8 APPLICATION INSTRUCTION
8.19 Initial State
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8
• 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.
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.)
Special relay
Description
Remarks
SM8040
(STL transfer disable)
When this special relay turns ON, transfer of every state is disabled.
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.
Special relays
automatically controlled
by the IST instruction
SM8041
(Transfer start)
This special relay allows transfer from the initial state S2 to the next state.
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
(Start pulse)
SM8042 is activated instantaneously only when the start button is pressed.
SM8047
(Enable STL monitoring)
When IST instruction is executed, SM8047 is set to ON.
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
(Zero return complete)
Set this special relay (SM) to ON by a user program when the machine returns to the zero point in
the zero return operation mode.
Special relays controlled
by a sequence program
SM8044
(Zero point condition)
Detect the zero point condition of the machine, and drive this special relay. This signal is effective
in every mode.
SM8045
(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 SM8045 has been set to ON in advance, however, only operation state relays are
reset.
X4
X2
SM8044
IST
X20
S20
S27
SM8000
Y1
Left limit Upper
limit
Unclamping
Detects that the machine is located at the zero point, and
regards it as the condition to start the automatic mode.
RUN monitor
Zero point condition
Initial state
Summary of Contents for MELSEC iQ-F FX5
Page 1: ...MELSEC iQ F FX5 Programming Manual Instructions Standard Functions Function Blocks ...
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Page 17: ...15 CONTENTS ...
Page 24: ...22 MEMO ...
Page 1050: ...1048 26 TIME DATA FUNCTIONS 26 4 Division MEMO ...
Page 1068: ...1066 29 COUNTER FUNCTION BLOCKS 29 4 Counter Function Block Operation error There is no error ...
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