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SECTION 2
Function Block Specifications
This section provides specifications for reference when using function blocks, including specifications on function blocks,
instances, and compatible PLCs, as well as usage precautions and guidelines.
2-1 Function Block Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2-1-1 Function Block Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2-1-2 Function Block Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2-2 Data Types Supported in Function Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2-2-1 Basic Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2-2-2 Derivative Data Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2-3 Instance Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2-3-1 Composition of an Instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2-3-2 Parameter Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
2-3-3 Operating Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2-4 Programming Restrictions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2-4-1 Ladder Programming Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2-4-2 ST Programming Restrictions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2-4-3 Programming Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2-5 Function Block Applications Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2-5-1 Deciding on Variable Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2-5-2 Determining Variable Types
(Inputs, Outputs, In Out, Externals, and Internals). . . . . . . . . . . . . . 57
2-5-3 AT Settings for Internal Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2-5-4 Array Settings for Input-Output Variables and Internal Variables . . 59
2-5-5 Specifying Addresses Allocated to Special I/O Units . . . . . . . . . . . 61
2-5-6 Using Index Registers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2-6 Precautions for Instructions with Operands Specifying the First
or Last of Multiple Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2-7 Instruction Support and Operand Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 68
2-8 CPU Unit Function Block Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2-8-1 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2-8-2 Operation of Timer Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
2-9 Number of Function Block Program Steps and Instance Execution Time . . . 76
2-9-1 Number of Function Block Program Steps. . . . . . . . . . . . . . . . . . . . 76
2-9-2 Function Block Instance Execution Time. . . . . . . . . . . . . . . . . . . . . 77
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