Mitsubishi Electric MELSEC iQ-F FX5 Programming Manual page 635

• Special relay (SM) used in the IST instruction are classified into two types. Some special relays are automatically controlled
by the IST instruction itself according to the situation. Other special relays should be controlled by a program for
preparation of operation or for purpose of control.
Special relay Description
SM8040 When this special relay turns ON, transfer of every state is disabled.
(STL transfer disable) Individual operation mode: SM8040 is always effective.
Zero return operation mode and cycle operation mode: When the stop button is pressed, the
operation is held until the start button is pressed.
Stepping operation mode: SM8040 is always effective except when the start button is pressed.
When the start button is pressed, SM8040 is not effective and transfer of states is allowed.
Others: The operation is latched when the PLC mode switches from STOP to RUN, and reset when
the start button is pressed. Even in the transfer disabled status, the operation is held for outputs in
the states.
SM8041 This special relay allows transfer from the initial state S2 to the next state.
(Transfer start) Individual operation mode and zero return operation mode: SM8041 is not effective.
Stepping operation mode and cycle operation mode: SM8041 is effective only while the start button
is pressed and held.
Continuous operation mode: The operation is latched when the start button is pressed, and cleared
when the stop button is pressed.
SM8042 SM8042 is activated instantaneously only when the start button is pressed.
(Start pulse)
SM8047 When IST instruction is executed, SM8047 is set to ON.
(Enable STL monitoring) When the SM8047 turns ON, STL monitoring becomes valid, and state relay numbers (S0 to S899)
in the ON status are stored in turn in the ascending order of device number to the special register
SD8040 to SD8047.
Up to eight state relay numbers in the ON status can be monitored.
If either state relay is ON, the special auxiliary relay SM8046 is set to ON.
SM8043 Set this special relay (SM) to ON by a user program when the machine returns to the zero point in
(Zero return complete) the zero return operation mode.
SM8044 Detect the zero point condition of the machine, and drive this special relay. This signal is effective
(Zero point condition) in every mode.
SM8045 When the mode is switched among individual operation mode, zero return operation mode and
(All output reset disable) automatic mode, all outputs and operation state relays are reset if the machine is not located at the
zero point. If SM8045 has been set to ON in advance, however, only operation state relays are
reset.
Program example
• While the machine is operating, the operation mode can be switched arbitrarily (among stepping operation, cycle operation
and continuous operation) in the automatic mode. When the operation mode is switched between the individual operation
mode, zero return operation mode and automatic mode while the machine is operating, all outputs are reset once to assure
safety, after which the following mode becomes valid. (While SM8045 (All output reset disable) is ON, outputs are not reset
at all.)
Detects that the machine is located at the zero point, and
regards it as the condition to start the automatic mode.
X4 X2 Y1
Left limit Upper Unclamping
limit
SM8000
IST X20
RUN monitor
SM8044
Zero point condition
S20 S27 Initial state
Remarks
Special relays
automatically controlled
by the IST instruction
Special relays controlled
by a sequence program
8 APPLICATION INSTRUCTION
8.19 Initial State
8
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