What is this quadruple triangle logic symbol?

Question

Or maybe it is two mirrored triangles... and an 'invertor' dot?
enter image description here

This is from a diagram in the ATMega328P datasheet, page 76 bottom left.

Note that this question shows a similar device. In that question however the symbols only have two ports and no dot/circle.

This symbol stands for transmission gate. Some details here. I haven't read the ATMega datasheet, so I can't comment on the purpose of the transmission gate in that diagram. — Nick Alexeev, Jul 14 '14 at 06:05
That specific transmission gate disconnects the read logic from the external pin when the chip is sleeping. — Ignacio Vazquez-Abrams, Jul 14 '14 at 06:31

Wouter van Ooijen · Accepted Answer · 2014-07-14T13:31:37.063

As Nick states, it is a transmission gate. Think of a TG as a switch that can connect or disconnect the horizontal line.

As Ignacio states, in this particular case the TG is used to disconnect the external pin from the digital input synchronizer when the chip is in SLEEP mode. Note that at the same time that input is grounded by activating the FET.

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Note that the signal that is passed to the synchronizer is digital , so in normal operation a TG would not be needed. The only reason I can think of to use a TG (instead of a simple gate) is that in sleep mode the value on Pxn might not be a valid digital signal, which would cause excessive switching and hence current consumption of the schmitt-trigger and subsequent circuitry.

The standard implementation of a transmission gate is two FETs in parallel, one P and one N. The two FETs require opposite switching signals.

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Any idea why the SLEEP signal is connected to both sides of the TG? Am I right the bottom 'port' is inverted? — RJR, Jul 14 '14 at 08:48

What is this quadruple triangle logic symbol?

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