Internal System Devices - Mitsubishi Electric melsec q00ujcpu User Manual

9.3 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.
9.3.1 Function devices (FX, FY, FD)
(1) Definition
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.
When FX0, FY1, and FD2 are used in a subroutine program, and if X0, M0, and D0 are specified with
Example
a subroutine program call instruction, on/off data of X0 and FY1 are passed to FX0 and M0 respectively, and
D0 data are passed to FD2.
[Calling program]
X0
(2) Applications of function devices
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.
(3) 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.
P0
CALL P0 X0 M0 D0
Figure 9.43 Application example of function devices
[Subroutine program]
FX0
MOV FD2
SET FY1
CHAPTER9 DEVICES
R0
RET
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