VHDL Hex Values?

Question

How do I write hex numbers in VHDL?

Answer 1

VHDL Hex Values

Quick Syntax

Hex in VHDL for 8-bits: x"00"

signal my_slv : std_logic_vector(7 downto 0) := x"1F";

........

my_slv <= x"0A";

Purpose

Hex is a 16 based math system. Therefore, you can have these values:

Decimal => Hex:

0 => 0
1 => 1
2 => 2
3 => 3
4 => 4
5 => 5
6 => 6
7 => 7
8 => 8
9 => 9
10 => A
11 => B
12 => C
13 => D
14 => E
15 => F

In VHDL, hex is a much easier way to set bigger vectors instead of regular binary. This is because one symbol of hex is 4-bits of binary. For example:

signal my_slv : std_logic_vector(15 downto 0);

-- binary method
my_slv <= "0000000000000001";

-- hex method
my_slv <= x"0001";

You can also mix binary and hex for uneven 4-bit vectors:

signal my_slv : std_logic_vector(9 downto 0);

-- mixed method
my_slv <= "00" & x"01";