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Comment by dbcurtis | Hacker News Reader

I'm lucky enough to say this was my day job in the 1980's. The sad thing is that today the TTL catalog is much thinner, so it is actually harder to do today than it was then. I'm happy to see RISC-V getting so much traction with serious builders. It seems like the most viable path to hardware freedom right now.

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The 74 logic family is gone, because it's been fully obsoleted by newer logic families (especially 74LS and 74HC). The vast majority of parts from the 74 family are available in these families, which generally have compatible behavior, equivalent or higher speed, and much lower power draw.

There are some old parts from the 74 family which were never brought over (like the 7447 seven-segment decoder), but all of the basic logic parts are still around.

Most specialty (in the higher up numbers there are quite a lot of these) parts only existed in a single family anyway. But basic stuff, muxes, dividers, registers/drivers etc. all made it to HCMOS :)

This is one of my old favorites. I never used it, but it had some of the most speciality logic out there:

4-Bit Arithmetic Logic Unit http://ee-classes.usc.edu/ee459/library/datasheets/DM74LS181...

The 74181 was a really cool classic part, and was used in a lot of discrete CPUs.

Unfortunately, it's one of the parts that never made it past the 74LS family. :(

But... on a purely philosophical note, are you really building a CPU from gates if you use a '181?

With that said, the capstone project for my college electronics course was to build a 4-bit computer from 74LS chips, and we used the '181. The instructor explained that it was a necessary simplification, in order to get the project into the space and time available. We were provided with the schematic, but were expected to get it working with little or no help, and to demonstrate operation of a program. I wrote a dice game.

Not true...Philips did at least a 74F and 74HCT version, and TI did a 74AS181. Weirdly, Hitachi did a 74AC182 (lookahead carry generator for '181), but AFAIK only the 74HC181. Never figured that one out. There's also an ECL version (MC10181).

If you jumped to the 74381 you could get nifty things like the IDT7381 or L4C381, which are the equivalent of 4 '381s in a PLCC package that ran at a 25ns cycle (faster, I think, as well).

RISC-V isn't about hardware freedom, but about an open ISA that anyone can implement, including those who will make proprietary implementations.

The fact that RISC-V is not motivated by hardware freedom is not in conflict with my statement that it is a beacon of light on the road to hardware freedom. Both can be simultaneously true.

Hardware freedom will become increasingly important in the future, and I predict it will be harder to achieve that software freedom.

That sounds like it would have been very interesting! Back in the 70's it wasn't an uncommon "hobby project" to build a very simple "CPU" using TTL parts. While the computational utility was obviously limited it was a great learning exercise.

I remember working out the logic of "JK" flip-flops and the like. At one time I'd acquired some ancient vacuum tube versions of said flip-flops. Wish I'd kept them, they'd be a great curiosity today, a collector's item of sorts.

Should evoke some good memories looking through the catalogs of current versions of those venerable products. Won't be surprising if they'll be around for a long time into the future.

What do you mean by the TTL catalog is much thinner?

TTL = transistor transistor logic

This is the technology in the common 74' series integrated circuits that became popular in the late 1960's and 1970's. You can get basic IC's that perform AND, NOT, XOR operations but also more complex IC's that perform as multiplexors, buffers, registers and so forth. You can find these in computers like the PDP or VAX series machines.

They are not used as much today and so less of them are still manufactured.

Although when we say TTL/74 today, usually HCMOS is meant. Real TTL 7400 series parts are, I think, all EOL and have been for many years.

Looks like 'F' is still available:

http://www.nxp.com/documents/data_sheet/74F74.pdf

TI still makes a lot of them, but you have to mix and match series if you want broad coverage of the device family. This document is a very helpful overview of their range and how they interoperate: http://www.ti.com/lit/sg/sdyu001aa/sdyu001aa.pdf

(fwiw it sounds like you know what you're talking about; I just wanted to share this info for anyone else who might be interested)

Ah ok, you were referring to the catalog of actually being able to order these types of first generation ICs I see. Yeah I would imagine it would be nice market - basically the hobbyist if that. Cheers.

Fewer chips.

Many, many of my favorite 74' parts from the old days are no longer made. The MSI parts that were bread-and-butter of this kind of design back then make less-than-zero economic sense any more. Nobody would design them in, so nobody makes them.

Today you can get the basic logic, of course, because a little bit of glue and duct tape is still necessary. And the super basic shift registers and I/O buffers are still useful. But all computation has moved into much more highly integrated chips or FPGAs.

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