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Forum section: electronics / projects

author: daywalkerdha
author_rank: Contributor
timestamp: May 10, 2013, 08:01:16 pm
content: no text

author: mikes
author_rank: Regular Contributor
timestamp: May 10, 2013, 08:17:07 pm
content: Rather than making us figure out what it does, why don't you describe what you want it to do? Is speed critical?You could use an 8 pin PIC microprocessor (12F508?) to mimic any (?) 2 in 2 out logic circuit. Just not sure if it would be fast enough.

author: TerminalJack505
author_rank: Super Contributor
timestamp: May 10, 2013, 08:22:56 pm
content: For discrete logic, using multiplexers is usually the best way to implement truth tables.The booksThe Art of ElectronicsandPractical Electronics for Inventorsshow how. I'm sure there are plenty of examples on the web too.Attached are a couple of examples.

author: ddavidebor
author_rank: Super Contributor
timestamp: May 10, 2013, 08:39:55 pm
content: you can use a 3 bit multiplexer.you only need to do your equation in the form where you have all the variable in all the term likeabc+abc+abc+abc+abc+abc+abc+abc (obviusly some are negated)next you have your multiplexer that has 8 input that correspond to binaryabc000001010011100101110111so when you see zero it's the variable negated , when you see 1 is normaljust short to vcc the term you need and to gnd the other

author: ddavidebor
author_rank: Super Contributor
timestamp: May 10, 2013, 09:16:22 pm
content: Go for the mux, you'll need only one chip and super simple pcb design

author: nctnico
author_rank: Super Contributor
timestamp: May 10, 2013, 10:24:59 pm
content: Or use a GAL16V8. Back in the old days I used these for all kinds of odd logic handling. Just write a few simple logic equations and done (let the software deal with optimisation). Even stuff like single push-button on/off is possible. If the customers wants it different then its just a matter of reprogramming.

author: MasterOfNone
author_rank: Regular Contributor
timestamp: May 10, 2013, 10:45:33 pm
content: There you go then, I can’t seem to get it simpler that this

author: electronupdate
author_rank: Regular Contributor
timestamp: May 10, 2013, 11:07:19 pm
content: Do you have a timing diagram or state diagram, or even a word description of what this circuit does?When I simulate it, it appears that in some states the flip-flops set and then reset themselves.... assuming a gate delay this creates a very poor quality oscillator. Is that your intent?For outputs you should consider a different label, perhaps "OUT1" and "OUT2". A* and B* traditionally would refer to inverted versions of your A and B signals respectively.Quote from: daywalkerdha on May 10, 2013, 08:01:16 pm

author: amyk
author_rank: Super Contributor
timestamp: May 11, 2013, 12:00:46 pm
content: My best guess is that it's a phase detector of some sort...If your simulator's gate delays are all the same then a flip-flop can be made to oscillate. In the real world that's a race condition and it'll probably settle at one state or another randomly.

author: FJV
author_rank: Regular Contributor
timestamp: May 11, 2013, 02:57:58 pm
content: You can do this by using a Karnaugh map / diagram.A quick search would get you started.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 11, 2013, 05:54:10 pm
content: Quote from: nctnico on May 10, 2013, 10:24:59 pmThis. The GALs have long been forgotten in favor of their FPGA big brothers. The little GALs need some love tooIs anyone still making them? can you still buy them?? sometimes you don't need a full CPLD , the GALs and PALs can still be useful, but I think no one makes them now.

author: nctnico
author_rank: Super Contributor
timestamp: May 11, 2013, 06:26:18 pm
content: There are still lots of small CPLDs similar to the old GALs out there from Lattice, Xilinx, etc.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 12, 2013, 12:53:31 am
content: Quote from: nctnico on May 11, 2013, 06:26:18 pmYes, I'm familiar with the MACHXO2 from Lattice, used it in a design once. But it's still more dense than a GAL. I have not used the new ICE series from them. Costs are always coming down... if I found a point in a design where I needed just a small logic device, but all I could find was a small CPLD from Lattice, for example, then I would rethink the design to remove even more components and put more into the CPLD