
Interlocks
Start/Stop circuits
Examine If Closed (XIC)
Equivalent to normally open contact
Used for active signals
TRUE when bit = 1
Entering the Ladder Diagram
Program Entry Steps
Insert instructions
Verify logic
Define I/O addresses
Programming Devices
Industrial terminals
PC-based software
Handheld programmers
Monitoring and Editing
Forcing I/O
Real-time debugging
Online editing
Modes of Operation
Run Mode
Executes program
Controls outputs
No editing allowed
Test Mode
Program runs
Outputs disabled or limited
Used for troubleshooting
Program Mode
Outputs disabled
Safe configuration mode
Editing allowed