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How to create if else statement for VHDL

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pearl87

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how to create a if else statement when the statement i as below...
if a>b.c
{P='0110';
D='0000'
eleseif c>b>a
P='0110';
D='1111"
eleseif b>c>a
P='0110';
D='0000'
else a=b=c
P='0000'
D='0000'


library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity comparator is
port( a, b, c : in std_logic_vector( 6 downto 0); --
p, D : out std_logic_vector( 3 downto 0));
end comparator;

architecture processing of comparator is

begin
process (a, b, c)
begin
if (a=> b)
then p<='1';
else
p<='0';
end if;
end process;
end architecture processing;


i try to do but dunno what is the problem as i am still new to VHDL codings... please do help me as i need to do this assignment
 

Code: 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;

entity comparator is
port( a, b, c : in std_logic_vector( 6 downto 0); --
p, D : out std_logic_vector( 3 downto 0));
end comparator;

architecture processing of comparator is

begin
process (a, b, c)

begin
	if ([B]a <= b[/B]) then 
		p<=[B]"0001"[/B];
	else
		p<=[B]"0000"[/B];
	end if;
end process;

end architecture processing;

Bigger than or equal is written >=
P is a 4 bit vector, you can't assign a bit value to it.

Alex
 
to Mr Alex,
thanks for the help and I am still wondering can i compare 3 input together "a>b>c".... and give 2 output data 4 bit...
 

When you are working with vector and you want to write only one or more bits you can use:
for p in your example

p : out std_logic_vector( 3 downto 0);

p(3)<='1'; -- assign only bit 3 with value 1
p(0)<='0'; -- assign only bit 0 with value 0
p(3 down to 2)<= "01"; -- assign bits 3 and 2 with value 01 (partial assignment)
p(2 down to 0)<= "001"; -- assign bits 2,1 and 0 with value 001

Alex

---------- Post added at 17:26 ---------- Previous post was at 17:24 ----------

You can break it in 2 parts

if ((a>b) and (b>c)) then
set value here
set value here
else
do something
do something more
end if;
 
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