Adding Hex numbers

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Hi,

Does anyone know how can I add Hex numbers inside the process (VHDL)?

For instance, I want to add x"55" + x"55" but if I'll write " x"55" or x"55" " the answer will be x"55" (the answer should be x"AA").

Idan

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Of course x"55" or x"55" is x"55" as this is a binary or, used on the vector bitwise.

Addition in VHDL (one of the reasons I prefer Verilog over HDL) requires type conversions as it has quite a strict type checking:

result <= std_logic_vector(unsigned(x"55") + unsigned(x"55"));

Also please note that unless you do know exactly what you do an addition of two vectors with N and M bits require the result to be max(N,M) + 1 bit wide.

I want to add two hex numbers inside the process…

This is my code:

"

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

--USE IEEE.STD_LOGIC_ARITH.ALL;

USE IEEE.STD_LOGIC_UNSIGNED.ALL;

USE IEEE.NUMERIC_STD.ALL; --I using "conv_std_logic_vector" function

…

signal TX_checkSum: std_logic_vector (8 downto 0);

begin

process (clk)

begin

if reset='1' then

…

elsif clk'event and clk='1' then

TX_checkSum <= std_logic_vector(unsigned(x"55") + unsigned(x"55"));

end if;

end process; "

I get the following error:" Error (10408): VHDL error at UART.vhd(139): can't determine type of object at or near string ""01010101"" -- found 25 possible types".

What could be the problem?