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While browsing through the datasheet of an ATMega324p description of a pin I noticed this symbol which looks like four diodes/triangles pointing at each other.

example symbol

So my question is what is it actually?

xZise
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1 Answers1

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It's a transmission gate or analogue switch:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/4243

The top connection should have an inversion bubble.

Leon Heller
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  • (+1) Worth mentioning is that the "inspiration" for this symbol comes from the valve symbol. The symbol shown in the question is the representation of two valves atop each other. An alternate symbol for a transmission gate is literally the valve symbol with control and negated control inputs. Wikipedia link that shows both symbols : https://en.wikipedia.org/wiki/Transmission_gate – Vicente Cunha May 18 '18 at 08:53
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    @VincenteCunha: Have another look at it. It's two triangular buffer symbols - one pointing left and one pointing right. – Transistor May 18 '18 at 08:57
  • @VicenteCunha I agree with transistor. I haven't got a reference at hand, but I don't think that symbol stemmed from the "valve" mechanical symbol. It's kinda two bidirectional buffers in parallel activated by two out-of-phase logic signals. Not the most simple and intuitive symbol, though. Meh! – LorenzoDonati4Ukraine-OnStrike May 18 '18 at 09:18
  • @Transistor Agreed, it definitely can be seen as two buffers. This interpretation also makes most sense if we consider only the electrical engineering context. But I would argue engineering areas borrow from each other, and in a "chicken and egg" argument, the concept of a valve came first to be (if we consider the history of technological development/needs). Hidraulic circuits and electrical circuits share some representation similarities, and the most notable one is that "triangles dictate flow direction", be it fluid or current. – Vicente Cunha May 18 '18 at 09:18
  • Example: a check valve behaves similarly to a diode, allowing flow in only one direction. One of the acceptable symbols used for check valves is literally the diode symbol used in electrical engineering. – Vicente Cunha May 18 '18 at 09:26
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    The bottom wire is the one with the inversion bubble in the OP. – ratchet freak May 18 '18 at 10:55