An FPGA built with 7400 series logic [video]

Back in the late 70s and 80s, many computers and other digital systems were actually designed using basic blocks similar to this. Since chip layout is by far the biggest expense (especially back then) it made sense to design just one customizable chip, and then produce it with different metal layers to configure it into various arrangements, so it is relatively easily "programmed" just before manufacturing. DEC's ill-fated VAX 9000 was done in this way, probably the last great pre-CMOS processor design, with hundreds of ECL gate array chips all based on a couple die patterns. Unfortunately the benefits of sheer density from CMOS were undeniable. When they crammed the VAX into a $1000 CMOS microprocessor, it outperformed the $1 million VAX 9000 four years later. These days it's relatively uncommon as a technique except for rapid prototyping. With standard cell ASIC designs, a gate array cell able to perform any function is still an option, but modern design tools make it much easier to use more optimized logic.

Full writeup (first in series, each post links to the next): <a href="https:&#x2F;&#x2F;mnemocron.github.io&#x2F;2023-12-08-DIY-FPGA-diary-0&#x2F;" rel="nofollow">https:&#x2F;&#x2F;mnemocron.github.io&#x2F;2023-12-08-DIY-FPGA-diary-0&#x2F;</a>

<a href="https:&#x2F;&#x2F;github.com&#x2F;mnemocron&#x2F;my-discrete-fpga">https:&#x2F;&#x2F;github.com&#x2F;mnemocron&#x2F;my-discrete-fpga</a>

Completely tangential, but I recently realized how annoying 7400 series is.<p>First annoyance is that manufacturers generally put the logic tech family in the middle, so you got 74HCxxx or 74LVCxxx. This makes searching information very annoying because you can&#x27;t just do a simple prefix&#x2F;suffix match. And of course those logic family names have no rhyme or reason, nor are they consistent across vendors.<p>Some parts are also available as 5400 series logic, which makes things even more confusing.<p>Some manufacturers like to throw some letters like SN in front of the 74... part number, making even more difficult to search, or visually scan them. Others don&#x27;t put any letters in the front<p>At some point some people thought to integrate all of 4000 series logic into 7400 series, so you got some parts that are seemingly logically equivalent but have different part numbers because they come originally from 4000 series instead of 7400 series.<p>The logic family names can also contain digits, so figuring out where the family name ends is not that easy.<p>Like almost all parts, manufacturers love throwing some extra characters in the end to indicate stuff like packaging.<p>The part specs can vary quite a lot between manufacturers, even on nominally same logic family like the popular &quot;74HC&quot; series<p>basically we have gone from 7404 to something like SN74AUP1T04DCKR<p>all this adds up to finding parts being very annoying when building stuff