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FX3S/FX3G/FX3GC/FX3U/FX3UC Series
Programming Manual - Basic & Applied Instruction Edition
14 Handy Instruction – FNC 60 to FNC 69
14.1 FNC 60 – IST / Initial State
4. Special auxiliary relay (M) for the IST instruction
Auxiliary relays (M) used in the IST instruction are classified into two types. Some auxiliary relays are automatically
controlled by the IST instruction itself according to the situation. Other auxiliary relays should be controlled by a
program for preparation of operation or for purpose of control.
1) Special auxiliary relays automatically controlled by the IST instruction
a) M8040: STL transfer disable
When this special auxiliary relay turns ON, transfer of every state is disabled.
Individual operation mode:
M8040 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:
M8040 is always effective except when the start button is pressed. When the start button is pressed,
M8040 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.
b) M8041: Transfer start
This special auxiliary relay allows transfer from the initial state S2 to the next state.
Individual operation mode and zero return operation mode:
M8041 is not effective.
Stepping operation mode and cycle operation mode:
M8041 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.
c) M8042: Start pulse
M8042 is activated instantaneously only when the start button is pressed.
d) M8047: Enable STL monitoring
When IST instruction is executed, M8047 is set to ON.
When the M8047 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 data register D8040 to D8047.
Up to eight state relay numbers in the ON status can be monitored.
If either state relay is ON, the special auxiliary relay M8046 is set to ON.
2) Auxiliary relays controlled by a sequence program
→ For details on these controls, refer to the next page.
a) M8043: Zero return complete
Set this special auxiliary relay (M) to ON by a user program when the machine returns to the zero point in the
zero return operation mode.
b) M8044: Zero point condition
Detect the zero point condition of the machine, and drive this special auxiliary relay. This signal is effective in
every mode.
c) M8045: All output reset disable
When the mode is switched among individual operation mode, zero return operation mode and automatic
mode, all outputs and operation state relays are reset if the machine is not located at the zero point.
If M8045 has been set to ON in advance, however, only operation state relays are reset.