Honeywell PLC ML-200R Instruction Basics
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This document provides an overview of basic data types, variables, and program types in PLC programming. It defines basic data types and shows a data type hierarchy chart. It describes two ways that variables can be expressed and notes that variables must have unique identifiers. It then explains the differences between functions, function blocks, and programs. Functions have one output, no internal state, and cannot use direct variables or call other programs. Function blocks can have multiple outputs, internal state, and can use direct variables or call programs. Programs are like function blocks but cannot be called by other programs or function blocks.
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Honeywell PLC ML-200R Instruction Basics
- 1. ML- 200 Basic of Instruction List SHIVAM SINGH PROJECT ENGINEER +91-8527199116 [email protected]
- 2. Data Type- Basic Data Type-
- 3. Data Type……
- 5. Data Type Hierarchy Chart-
- 13. Variable- A variable has its own value and refers to data used in a program. ‘Variable’refers to something that can vary such as an input/output of PLC, memory, etc. Variable Expression Variables can be expressed in two ways: by giving a name to a data element using an identifier (Variable by Identifier) or by directly assigning a memory address or an input/output of PLC to a data element (Direct Variable). A variable by identifier must be unique within its ‘effective scope’ (program area where the variable was declared) in order to distinguish it from other variables. A direct variable is expressed as one, which starts with the percentage sign (%) followed by the ‘location prefix’, a prefix of the data size, and more than one unsigned integer divided by a period (.).
- 15. Variable…..
- 16. Program Type- Function A function has one output and does not have any data with status in it. That is, to be a function, consistent input must yield consistent output. An internal variable of a function cannot have an initial value. Users can't declare a function as VAR_EXTERNAL and use it. Use of direct variables inside the function is not allowed. A function is called by program elements and used. Data transfer from program composition elements which call the function, to the function, is executed through an input of a function. A function block or a program cannot be called from inside a function.
- 17. Program Type……. Function Block A function block can have several outputs. A function block has data inside. A function block must declare the instance as it declares variables before using them. Instance is a set of variables used in a function block. A function block must have its data memory to preserve the output value as well as variables used inside, which is called as “instance.” A program is a kind of a function block and also needs to declare “instance.” However, users cannot call a program inside a program or a function block for use, contrary to a function block.
- 18. Program Type….. Users can declare a direct variable inside a function block, and moreover, users can use a direct variable declared as Global Variable and allocated according to ‘Assign (AT)’after declaring it as VAR_EXTERNAL. Calling a program inside the function block is not allowed. Program Users can use a program after declaring an instance like a function block. Use of direct variables in the program is allowed. A program does not have input/output variables. A program can call functions or function blocks.