A beginner's question

[daisyzari]

Can someone help me understand what this code means?

constant CLK_CNT : unsigned(7 downto 0) := conv_unsigned(20, 8);

Thank you :-D

 

[treqer]

constant CLK_CNT <= "00100000";
unclear why so write

 

[shnain]

No it's equivalent to assigning 20 decimal codded on 8 bits:

constant CLK_CNT : unsigned(7 downto 0) := X"14";

or

constant CLK_CNT : unsigned(7 downto 0) := "00010100";

 

[alexan_e]

The function is described The conv_unsigned function

constant CLK_CNT <= "00100000";
unclear why so write

actually the value 20 should be "00010100"

Alex

 

[std_match]

conv_unsigned is not part of the official standard library,
so I recommend to_unsigned instead:

library ieee;
use ieee.numeric_std.all;

constant CLK_CNT : unsigned(7 downto 0) := to_unsigned(20, 8);

 

[alexan_e]

It is part of the std_logic_arith library which is not an IEEE standard library but is still used very often,
so it depends of the libraries that a specific project uses.
to_unsigned can only be used if numeric_std library is used (instead of std_logic_arith)

Alex

 

[daisyzari]

Thank you everyone it has become more clear to us now.