736
9 STEP LADDER INSTRUCTIONS
9.1 Starts/Ends Step Ladder
The actual step ladder program is as follows.
• A step ladder program is expressed as a relay ladder, but it can be created according to the machine control flow using
state relays. A state relay consists of a drive coil and contact (STL contact) in the same way as other relays. Use SET or
OUT instructions to drive a coil, and use STL instructions for a contact.
• The table below shows operations of internal circuits connected to the state relays,
• The figure below shows the timing chart of the state relay (internal circuit) activation status.
• Each state relay has three functions, driving a load, specifying a transfer destination and specifying a transfer condition.
Such as the following program, driving a load and then transition processing. In a state relay without any load, the drive
processing is not required.
Internal circuit diagram operation
Execution in the contact ON status
When a state relay turns ON, a connected circuit (internal circuit) is activated with a STL contact.
Execution in the contact OFF status
(for one operation cycle)
When a condition (transfer condition) provided between state relays is satisfied, the next state relay turns ON, and the
state relay which was been ON before hand turns OFF (transfer operation). In the state relay ON status transfer
process, both state relays are ON for one operation cycle.
In the next operation cycle after the ON status is transferred to the next state relay, the former state relay is reset to
OFF. A drive instruction connected to the bus line of the reset state relay is executed in the contact OFF status for one
operation cycle regardless of the actual contact status before the drive instruction.
When the transfer state relay is used in a contact instruction, however, the contact image is executed in the OFF
status immediately after the transfer condition is satisfied.
Non-execution
An instruction is not executed in the contact OFF status after the operation cycle where the instruction was executed
in the contact OFF status (jump status).
SET
S0
X0
SET
S20
STL
S20
STL
S0
SM402
Y21
Y23
X1
SET
S21
STL
S21
Y23
Y21
RETSTL
END
Process of S0
start
Moving
forward
Moving
backward
Process of S20
Process of S21
This range divided by the STL
instruction is called State.
Execution in the contact OFF status
in one operation cycle
Execution in the
contact ON status
Non-execution
(jump status)
Execution
X11
X10
Drive processing
Transfer processing
X0
X1
STL
S20
STL
S21
Y10
Y11
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 1068: ...1066 29 COUNTER FUNCTION BLOCKS 29 4 Counter Function Block Operation error There is no error ...
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