Mitsubishi Electronics FX1S manual How STL Operates, Each step is a program, Look Inside an STL

FX Series Programmable Controllers STL Programming 3

3.2How STL Operates

As previously mentioned, STL is a system which allows the user to write a program which functions in much the same way as a flow chart, this can be seen in the diagram opposite.

STL derives its strength by organizing a larger program into smaller more manageable parts. Each of these parts can be referred to as either a state or a step. To help identify the states, each is given a unique identification number. These numbers are taken from the state relay devices (see page 4-6 for more details).

M8002

S 0

X0

X1

S 22

T0

S 27

T7

X0

X1

S 26

X15

3.2.1Each step is a program

Each state is completely isolated from all other states within the whole program. A good way to envisage this, is that each state is a separate program and the user puts each of those programs together in the order that they require to perform their task. Immediately this means that states can be reused many times and in different orders. This saves on programming time AND cuts down on the number of programming errors encountered.

A Look Inside an STL

On initial inspection the STL program looks as if it is a rather basic flow diagram. But to find out what is really happening the STL state needs to be put ‘under a microscope’ so to speak. When a single state is examined in more detail, the sub-program can be viewed.

With the exception of the STL instruction, it will be immediately seen that the STL sub-program looks just like ordinary programming.

￿The STL instruction is shown as a ‘fat’ normally open contact.

All programming after an STL instruction is only active when the associated state coil is active.

￿The transition condition is also written using standard programming.

This idea re-enforces the concept that STL is really a method of sequencing a series of events or as mentioned earlier ‘of joining lots of smaller programs together’.

	2
	S 22
	T0
	1
STL	2
	Y22
S 22
	K20
	T0
	T0
	SET S 27
	1

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