Filter
Top Products
6 Step Ladder Instructions
6.1 Step Ladder
92
FXCPU Structured Programming Manual
[Basic & Applied Instruction]
6. Step Ladder Instructions
6.1 Step Ladder
This chapter introduces the instructions of structured project that correspond to the MELSEC-LD step ladder
instructions.
6.1.1 Outline
In programs using step ladder instructions, a state relay S is assigned to each process based on machine
operations, and input condition and output control are programmed as sequences connected to the state
output.
6.1.2 Function and operation explanation
In step ladder program, a state S is regarded as one control process, and a sequence of input condition and
output control are programmed in a state relay.
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.
1. Operation of instruction
In a step ladder program, each process performed by the machine is expressed by a state relay.
A state relay consists of a drive coil and contact (STL output) in the same way as other relays.
Use SET or OUT instruction to drive a coil, and use STL instruction for a contact.
• When a state relay turns ON, a connected circuit (internal circuit) is activated by way of an STL output.
When a state relay turns OFF, a connected internal circuit is deactivated by way of an STL output.
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 transfer process, the both state relays are ON only instantaneously (during one operation
cycle).
In the next operation cycle after the ON status was transferred the former state is reset to OFF.
When the transfer state relay S is used in a contact instruction, however, the contact image is executed in
the OFF status immediately after the transfer condition is satisfied.
• One state relay number can be used only once.