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Verilog HDL Syntax And Semantics Part-II

Saturday, 11 September 2021 13:53 Semicon Editor 01

Numbers in Verilog

You can specify constant numbers in decimal, hexadecimal, octal, or binary format. Negative numbers are represented in 2's complement form.

When used in a number, the question mark (?) character is the Verilog alternative for the z character. The underscore character (_) is legal anywhere in a number except as the first character, where it is ignored.

Integer Numbers

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Verilog HDL allows integer numbers to be specified as

.

Sized or unsized numbers (Unsized size is 32 bits)
In a radix of binary, octal, decimal, or hexadecimal
Radix and hex digits (a,b,c,d,e,f) are case insensitive
Spaces are allowed between the size, radix and value

Syntax: ';

Example of Integer Numbers

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Integer	Stored as
1	00000000000000000000000000000001
8'hAA	10101010
6'b10_0011	100011
'hF	00000000000000000000000000001111

Verilog expands filling the specified by working from right-to-left

When is smaller than , then leftmost bits of are truncated
When is larger than , then leftmost bits are filled, based on the value of the leftmost bit in .
Leftmost '0' or '1' are filled with '0'
Leftmost 'Z' are filled with 'Z'
Leftmost 'X' are filled with 'X'

Note : X Stands for unknown and Z stands for high impedance, 1 for logic high or 1 and 0 for logic low or 0.

Example of Integer Numbers

Integer	Stored as
6'hCA	001010
6'hA	001010
16'bZ	ZZZZZZZZZZZZZZZZ
8'bx	xxxxxxxx

Real Numbers

Verilog supports real constants and variables
Verilog converts real numbers to integers by rounding
Real Numbers can not contain 'Z' and 'X'
Real numbers may be specified in either decimal or scientific notation
.
E
Real numbers are rounded off to the nearest integer when assigning to an integer

Example of Real Numbers

Real Number	Decimal notation
1.2	1.2
0.6	0.6
3.5E6	3,500000.0

Signed and Unsigned Numbers
Verilog Supports both types of numbers, but with certain restrictions. Like in C language we don't have int and unint types to say if a number is signed integer or unsigned integer.

Any number that does not have negative sign prefix is a positive number. Or indirect way would be "Unsigned".

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Negative numbers can be specified by putting a minus sign before the size for a constant number, thus they become signed numbers. Verilog internally represents negative numbers in 2's complement format. An optional signed specifier can be added for signed arithmetic

Examples