On 5/19/2010 7:07 AM, Invisible wrote:
> Ah yes. That's the fun thing about doing digital electronics. You can't
> just *buy* a 7400. No, you have to decide whether you want a 74LS00 or a
> 74HC00 or a 74HCT00 or...
>
> Reading the datasheets is like walking into another world. (Especially
> since the datasheets are usually poorly-scanned grainy PDFs that don't
> match the part number you actually asked about!)
>


A book that I found immensely helpful

http://www.amazon.com/CMOS-Cookbook-Second-DON-LANCASTER/dp/0750699434

Mine is well used and worn.

Great for getting off the ground quickly without spending hours 
searching the net.


Tom

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On 21-5-2010 15:53, clipka wrote:
> Am 21.05.2010 10:18, schrieb Invisible:

>> I have no idea how or why transistors work. But then, the entire _point_
>> of a logic gate is that it doesn't matter _how_ it works. It's a black
>> box. It implements a logical function. That should be all you need to 
>> know.

Wrong. See clipka's comment below. Also it is vitally important to know 
how a logical function is implemented if you are going to use it outside 
the logical specification. In particular the mathematical logical NAND 
is not specified if you leave one input open. What would a Haskell 
implementation do if you leave one input open?

> Note however that this black-box-knowledge should include the interface 
> characteristics - and knowing what goes on in a /simple/ logic gate 
> helps a lot to this end.
> 
> For instance, you should know how many inputs a logic gate output can 
> drive reliably; how an unconnected input behaves; how the gate creates, 
> and how it is affected by, noise on the power rails (and how to deal 
> with that phenomenon); how much current the gate draws, and what 
> parameters affect the power consumption (e.g. a TTL device will draw 
> current primarily due to its internal state, while a CMOS device will 
> draw current primarily due to changes of its internal state); and plenty 
> more such stuff.

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On 21-5-2010 16:15, Invisible wrote:
>>> Not that hard to figure out what kind of resistor you'd need to 
>>> safely drive an LED for a given voltage.
>>
>> I wouldn't have thought so.
> 
> Uh, how did this sentence end up saying the inverse of what I meant?

http://www.datasheetcatalog.org/datasheets/270/487906_DS.pdf

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On 21-5-2010 10:20, Invisible wrote:
> andrel wrote:
> 
>> Ok, Andy, here is the deal: we trust Ken in this, you put one of these 
>> books on your Amazon Wish list and you give me a link to that wish 
>> list. In exchange, after you received it, you read it and you stop 
>> asking questions that are answered in the book. Remember: Ken has also 
>> a copy.
> 
> My mother once said something to me, which I try to follow [although I 
> don't always succeed]. She said "if you don't have anything nice to say, 
> don't say anything".
> 
> If you think my questions are stupid or you don't feel like answering 
> them, then fine. Don't answer them. Ignore the thread or something. But 
> there's no need to make a point of telling me I'm stupid just because I 
> *dared* to ask for a few pointers. OK?

I think you missed the point entirely. You really need a book or 
something else that simply teaches you the basics. That in the end is 
much more effective than asking questions here one at a time. I don't 
have a book to recommend (I actually learned it from reading 
datasheets). Ken apparently has, so my suggestion is to buy that book. I 
can do that in two ways 1) simply say: 'Andy, buy that book', but that 
has the problem that I cannot decide how you should spend your money or 
2) what I said above. You are of course entirely free to see 2) as a 
less friendly way, just as I am allowed to be totally flabbergasted by that.

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scott wrote:

> You should never be leaving any inputs as floating anyway, that's just 
> asking for trouble (for example if you use a different IC series later). 
> Best to always tie your inputs to whatever you want them to be.

So what might be a good value for a pull-down resistor then?

(4.5V supply, 74HCxx ICs.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Am 23.05.2010 16:38, schrieb Orchid XP v8:

> So what might be a good value for a pull-down resistor then?
>
> (4.5V supply, 74HCxx ICs.)

A very common choice is 10 kOhm.

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>> So what might be a good value for a pull-down resistor then?
>>
>> (4.5V supply, 74HCxx ICs.)
> 
> A very common choice is 10 kOhm.

OK. That should only be a few pence...

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On 5/21/2010 9:57 AM, Invisible wrote:
>>> That and the subcircuit label...
>>
>> Actually, if you click on the subcircuit, you'll see some items in the
>> attributes window. One item is label. But, if you have multiple
>> instances of the same circuit and change the label for one, it changes
>> for all.
>>
>> Again, somewhat annoying.
>
> Yes, the "label" is so that if you have a dozen subcircuits, you can
> tell which type each one is. It's _not_ for labelling a specific
> instance. (E.g., if you insert a register, you can't label it with a
> register name. You can only label it with the kind of register it is.)
>

Right, but sometimes it would be nice to have a label that identifies 
the particular instance. At least, that's what I would expect when 
clicking on the item.

