Computer-aided Design (17)
Symbolic Logic Signal Values
- Designers sometimes need signal values other than just 0 or 1.
- Logic signal values are represented by a state and a strength.
- A third state X represents an unknown state or a potential problem.
- Truth tables for three-valued logic (with X added)
-
-
-
-
- Signal strength values:
- Forcing (F): signal line is strongly forced to a given state.
- Resistive (R): signal line is weakly forced to a given state.
- Floating (Z): signal line is not forced forced at all.
- Unknown (U): signal strength cannot be determined.