Internal System Devices; Function Devices (Fx, Fy, Fd) - Mitsubishi Electric L02SCPU User's Manual And Reference

5.3

Internal System Devices

Internal system devices are provided for system operations. The allocations and sizes of internal system devices are
fixed, and cannot be changed by the user.
5.3.1

Function devices (FX, FY, FD)

Function devices are used in subroutine programs with argument passing. Data are read or written between such
subroutine programs and calling programs, using function devices.
Ex. When FX0, FY1, and FD2 are used in a subroutine program, and if X0, M0, and D0 are specified with a
subroutine program call instruction, the following data passing are proceeded.
• On/Off data of X0  FX0
• On/Off data of FY1  M0
• Data of D0  FD2
[Calling program]
Because a device in each calling program can be determined by using a function device for subroutine programs, the
same subroutine program can be used without considering other calling programs.
(1) Types of function devices
The following three types of function devices are available.
• Function input (FX)
• Function output (FY)
• Function register (FD)
(a) Function input (FX)
The function input is used to pass on/off data to a subroutine program. Bit data specified by a subroutine call
instruction with argument passing are fetched into a subroutine program and they are used for operations. All
bit devices for the CPU module can be used.
(b) Function output (FY)
The function output is used for passing an operation result (on/off data) in a subroutine program to a calling
program. An operation result is stored in the device specified in the subroutine program with argument passing.
All bit devices except for direct devices of the CPU module (DX) and annunciator (F) can be used.
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[Subroutine program]