Function Blocks - Mitsubishi Electric MELSEC Q Series Programming Manual

Function blocks

Functions, function blocks, and operators are used to edit function blocks. Function blocks can be used by calling them from
programs or function blocks. Note that they cannot be called from functions.
Function block
Function blocks can retain the input status since they can store values in internal and output variables. Since they use
retained values for the next processing, they do not always output the same results even with the same input values.
Function blocks can be described in the ST or structured ladder/FBD language.
Instantiation
Function blocks need to be instantiated to be used in programs. ( Page 24 Functions, function blocks, and operators)
Instances are variables representing devices assigned to labels of function blocks. Devices are automatically
assigned when instances are created with local labels.
Function block specifications
■Nesting
• Macro type function block: 5 levels (Ladder diagram: 2 levels)
• Subroutine type function block: 16 levels
A macro type function block can be called from a subroutine type function block.
A subroutine type function block cannot be called from a macro type function block.
■Number of function blocks that can be called from within a function block.
• Macro type function blocks: No limit
• Subroutine type function block: No limit
*1 There is no limit as long as the memory capacity is not exceeded.
*2 There is no limit as long as the upper limit of pointer in the auto device setting (default: 2048) is not exceeded. Note, depending on the
program, that the upper limit is less than usual because the pointer device is used for other than subroutine type function blocks.
4 PROGRAM CONFIGURATION
20
4.2 POUs
Function
Function block
Operator
*1
*2