Mitsubishi Electric MELSEC iQ-F FX5 - Page 21

3 PROGRAM ORGANIZATION UNIT (POU)
3.2 Function Block (FB)
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Operation overview
■Macro type function blocks
The program of a macro type function block is loaded by the calling source program according to the execution flow. At the
time of program execution, the loaded program is executed in the same way as the main program.
Use a macro type function block when giving higher priority to the processing speed of the program.
■Subroutine type function blocks
The program of a subroutine type function block is stored in the FB/FUN file and called by the calling source program when
executed.
Use a subroutine type function block to reduce the program size.
You can nest all of function blocks, and functions up to 32 times.
Macro type function blocks
■Calling source
When calling a macro type function block, the calling source loads the call-target program during compilation.
(1) The FB1 program is loaded into the
main program and executed.
(2) FB3 is loaded into the FB1 program.
(3) The FB2 program is loaded into the
main program and executed in the
same way as the FB1 program.
(1) The program is loaded in two or more call
locations.
FB1
FB1_a
FB2
FB2_a
(Program file)
Main program
FB1 program
(1)
FB2 program
Actual structure of
main program
(2)
(3)
FB3 program
Execution flow
FB1
FB1_a
FB3
FB3_a
FB2_a
FB2
(Program file)
Main program
Execution flow
(FB file)
FB1 program
(FB file)
FB3 program
(FB file)
FB2 program
Program block 1 (displayed) Program file
FB1_a
FB1
FB1_b
(1)
FB1
FB1 program
(FB1_a)
FB1 program
(FB1_b)