04.4 Tri-state drivers

When two gates want to change an input of a gate.

We cannot link them directly → short circuit

⇒ Let’s instead use MUXes or tri-state drivers

They have 3 states :

• z : undefined
• $0$ : off
• $1$ : on

They are built from a data input $w$, an enable input $e$ and an output $f$

$e$	$w$	$f$
$0$	$0$	z
$0$	$1$	z
$1$	$0$	$0$
$1$	$1$	$1$
We have a few different types of tri-state drivers

Active high and active low → low inverts the $e$ signal

04.5 Bus