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Basics of PLC Programming - Coggle Diagram
Basics of PLC Programming
Processor Memory Organization
Memory Structures
Allen-Bradley PLC
Rack-based
Tag-based
Program Files
Stores user ladder logic
System Functions
Reserved
Main Ladder Program
Subroutine Ladder Program
Data Files
Stores information needed to carry out the program
Output
Input
Status
Bit
Timer
Control
Integer
Reserved
Network Communications
Userr-Defined Bits
Program Scan
Start
Input Scan
The status of
external inputs
is written to the
input image table
(file or register)
ProgramScan
Each ladder rung
is scanned and solved
using the date in the
input file. The resulting
logic is written to the
output image table
(file or register)
Output Scan
The output image
date is transferred
to the external output
circuits, turning the
output device
ON or OFF
Housekeeping
Internal checks
on memory, speed
and operation.
Service any
communication
requests
Programming Languages
Ladder Diagrams
a graphical depiction of a process with rungs of logic, similar to the relay ladder logic schemes that were replaced by PLCs
Function Block Diagrams
a graphical depiction of process flow using simple and complex interconnecting blocks
Sequential Function Chart
a graphical depiction of interconnecting steps, actions, and transitions
Instruction List
a low-level, text-based language that uses mnemonic instructions
Structured Text
a high-level, text-based language such as BASIC, C, or PASCAL specifically developed for industrial control applications
Relay-Type Instructions
Instruction Addressing
To complete the entry of a relay-type instruction, you
must assign an address to each instruction
The assignment of an I/O address can be included in
the I/O connection diagram
Branch Instruction
Input branching by formation of parallel branches can
be used in your application program to allow more than
one combination of input conditions