A FIG. Understand the workings of a PLC

PLC works

it is well known that the PLC works as follows:

circulation scanning: from the head end to the end end of the program, from left to right side, progressive scan, again and again!

a line looks very simple, also is easy to understand, but in the actual programming errors, this is because the foundation is not solid. The cycle of the PLC scan specific is how it works? We can refer to a binary frequency circuit is introduced. Binary frequency circuit

what is binary frequency circuit, a simple example:

the lighting and extinguishing of a button in a light bulb, first press the button, the light bulb, the second bulb out, press the button that is binary frequency circuit!

binary frequency circuit implementation are many ways, in order to better reflect the theme of this issue, The PLC works) , will use the basic logic instruction to write, detail see below; Among them: button - — X0, light - — Y0。

PLC cycle scanning process

words, more detailed than a picture:

don't understand it doesn't matter, here are isolations

the following four figure to explain, first press the button to release

- — Lights up.

figure 1, the button before the program status

figure 2, button, PLC of the first scan cycle

figure 3, button, ( Haven't loosen) Second, PLC scan cycle ( Hypothesis is the second, scanning cycle quickly)

figure 4, after the release of program state

the following four figure to explain, second press the button to release process

- — Lights go out.

figure 1, the second press the button before the program status

figure 2 second, button press, PLC controller of the first scan cycle

figure 3, button according to the end, for the second time, Haven't loosen) Second, PLC scan cycle

figure 4, after the release of program state

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