Attributes

Language defined attributes return information about certain items in VHDL
- Types, subtypes
- Procedures, functions
- Signals, variables, constants
- Entities, architectures, configurations, packages
- Components
Attributes can be user-defined to handle custom situations (user-defined records, etc.)
VHDL has several predefined attributes that are useful to the designer

General form of attribute use

name ' attribute_identifier ' read as "tick"

Some example predefined attributes
- X'EVENT -- evaluates TRUE when an event on signal X occurs
- X'LAST_VALUE -- returns the last value of signal X
- Y'HIGH -- returns the highest value in the range of Y
- X'STABLE(t) -- evaluates TRUE when no event has occured on signal X in the past t" time