The Hierarchy
Data types are categorized by their nature (Integral, Real, or Misc) and their simulation behavior (2-State vs. 4-State).
Integral
Real
Misc
2-State Types (Performance)
Simulate faster and take less memory (stores 0, 1). Ideal for testbenches and counters.
- bit: 1-bit unsigned (User defined size)
- byte: 8-bit signed
- shortint: 16-bit signed
- int: 32-bit signed
- longint: 64-bit signed
4-State Types (Modeling)
Accurately models hardware states (0, 1, X, Z). Used for RTL design and verifying resets.
- logic: User-defined size (unsigned). Replaces 'reg'.
- integer: 32-bit signed (Legacy).
- time: 64-bit unsigned (Timestamps).
Real & Misc Types
- real: Double precision float (Not synthesizable).
- shortreal: Single precision float.
- string: Dynamic array of characters.
- void: Represents non-existent data.
Summary of Built-in Types
| Type | Width | States | Signed? |
|---|---|---|---|
| bit | User Defined | 2-State | Unsigned |
| logic / reg | User Defined | 4-State | Unsigned |
| int | 32-bit | 2-State | Signed |
| byte | 8-bit | 2-State | Signed |
| integer | 32-bit | 4-State | Signed |