[sdiy] CMOS chip questions

[Dan Snazelle]

what about if you need higher supply? (+12volts) is there any replacement for 74C??

thanks




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> From: usenet at teply.info
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] CMOS chip questions
> Date: Sat, 18 Jul 2009 14:49:17 +0200
>
> Am Saturday 18 July 2009 01:48:01 schrieb Scott Nordlund:
>> 74HC is usually fine. I prefer 74HCT since its inputs are TTL compatible.
>> If you need something faster, use 74AC. The problem with diode logic (I
>> guess you're using diode resistor logic?) is that you can't really chain
>> stuff together. The speed depends on your choice of diodes and resistors
>> as well as whatever you're driving. I believe TTL circuits prefer pull-up
>> resistors rather than pull-down (doesn't matter with CMOS), so this may
>> limit your options in some cases.
>>
> I'll agree totally here, 74HC instead of CD4xxx is usually just fine unless
> you really need the devices to withstand 15V Logic levels. And in the 74HC4xxx
> series you'll get the very same pinout as the original CD4xxx devices, so
> that is a non-issue as well. With most small-scale suppliers, 74HC has better
> availability than CD4xxx anyways. When it comes to single gates, there are
> such on the market as well. Okay, all i've seen are SMT devices, but when you
> need to save real estate, i'd go for that anyways. It ain't no black magic. A
> bit pricey in terms of $$/gate compared to the usual 4-gates-in-a-case stuff,
> but a lot easier to work with considering all those design questions popping
> up when working with discrete Diode-resistor logic. And: if you should happen
> to not use some gate in a case, you'll most likely be better of with spending
> a couple resistors and tieing those inputs to high or low.
> Regarding 74HC vs. 74AHC vs. 74AC in most cases you're safe going for 74HC.
> Coz, when you actually need the additional speed of 74AC and AHC compared to
> plain 74HC, you'll know anyways. In all those cases with SDIY i've ever come
> across, 74HC had plenty of speed and still loads of margin. It's not like
> clock jitters of half a nanosecond would kill us here.
>
> HTH,
> Florian
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