74 logic families

[jlangvand]

Hi

I've decided to build my own custom CPU, much inspired by Magic-1, D16/M and others. I want to use 74 logic gates for most of the functionality. But i've not settled for any specific family yet.

At first I thought about using the LS family, but I would like to be able to cranc up the clock a bit later on. The Magic-1 uses mostly LS, and runs stable at 4.09MHz. The D16/M uses mostly HC logic, and can run at 8MHz, though effectively 4MHz.

There's alot of different families like the AC, ACT, ABT etc. with low propagation delays, but I don't know anything about the cons, if any, by using these.

Of course, finding an ALU like that might be impossible, but that could be built up using muxes and other basix functions.

Any help would be appreciated!

 

[alec_t]

If I were doing this I'd first see what ALUs are available at a sensible price, then work from there.

 

[jlangvand]

That's a problem, indeed. I see I weren't very clear in my first post.

The old 74 series ALUs in DIP packaging are hard to find, and there are few different types to choose from, I think. So I think I'll have to build one myself using basic logic functions. It will probably require an extra board for all the logic, but the result may be even better than using a 74181/74381. I've found some info on this already.

So the ALU does not need to be the bottleneck in the design.

So what I'm actually asking is which family is best suited for high clock speeds, and important considerations regarding types like AC and ABT..

I hope I'm more clear here

 

[Mikebits]

I would go with ACT or maybe LVT, LS is a power hog.

 

[jlangvand]

ACT seems like the best choice so far.. I would like to stick to 5V logic. Thanks.

 

[unclejed613]

I would go with ACT or maybe LVT, LS is a power hog.

i remember when "LS" meant "Low power Schottky"

 

[jlangvand]

i remember when "LS" meant "Low power Schottky"

I asked Bill Buzbee, the man behind the Magic-1, about his choice of LS. This is what he said: "I mostly used 74LS because of availability. That family was commonly used in the 70's and 80's because of its good tradeoff between speed and power consumption. I already had a lot of it on hand. For the critical logic paths, I used 74F."

I think I'll go for the ACT. Seems like it's relatively inexpensive and good availability.

 

[jlangvand]

Double post, sorry.

 

[Mikebits]

Have a look at this glue logic selection guide.

http://www.interfacebus.com/Design_Logic_Family_Selection.html