True, true.
Because of the fast rise/fall times of the 74AC\ACT outputs, you need to know what you are doing when building something with such chips.
Having a resistor in the output signal close to the chip certainly helps for long traces.

BTW: IMHO 74ALS seems to offer the best compromise of "speed versus trouble ratio" when driving long traces...

Hey, compared to differential ECL where half an inch of open wire at a signal line could make the difference between success and failure,
74AC\ACT isn't too bad.

Edit:
Slightly offtopic, but there seems to be CMOS TTL logic faster than 74AC\ACT: potato chips.
Power consumption isn't mentioned in all of the datasheets, and considering the related patent writings I think this topic was avoided intentionally.

74HC will work fine(*), but you can't reliably mix them with bipolars (74LS etc). After all, the 74HCT is just a 74HC with shifted input levels for compatibility.

People have overclocked the system with help of some 74F.

(*) Only the clock generator doesn't work well with a 74HC.

It's not entirely clear what you're saying here. I agree 74HC can't reliably be mixed with biplar families such as 74LS etc, but 74HCT can be mixed with those families -- that's what 74HCT is intended for.

-- Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

...as in "74HC output driving 74LS input will work, but 74LS output driving 74HC input can bring you into trouble".

For 5V powered 74HC, input logic level threshold is 2.5V.
74LS output at "logic high" with enough load probably could go below 3.0V.

One trick for getting around this is adding pullup resistors to 74LS outputs,
because a 74LS push/pull output can sink more current than it could source.

Yes, that's the reason we selected 74HCT for the kit edition. So you can always put in bipolars (as shown in the beginning of this thread). We also kept the '240 buffer to the ALU in the design for that reason, even if the fanout for CMOS parts is not the issue anymore.

Okay, all good, then. It just sounded a little odd when you said, "After all, the 74HCT is just a 74HC with shifted input levels" -- faintly implying, perhaps, that that's not appropriate.

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html