733
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
34 SFC Program and Step Ladder
34.1 SFC Program
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34. SFC Program and Step Ladder
This chapter explains the programming procedures and sequence operations for the “SFC” and “step ladder”
programming methods in GX Developer.
34.1
SFC Program
34.1.1
Outline
Sequence control using the SFC (sequential function chart) is available in FX PLCs.
In SFC programs, the role of each process and the overall control flow can be expressed easily based on
machine operations, so sequence design is easy. Accordingly, machine operations can be easily transmitted
to any person, and created programs are efficient in maintenance, specifications changes and actions against
problems.
When SFC programs and step ladder instructions are programmed in conformance to the same rules
respectively, they are compatible each other.
As a result, the substantially same contents can be handled in relay ladder charts which are familiar and easy
to understand.
34.1.2
Explanation of function and operation
In SFC programs, a state relay State S is regarded as one control process, and the input condition and output
control sequence are programmed in each process.
Because the preceding process is not performed any more when the program execution proceeds to the next
process, a machine can be controlled using simple sequences for each process.
Operation of state relay State S and driven instruction
In SFC programs, each process performed by the machine is expressed by a state relay.
• When a state relay turns ON, a connected circuit (internal circuit) is activated.
When a state relay turns OFF, a connected internal circuit is deactivated.
After one operation cycle, non-driving of an instruction (jump status) is not available.
• When a condition (transfer condition) provided between state relays is satisfied, the next state relay turns
ON, and the state relay which has been ON so far turns OFF (transfer operation).
In the state relay ON status transfer process, both state relays are ON only instantaneously (during one
operation cycle).
In the next operation cycle after the ON status is transferred, the former state is reset to OFF.
• A state relay number can be used only once.