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ALU 54LS181

A project log for One-instruction TTL Computer

A breadboard-able computer which uses only a single instruction - MOVE

Justin DavisJustin Davis 04/20/2017 at 11:474 Comments

So I'm already running into difficulties with parts. Fortunately I can dig well and came up with this guy:

http://www.ti.com/product/SN54LS181/description

It's an active 181 ALU. Sure it's the 54181, but it will work just fine. I'm not against the 5400 series. And it makes my life much easier. And it's an active device, so it qualifies. Sure it's just 4-bit, but it's easy to gang them together.

Discussions

Justin Davis wrote 04/20/2017 at 19:22 point

I'm not able to find a '381 that's active (or '382).  Plus it's not cascade-able because it doesn't have a carry-out bit.  I think I can make do with two '181s.

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Yann Guidon / YGDES wrote 04/20/2017 at 20:31 point

it's cascadable, IIRC, because it exposes the Propagate and Generate signals.

OK, I don't know either how to use these :-D

Yes, the '181 is bulky but usually a good bet (and nice heater for the long winter nights)

Do you really need "active" parts ? I did find some 381 on the 'bay.

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Justin Davis wrote 04/21/2017 at 00:38 point

Even though this is a personal project, I find it difficult to break away from good design practices.  One of the highest is don't use obsolete components. If anyone else wants to build the project, I'll want them to gets parts easily.  And obsolete components are often more expensive and of questionable quality and functionality.  I don't really trust a chip that's been sitting on a shelf for 10-15 years.

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Yann Guidon / YGDES wrote 04/20/2017 at 18:51 point

The '181 seems to be trendy these days :-)

I got a few vintage ones https://hackaday.io/project/8121-discrete-yasep/log/28438-what-chips-for-the-alu and I've seen it appear on several projects here, as well as on the main hackaday.com site 

https://hackaday.com/2017/03/27/explaining-the-operation-of-the-74181-alu/

https://hackaday.com/2017/01/07/yes-you-can-reverse-engineer-this-74181/

The 381 might be more convenient and smaller as well.

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