The Gigatron computer is all TTL, but in this case made up with some HCT, some LS, and some old-school proper 74 series. The differences are dramatic:

But wouldn't that be a function of "use"? As in, not all parts are being used the same. Therefore, some parts would get hotter than others the more they are used?

Or am I missing the overall point?

I do like that image though.

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Cat; the other white meat.

Maybe - unlike CMOS, TTL dissipates power even when it's standing still. It might be, though, that for example driving low takes more power than driving high, or vice versa. It's possible that the inputs dissipate different amounts of power depending on whether they are being pulled low or high...

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Shouldn't it be feasible to build a Gigatron using only CMOS chips?

Depends what chips they're using. Not all of the 74 series chips are available in all logic families, particularly some of the more complex ones like the 74x181 & 74x281 ALUs are, as far as I know, only available in TTL versions.

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The kit is supplied with 74HCTxxx chips, alas, you can't see this in this photo of my Gigatron:
Low res version


High res, but upside down version


The Gigatron web site is here

Mark

Regarding power consumption, each manufacturers version of a 74xxx series chip may be different (the function and pin-out are defined, not the actual internal circuitry, so this may be different between different manufacturers versions), each family will of course be different. And the current logic state of each chip may cause different power consumption, including the load that it's output pins are driving. The less power hungry chips will also have different power consumptions at higher frequencies compared to their static current consumption.

But in general terms, the original 74xxx are the most power hungry (compared to later versions).

Mark

Ah yes, the 74HCT series are CMOS chips with TTL-compatible input levels. But I was thinking of a pure CMOS version, without any TTL legacy involved.

For some more info about the innards of different TTL logic families, take a look at project 54/74.
It's about reverse engineering TTL chips (including CMOS).

Edit:
I think that CMOS is supposed to be as good as bipolar TTL nowaday when it comes to ESD discharge,
so because of the lower power consumption 74HC\HCT\AC\ACT CMOS is the better choise...
except if the chip you want to use isn't available in CMOS (74LS181).

Gigatron uses adders and multiplexers instead of 74181 for the ALU, avoiding this problem.

BTW: When it came to bus drivers, I had used 74LS\ALS\F\HCT\ACT245.
Signals on the bus had looked best with Fairchild 74ALS245.

With the danger of drifting off topic, but I am curious which type / range you are thinking of. The CMOS 4000 range maybe? The trouble here would be that the pin-outs are often different.
Or were you referring to the 74Cxxx or the 74HCxxx families? [I think there is a very good chance that the Gigatron would work if all the chips fitted were from the 74HCxxx family, 74HCTxxx were likely chosen so that it would work if mixed with 74xxx, 74LSxxx, 74ALSxxx and 74HCTxxx on the same board].
Or do you mean something completely different?

Mark

I do mean 74HC or 74AC series.

Once upon a time there were clearly separated 54/74 series TT-logic circuits on one hand and CMOS logic circuits on the other hand. Their pinnings were distinct in almost all cases. Then various variants of TTL were designed (H=faster/L=lesser power/S=with schottky diodes for acceleration/LS/and more). When they'd learned to dramatically increased the speed of CMOS circuits (HC) they copied known functions and pinnings between CMOS and xxx-TTL: you could buy a CD40174 which is pin compatible to a 74xxx174 as well as 74xxx4040 which has the same pinning as a CD4040. Today you can use these numbers just to say which pinning is inherited from which device/family. Nothing else.

A nice table is on wikipedia.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

You might have trouble with the 74AC series. There are some awfully long traces on the Megatron. They'd ring like church bells.

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Bill