SystemVerilog Data Types

Part 1 of 9Language FoundationsIntermediate

5topics
5lessons

Every declaration answers two questions: can this bit hold X or Z, and is its value resolved from drivers or stored. The five lessons below turn those answers into habits for ports, casts, and testbench types.

Two questions pick the type: must the value show X and Z, and how many things drive it.

Lesson	Path	What it covers
4-State vs 2-State Types	Required	X and Z modelling, the 2-state discount, the guarded boundary, and X tracing.
Nets vs Variables	Required	Resolution against storage, one-driver logic, and buses that still need wires.
Integer Types & Casting	Required	Widths, signedness, the three casts, and silent truncation rules.
Enums, Structs & Unions	Recommended	Named states, shaped vectors, shared storage, and checked conversions.
Strings, Reals & Special Types	Optional	Dynamic text, testbench reals, opaque handles, and event sync. Optional because `real` and `chandle` only matter for models and DPI: read it when you hit one.

Path: Required is the core first pass for this part's goal, a self-checking testbench; Recommended is what most learners should read; Optional is reference, specialist or revision material to return to later.

Check yourself Testbench code copies a DUT bus into a 2-state variable and the checking code sees clean zeros. Where did the X go?

The 4-state to 2-state copy mapped X to 0 silently. The first lesson guards that boundary with an explicit unknown check before the copy.

Up next4-State vs 2-State Types

Practice this lesson Previous lesson Report an error

Lesson

Path

What it covers

4-State vs 2-State Types

Required

X and Z modelling, the 2-state discount, the guarded boundary, and X tracing.

Nets vs Variables

Required

Resolution against storage, one-driver logic, and buses that still need wires.

Integer Types & Casting

Required

Widths, signedness, the three casts, and silent truncation rules.

Enums, Structs & Unions

Recommended

Named states, shaped vectors, shared storage, and checked conversions.

Strings, Reals & Special Types

Optional

Dynamic text, testbench reals, opaque handles, and event sync. Optional because real and chandle only matter for models and DPI: read it when you hit one.