Need Help With Column "d"

Usually I am the last person to make comments to students about their posts/questions.

First, you did not need to do it twice nor use capital letters to get attention. Take time and read the rules (Look at New Here), some posts, and attempt to use some etiquette.

Second, why do you need help? If you want the answers provided that will not help you, if you can not answer them then you need to study more; this is a very simple assignment.

just to throw a wrench into the works..what kind of PLC..they all scan differently..what happens on a AB wont always be the same on something else...

That being said AB scans left to right does it not?

The "execution model" does matter, but I think that we can safely assume that this is a left-to-right, top-to-bottom solution engine. Even Modicon ladder "networks" were seven rungs long, weren't they ?

In this example, Roger, the address "D" is being set and reset by Latch and Unlatch instructions.

In the third rung, when "C" is true, then "D" is SET.

D is true when the fourth rung is scanned.

In the fifth rung, when "C" is true, then "D" is RESET. At the end of scan, "D" is reset.


When the ladder is scanned and "C" is false, then the "D" register remains in it's last state, because it was set by a Latch instruction, not an ordinary Output instruction.

That also being said, there's a great tutorial available on this site, under the "Learn PLCs" link at the top. If your textbook or lecture aren't clear on SET/RESET or LATCH/UNLATCH type of instructions, that tutorial might give you another perspective.

Good for you for showing some of your work, but as you've probably seen the regulars on this site are not gentle with do-my-homework types. The more you explain about your thought process, the better the help gets.

rogersph - As A is a function of D and you haven't filled in D then all you could have filled in was columns B,C,E for scan 1 and then got stuck.
How did you know what to put for A at the end of scan 1 ?

Thank you, I will explain my though processes in more detail