Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 109

Precautions
• The step operation is almost the same as the following circuit.
(1)Input condition of each instruction
(2)Contact (on when active, off when inactive) indicating the step status
• If the CALL instruction is used to issue a subroutine call in an action of the step, the output of the call destination is not
turned off even when the step becomes inactive after the transition becomes TRUE. To turn off the output of the call
destination when the step becomes inactive after the transition becomes TRUE, write the FCALL instruction after the CALL
instruction or use the XCALL instruction. When using a subroutine call in an action of the step, using the XCALL instruction
can reduce the number of steps.
• Even when the input condition in the action is always on, it is assumed to be off when the action is inactive. Therefore,
immediately after the step becomes active, the instruction is executed when the output is turned on. For example, when the
input condition is set to be always on by using the instructions executed at the rising edge such as the PLS or INCP
instruction, the instruction is executed every time the step becomes active.
• The device that turned on by the OUT C instruction, the SET instruction, a basic instruction, or an application instruction in
the action is not turned off even when the step is deactivated and the action is ended. To turn off the device, execute the
RST instruction separately.
• With the PLS or PLF instruction, the specified device is normally turned on for only one scan and thereafter becomes off.
However, the specified device holds the ON state if it is turned on at the same time when the transition of the coil HOLD
step [SC] becomes TRUE. In this case, it is turned off by changing the condition to the one where the coil output of the coil
HOLD step [SC] turns off or activating the step again. For the conditions where the coil output turns off, refer to the
following.
Page 97 Timing of when coil output turns off
• If the step is deactivated and the action is ended while the input condition of the PLF instruction is on, the specified device
remains on.
• When the transition becomes TRUE in the coil HOLD step [SC] or the step is stopped by SM325 (Output mode at block
stop) which is set to hold, operation may not be performed just holding the coil output. This case means the non-execution
status, and therefore the operation of each instruction at the time of operation resumption depends on the execution
condition before the no-execution status is entered.
• When a program which cannot be described in MELSAP-L (instruction format) is created in detailed expression in ladder
diagrams and switched to MELSAP-L (instruction format), the program will be displayed "????????". When the definition of
the label used in a program is deleted, the program will be also displayed in the same way. To check and modify the
program, switch to detailed expression.
• When a program which has been created in MELSAP-L (instruction format) is switched to detailed expression in ladder
diagrams, a contact SM400 (Always ON) will be added as an execution condition of an instruction.
MELSAP-L (instruction format)
(1)
(2)
(1)
Detailed expression in ladder diagrams
Action
8 SFC PROGRAM
107
8.2 Structure
8