Advanced Usage of Verilog Date Types

a) Physical data type
• Net (wire, wand, wor, tri, triand, trior). Default value is z. Used mainly in structural modeling.
• Register (reg). Default value is x. Used in dataflow/RTL and behavioral modelings.
• Charge storage node (trireg). Default value is x. Used in gate-level and switchlevel modelings.

b) Abstract data type — used only in behavioral modeling and test fixture.
• Integer (integer) stores 32-bit signed quantity.
• Time (time) stores 64-bit unsigned quantity from system task $time.
• Real (real) stores floating-point quantity.
• Parameter (parameter) substitutes constant.
• Event (event) is only name reference — does not hold value.

Examples:
4'b1011 // 4-bit binary of value 1011
234 // 3-digit decimal of value 234
2'h5a // 2-digit (8-bit) hexadecimal of value 5A
3'o671 // 3-digit (9-bit) octal of value 671
4b'1x0z // 4-bit binary. 2nd MSB is unknown. LSB is Hi-Z.
3.14 // Floating point
1.28e5 // Scientific notation