Alright, I just wrote an E-mail to my professor asking for some help in his class. I think that the E-mail is the best thing to sum up what I've been going through for the past week (and sort of the whole semester), so I'll just paste parts the E-mail here...
For every single project that I have done in this class, I end up spending huge amounts of time staring at my circuit simulation, trying to debug it. For this most recent project, I finished my paperwork on Sunday night. All of my equations were derived, my init logic was ready, I had determined what chips I was going to use, and I had even created a C++ program to make sure that my equations were correct. On Tuesday, I start working on my Logic Works simulation. Tuesday night, I completed the diagram...or so I thought.
It just won't work! Here's my init logic... When yp is a preset state of y, and yn is the next, yn = init' * yp. This equates to yn = init NOR yp', which is what I implimented in my circuit. My equations should be stable at state 000/00... You would think that when init = 1, yn would be set to 0 because 0*x=0, but it doesn't! For some off-the-wall reason, my variables jump straight to 1 right after the initialization. I checked and double checked my diagram, and nothing appeared to be wrong... everything is two-level, I've checked for hazards in my equations, I've checked to make sure the right wires are connected to the right equations, I've double checked to make sure that I didn't somehow make my equation 3 levels instead of 2 (not counting init)... I've tried EVERYTHING!
Alright, so this at about midnight this morning I decide to start from scratch. I create a whole new logic works diagram, and this time I use normal logic gates instead of the 7400 Actual library. I set the delays of the gates to 22, and no dice. I set it to 1, no dice. I set it to 0 just to make sure that it's not a hazard that's screwing me up, and no dice! At this point, shouldn't my circuit replicate the C++ program that I made? Well, it doesn't.
All the while that I'm staring at these Logic Works diagrams, I am tempted to just wire it and see what happens, but I'm afraid that it will just end up being a waste of 4 hours or so, so I don't do it.
Professor Thweatt, the problem is that it's not just this project that I have had trouble with. Every single project that I have done, the same thing happens. The past two projects that I have not turned in, I have "complete" Logic Works diagrams for, but I did not finish the project. The point is that I need your help. I need to meet with you, I need to show you exactly what I've done on my project, and I need you to show me exactly what the heck I did wrong. I cannot figure it out by myself, and none of the graded reports that I have been handed back help me figure it out, either. I hope that you can help me.
Would you please be willing to take a little extra time to help me with my problem? I am afraid that this will take a little longer than a normal office-hours visit, so I do not want to interfere if other people want to see you as well. Can we set up an appointment? I would so greatly appreciate it! I look forward to hearing your reply. Thanks in advance.
Sincerely,
Adam Russell
PS. I forgot to mention...I've already turned the project in. It is not validated, it is not wired, and the simulation is incorrect. However, a bad grade is better than none, and I know that I will not be able to fix it on my own. I'm not looking for an "easy" (haha) A on the project. I just want to know what I did wrong.
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