Now, I know that this question has been asked so many times that it seems like I'm trolling, but I must point out that I couldn't find the right answer to this question anywhere.
So yeah, CMOS and TTL are different. Logic levels, speed, drive current, power consumption, and so on.
What I'm wondering is what is their difference from a designer's perspective.
For this question, I'll be designing a small computer, say, a Z80 or a 6502 or 8080 or whatever. Let's use HCMOS and LSTTL as our examples.
Does it really make a difference, practically?
The clock rates are low enough that gate delays are not an issue. I'll power this from AC mains so power is not an issue. I'll stick to one logic family or the other so compatibility is not an issue. So what's the incentive to choose one over the other?
Say I want to make this device as reliable as possible. Also, I want to make this device repairable.
So which logic family should I use?
I'm talking about product lifetime. Should I stick to one type of IC because they are more reliable? What's the MBTF of these devices?
Also what if, in a few years, they stop manufacturing some of these ICs? For example, if you've got a Motorola ECL-family computer, if an IC breaks, you're outta luck. You'll have to kludge your own or scrounge for some old rare ICs. I've heard that large FIFOs and PROMs and SRAMs in the 74xx family have also been discontinued. So if something breaks, I want to be able to buy readily-available parts and fix it.