I've designed a circuit to choose between two 8-bit digital buses. I'm taking advantage of the fact that the 74AC540/541 chips have tristate outputs, so can enter into high impedance state to allow the other chip to drive the bus without creating a short.
I'm using the
!BYPASS digital lines to enable and disable each bus. These lines are controlled by a DPST mechanical switch and pull-up resistors:
I'm worried about the switching operation: as the switch is toggled, I cannot guarantee that the two buffers will not be on at the same time and therefore, depending on their inputs, short their outputs together. For example, pin 2 of N2A could be LOW, causing its (inverted) output to be HIGH, whilst pin 2 on N8A might be LOW, causing its (non-inverted) output to be LOW, and creating a short between those two outputs. I imagine that switching operations with these chips are not instantaneous, and might not be matched, so there could be a situation where both chips are momentarily on during the switching operation (even with a break-before-make switch - I think).
How can I avoid shorts during this switching operation?