This was prompted by a question on the electronics site (which was asking why only an open collector variant of a particularly old part existed and how it could be part of a data bus).

This was a pretty important development as it revolutionised bus interfacing (such as memory systems) among other things.

I know that 3 state (tri-state in National Semiconductor parlance which was [is?] trademarked) came out sometime in the (early) 1970s but I am trying to pin it down to at least a year range.

I have tried searching for the date of the trademark without success so I am asking this here in the hope people here might remember their first parts with this feature.

I have found a citation at ACM from 1978 that references this, but I am not sure if actual parts were in the wild prior to this. My first parts using this were in the early 80s (so I know it existed by then).

Note that I am looking for the first commercial implementations.

I would appreciate any insight.


I don't know how to prove a first commercial implementation, but the Texas Instruments System 74 Designer's Manual (copyright 1973) includes the 74125 and 74126 quad 3-state buffers.

A Motorola TTL databook from 1971 doesn't include these circuits. Neither does a Signetics databook from 1972.

(I found all these references linked from this project5474.org page.)

  • Interesting; I used to have the dead tree editions of those at one time (lost many a move ago, though). – Peter Smith Dec 12 '19 at 16:28
  • I'd hoped I might have something contemporaneous on the dustiest shelf at home, but the oldest thing I've got is a 1976 TTL databook. In the late 70s and early 80s when I was a happy digital hobbyist, I wanted the newest books I could scavenge, not the oldest. Sigh... – jeffB Dec 13 '19 at 3:29
  • This pins the dates down to a reasonably close estimate (around 1972 give or take a year) and is really very useful when educating others (as many of us try to do) as to just why open collector bus implementations existed (and indeed still exist today). – Peter Smith Dec 14 '19 at 14:38

National Semiconductor had the name Tri-State and introduced the first commercial devices. Texas Instruments and others adopted three-state logic into their product lines afterwards. There will be multiple search hits on Dale Mrazek who invented the logic family and National Semiconductor. NatSemi was always recognised due to the hold on Tri-State name.


  • 2
    Thanks for taking the time to answer, but this doesn't actually say when three-state was commercially introduced, which is the question here. – cjs Dec 13 '19 at 0:09
  • This is very useful background information and it helps me to dig a bit deeper as well. Thanks! – Peter Smith Dec 13 '19 at 9:39

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