ghall426

I'm trying to figure out the differences between the 4000 series and 7400 series IC's. I know the 4000 are CMOS, have been around longer, use less power, but are slower. The 7400 series are TTL, newer, faster, but use more power.

But then the 7400 has low power 74LS00 versions and CMOS compatible 74HC00 versions. It all seems very confusing to pick the right type. I want to build up an on-hand inventory of various chips but am not sure what to buy.

So what are people actually using in new circuits today? Does it still just depend on the speed required of the circuit and if it's battery powered or not? What do you guys typically use and why?

Greg

Nigel Goodwin

You 'know' wrong then, TTL has been about FAR longer than CMOS - and TTL uses a GREAT deal more power than CMOS, thousands of times as much (if not millions).

The HC series are just CMOS chips, not really 74 series at all - the LS series while 'low power' are only a bit lower than normal TTL, still thousands of times worse than CMOS.

You're in the wrong century, TTL and CMOS are very old technology, probably 99+% of their use has now been replaced by micro-controllers.

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audioguru

Old 74xx and newer 74LSxx TTL ICs need a supply of 5.0V.
Newer 4xxx Cmos ICs use a supply from 3.0V to 18.0V.
There is also 74Cxx which is the same Cmos as 4xxx but with pin numbers and part numbers as 74xx.
Newer 74HCxx high-speed Cmos ICs work with a supply from 2.0V to 6.0V.

74HCxx has the same pins numbers and part numbers as old 74xx TTL ICs.

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eblc1388

And there is the 74HCT series which is a near replacement for the 74LS series.

Both works on 5V only but HCT use 1/1000 of the power that 74LS does.

However, it is a bit slower than 74LS (25MHz vs 35MHz). The HCT output can source and sink 20mA while that of 74LS can only sink 16mA but source 2mA.

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L.Chung

ghall426

I've been given a lot of technical information now. Thank you. But one question hasn't been answered much. What chips are most popular for building circuits today? Is it really PICs and microcontrollers now?

For example, I just built a scoreboard circuit and used the 4000 series chips because I needed 6 volts to power the displays. What would be the deciding factor to use the 4000 series or 74HC00 series or something else? (besides a PIC)

Greg

Hero999

It depends on what you're doing and what equipment you have.

If you just want to flash an LED, debounce a switch or build a simple counter or timer then logic chips are still used however for more complex functions PICs are the only realistic solution.

I don't have a programmer so I don't use PICs but I really haven't had the need for one.

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ghall426

So what series of chips do you typically use and why?

Nigel Goodwin

CMOS 4000 series are far more popular than TTL, wider voltage range, vastly less current - just better overall.

Yes it is, why use 20 or 30 TTL/CMOS chips when you can get better performance from one single cheap little chip!. Even silly things like a 555 timer!, you can use an 8 pin PIC that's the same size as a 555 - but get far higher performance from it as a timer.

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Hero999

However whilest that is true CMOS has its disadvantages:

• More susceptible to damage caused by ESD than TTL.
• Taking a pin above or below the supply can result in distructice latchup.
• Uses more power than LS TTL at higher frequencies.

Also true but a 555 timer gives you the following advantages:

• Cheaper - 555 + resistor + capacitor costs less than PIC + crystal especially if you don't have a programmer.
• Easier to use - no programming, just add a resistor and capacitor and you're done.
• High output capacity, push-pull up to 200mA, (100mA for CMOS types).

Don't get me wrong, I'm not anti-PIC, I'm considering buying a programmer they look quite fun.

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Styx

horses for courses 74HCxxx for me, the noise-imunity is a benefit
plus 74 is widly used in the Aerospace ind

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Nigel Goodwin

The 74HCxxx are just CMOS versions of the 74 series, perhaps the best of both worlds?.

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Nigel Goodwin

A CMOS 555 isn't much cheaper than a PIC - checking Maplin (who aren't particularly cheap) a 7555 is £1.28 and a 12F629 is £1.45 - a normal 555 is only £0.53 though (but consumes a LOT!! more current).

The 12F629 has an internal oscillator, so can be used without a crystal - although it's nowhere near as accurate - but it will still out perform a 555 timer by many, many times.

The other advantage is that you can often reduce the rest of the circuitry as well - depending what you were using a 555 for in the first place - not to mention you can enhance designs easily.

Quick example - a 555 egg timer:

555 version isn't likely to be terribly accurate - PIC will far out perform it.

Add functionality - how about flashing the output LED, gradually getting faster and faster until it's always on at the end?. Not easy to do with a 555, but trivial with a PIC, and using less components than the original 555 design.

Quick edit:

Exactly same hardware as above - no change at all - reprogram PIC, now becomes a timer that lights an LED for 1 hour once a week - try that with a 555?

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Hero999

I agree with you, but if all you want to do is flash a pair of LEDs alternately at about 1Hz then the PIC offers little advantage.

How stable is the internal oscillator?
I would believe you that it's probably more acurate than a simple RC oscillator but how does it compare with a crystal?

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hjames

Read this:
http://www-s.ti.com/sc/psheets/sdyu001y/sdyu001y.pdf
Specifically page 1-6 and up.

As soon as you start talking about modern portable devices, you'll start seeing logic devices that work at 1.8V - parts in the "LVC" families and such - much faster than the HC devices, and all other nice properties - look at the chart.

Simple gates are used as glue logic between bigger silicon parts - microcontrolleres/asics/fpgas. They're also pretty useful as IO devices - shift register, latches - when you need to get a little extra functionality, and don't want to go to the next size microcontroller/etc.

Nigel Goodwin

It's nowhere near a crystal, it's only an on-chip RC oscillator - there are graphs in the datasheets showing expected performances. But it's a lot better than an external RC, and hugely better than a long time period 555 - because of the programming ability you can get long times from a fast oscillator - just like using a fast 555 feeding a series of CMOS counters, except it's more accurate than the 555, and it's all in one small package.

Actually, for 1Hz flashing LED's, it would still be simpler (less external components) than a 555 - and if you used a 6 pin 10F SM series PIC, it would be smaller as well. But generally, unless you're improving or enhancing, it wouldn't be worth while.

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