Archive: 10 posts

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Im thinking of a piece of logic (Can't get it at the moment because i've just fried my brain on a 16 page menu) and i was hoping someone could help. its a micro chip with 2 inputs and 1 output, and If the last input was #1 then the output is on. if the last input was #2 then the output is nothing. it probably has something to do with a selector and a couple of toggle gates, but nothing's coming to mind, any ideas?

2011-02-25 12:59:00 Author: Unknown User

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Uhh... sounds kind of weird but possible I guess. Maybe use an NOT output for Input #2 and use an AND gate: If #1 is activated, #2 is positive because of the NOT, thus there's an output. If #2 is on, the NOT gate makes it negative, causing it to be unusable. Hope that helps!

2011-02-25 13:02:00 Author: iArekusu Posts: 402

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why not just use a 2 output selector and have nothing coming out of Gate 2's output? gate 1 input > output ... Gate 2 input > no output

2011-02-25 13:43:00 Author: Epicurean Dreamer Posts: 224

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You can also use a counter for this, set to a max count of 1. Count input -> Output Reset input -> No output Selector is probably more appropriate though.

2011-02-25 13:56:00 Author: Tygers Posts: 114

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Your problem can be solved with a 2-port selector and two pulse generators. A pulse generator is simply a "count down' timer with a time of 0.1s. Connect the output of the pulse generators to the inputs of the 2-port selector. Then connect your 2 chip inputs to the inputs of the pulse generators and connect one of the outputs of the 2-port selector to your chip output. The 2-port selector output that has no connection is your "off" state. #1---->Pulse Generator----> 2 Port ------> Chip Output #2---->Pulse Generator----> Selector ------> Not Connected (Chip Output is off when active) When one of your chip inputs are activated they will trigger the pulse generator which will set one of the selector outputs to either 1 or 2 (on or off). This solution will still work if one of your inputs is triggered twice (the selector output will not change). It will also work if one of your inputs is still on when the other input is triggered - the selector will only switch when the opposing input is activated. Hope this is useful.

2011-02-25 14:03:00 Author: fluxlasers Posts: 182

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@fluxlasers: You've just simulated the edge-triggered behaviour of a counter by using 2 counters and a selector. If the edge triggered behaviour is what you want, a single counter is far more appropriate. The 2 port selector and counter variants both have their subtleties and each one is arguably more useful than the other in certain situations.... Annoyingly, I always seem to pick the wrong one first

2011-02-25 14:08:00 Author: rtm223 Posts: 6497

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@fluxlasers: You've just simulated the edge-triggered behaviour of a counter by using 2 counters and a selector. If the edge triggered behaviour is what you want, a single counter is far more appropriate. LOL, just after I posted my reply I noticed Tygers' post about using a counter and realised that would be a more efficient method to solve the problem. I tend to use selectors and pulse generators a lot simply because I find it easier to "read" and de-bug logic circuits. I'll certainly consider using the counter method in future. Thanks Tygers & RTM

2011-02-25 14:44:00 Author: fluxlasers Posts: 182

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Thanks guys, very helpful

2011-02-25 16:32:00 Author: Unknown User

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@fluxlasers: You've just simulated the edge-triggered behaviour of a counter by using 2 counters and a selector. If the edge triggered behaviour is what you want, a single counter is far more appropriate. The 2 port selector and counter variants both have their subtleties and each one is arguably more useful than the other in certain situations.... Annoyingly, I always seem to pick the wrong one first For the... less intelligent of us aaround here, could you go into the potential advantages and disadvantages of each? Not me of course but uh.... you know some people might just use a counter in every scenario and might not really understand why the two port superior would ever be the better option.

2011-02-25 16:41:00 Author: Speed Racer Posts: 156

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For the... less intelligent of us aaround here, could you go into the potential advantages and disadvantages of each? Not me of course but uh.... you know some people might just use a counter in every scenario and might not really understand why the two port superior would ever be the better option.The main difference is how it handles the case where both inputs are active at the same time. With a selector, it will chose the second option. This way you can fine tune whether both at once should be on or off, by choosing which port on the selector is the final result. With a counter, if both signals are activated simultaneously (Same simulation frame) it will end up set, but otherwise, it will take the stat of whichever signal was activated last.

2011-02-25 21:44:00 Author: Tygers Posts: 114

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