Digital Logic Toolkit

Digital Logic Toolkit — Buffer

Source
https://digitallogictoolkit.com/buffer-gate/
Printed

Three-state buffer, enable = 0 — buffer gate

corethe value that is not a value

Answer

Y = 0

Why this example is worth doing

Disabled, the output is disconnected — high impedance, written Z — which is neither 0 nor 1 and does not belong in a truth table as a logic level. The page is emphatic on this because it is the first place a student meets a third state and the natural assumption is that Z means 0. Z means the wire is floating, and what voltage it settles at depends on whatever else is attached.

Try your own input in the Buffer. Truth table, symbol and algebraic form for the non-inverting buffer, and what it is for.

How the answer is reached

The probed row

A = 1, OE = 0

Output table

Output table — columns A, OE, Y
AOEY
000
010
100
111

Compare with

Open the Buffer

This input is entered in the tool itself — it is too rich for a link to carry.

Note:

Notation this page assumes

  • Symbols: · is AND, + is OR, ⊕ is XOR, a prime or an overline is NOT. The field also takes ∧ ∨ ¬ ~ ! & | and the words.
  • Operator precedence, tightest first: NOT, then AND (including juxtaposition), then XOR/XNOR, then NAND/NOR, then OR, then IMPLIES, then IFF.
  • Gate symbols follow whichever standard the header toggle is set to: ANSI/IEEE Std 91-1984 distinctive shapes, or IEC 60617-12 rectangles.

Sources

  • ANSI/IEEE Std 91-1984, Graphic Symbols for Logic Functions
  • IEC 60617-12, Graphical Symbols for Diagrams — Binary Logic Elements