>>> It's trying to be helpful by detecting circuits which are unstable.
>>
>> I think it's more or less bailing out on a potential infinite loop.
>
> Hey, if it just wasn't handled, the program would crash. The fact that
> it's *noticing* the problem means that it's doing extra processing
> specifically to deal with it. But yes, it is a tad annoying. (Presumably
> the problem goes away if you use the built-in latch primitive...)
>

Well, of course the built-in latch primitive doesn't exhibit that 
problem. But with the Falstad app, the oscillation tends just to 
continue due to the way it's simulated. Logisim uses a propagation 
method where the values are carried from one component to the next, 
which can cause an infinite loop. Whereas Circuit Sim uses a timeslice 
method, where the entire circuit is calculated each tick, an oscillation 
can occur without any detriment to the program.

>>> Yeah. The whole wiring concept is just awkward. For example, Reactor
>>> (which has nothing to do with electronics but does involve wiring things
>>> together) has wires that go in a straight line from pin to pin. And when
>>> you move stuff, IT DOESN'T BREAK ALL THE WIRES OR RANDOMLY CONNECT THEM
>>> TO OTHER PINS! Sheesh, it's not rocket science...
>>
>> Actually, it can be a little tough to reroute wires when restricted to

>
> All I know is that I seem to spend more time trying to figure out how to
> move a component slightly to the side to make more space than actually,
> you know, designing my stuff! >_<
>

Yeah, Routing can be a pain when moving components. You can turn on an 
experimental feature where it allows you to sort of autoroute the wires 
in some cases when moving a component, but I've found if you move too 
far it will make bad connections. The algorithm that autoroutes needs to 
be a bit smarter, but I think it may be an instance of the halting problem.

>>> I'd prefer something less ugly to look at, personally.
>>
>> Well, sure, but function before form. I mean,
>>
>> this one was pretty, but was a pain to work with:
>> http://www.logiccircuit.org/
>
> What's up with it?
>

Not a clue... all the pretty ones aren't all that bright. ;)

>>> KLogic was easier to wire up. And it could do simulation graphs, which
>>> is extremely useful when you're trying to check, e.g., that your flip
>>> actually flops on the rising edge.
>>
>> Also, not available for Windows platform...
>
> I'd be surprised if nobody has ported it yet... but yeah, that's the
> least of the problems. A simulator that gives you THE WRONG ANSWER isn't
> very useful.
>

No, I suppose not. :)

>> http://www.falstad.com/circuit/
>
> I didn't even know that thing had logic gates...
>

It does. While it makes a great general circuit simulator, for anything 
non-trival its far from ideal for logic simulation, though.

>> The hex editor when I get finished with it will be very nice, though.
>
> No it won't. You'll never finish it. >:-)

Now I'll finish it just to prove you wrong, so ... Nyah!
-- 
~Mike

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>> Yes, the "label" is so that if you have a dozen subcircuits, you can
>> tell which type each one is. It's _not_ for labelling a specific
>> instance. (E.g., if you insert a register, you can't label it with a
>> register name. You can only label it with the kind of register it is.)
> 
> Right, but sometimes it would be nice to have a label that identifies 
> the particular instance. At least, that's what I would expect when 
> clicking on the item.

I won't disagree with that... ;-)

>> All I know is that I seem to spend more time trying to figure out how to
>> move a component slightly to the side to make more space than actually,
>> you know, designing my stuff! >_<
> 
> Yeah, Routing can be a pain when moving components. You can turn on an 
> experimental feature where it allows you to sort of autoroute the wires 
> in some cases when moving a component, but I've found if you move too 
> far it will make bad connections. The algorithm that autoroutes needs to 
> be a bit smarter, but I think it may be an instance of the halting problem.

The Halting Problem is unsolvable. I doubt wire routine is unsolvable. 
Finding the "perfect" wire routine sounds a bit like the Travelling 
Salesman problem, which is NP-Complete, not *not* unsolvable. And a 
routing algorithm which doesn't alter topology and gives "reasonable" 
results ought to be quite possible, though possibly not easy...

>>> this one was pretty, but was a pain to work with:
>>> http://www.logiccircuit.org/
>>
>> What's up with it?
> 
> Not a clue... all the pretty ones aren't all that bright. ;)

I tried it on Friday. Jesus, it sucks so hard! Eats RAM like candy, 
locks up for minutes at a time for no apparent reason, and doesn't even 
look particularly good anyway. Basically there's nothing to recommend 
it. (Plus I had to wait 30 minutes for the .Net framework to install...)

>>> http://www.falstad.com/circuit/
>>
>> I didn't even know that thing had logic gates...
> 
> It does. While it makes a great general circuit simulator, for anything 
> non-trival its far from ideal for logic simulation, though.

Yeah, it's designed to show you examples, not for serious design work.

>>> The hex editor when I get finished with it will be very nice, though.
>>
>> No it won't. You'll never finish it. >:-)
> 
> Now I'll finish it just to prove you wrong, so ... Nyah!

Heh. I'd like to see that. ;-)

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BTW:

http://sourceforge.net/projects/logicsim/

Requires .NET Framework 3.5

Only really just tiny pieces of the UI implemented, but you can sort of 
see how it will work.

-- 
~Mike

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