One Shots

that does just that:[SIZE=-1]

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• [FONT=Arial, Helvetica, sans-serif][SIZE=-1]Rung 1-When NO (normally open) input 0000 becomes true DIFU 1000 becomes true. [/SIZE][/FONT]
• [FONT=Arial, Helvetica, sans-serif][SIZE=-1]Rung 2[/SIZE][/FONT][FONT=Arial, Helvetica, sans-serif][SIZE=-1]- NO 1000 is true, NO 1001 remains false (HOW THIS IS FALSE::IT HAS TO BE TRUE), NC 1001 remains true, NC 1000 turns false. Since we have a true path, (NO 1000 & NC 1001) OUT 1001 becomes true. [/SIZE][/FONT]
• [FONT=Arial, Helvetica, sans-serif][SIZE=-1]Rung 3- NO 1001 is true therefore OUT 500 turns true. [/SIZE][/FONT]

Please explain me this ..this seems to be very confusing...

Its true after the rung has been executed. Not before. Remember, instructions are executed serial, not paraller.

Thanks for your reply. why the instructions are executed in serial not parallel??

I´m not clear what difu is,
if difu is a oneshot, this is a a "toogle" instruction.

ason said:

I´m not clear what difu is,
if difu is a oneshot, this is a a "toogle" instruction.

Click to expand...

You are right. DIFU is differentiate up. Atleast used in omron with that name.

Yes, this is a toggle, but a perfect illustration of how not to write programs.
The vertical link in the middle of the branches is fully redundant and confusing.
Remove it and swap the contacts in the bottom branch, for better understanding of the logics.
This will be a classic toggle.

Here is how I do a toggle in Omron - the input is a DIFU as shown by the up arrow. This is available in all the latest PLCs. It is really simple.

BobB said:

Here is how I do a toggle in Omron - the input is a DIFU as shown by the up arrow. This is available in all the latest PLCs. It is really simple.

Click to expand...

The solution is specific for Omron, like the ALT instruction specific for Mitsubishi, while the contacts and coil solution is platform-independent.

By the way, the Always On contact in your fragment is also totally redundant.

There is a very good reason for the always on contact. If it is desirable to disable a rung during commissioning (often is) just put a / through the always on contact and the rung is disabled. Also, if all contacts come straight off the left hand side rail and it becomes necessary to insert a single contact to drive the rung one has to redraw the left hand side of the rung. With the always on contact there it is really easy to move the whole lot right to insert a contact without having to draw vertical lines and delete segments of horizontal lines - too time consuming and annoying. Easier to use the always on contact in case!!