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Altera_Forum's avatar
Altera_Forum
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13 years ago

offset binary to signed converter for ADC

Hello

I’m neebie in VHDL. I’m trying to build a simple radio receiver: CAN , mult, filter, I Q demod in Cyclone III , with quartus . I ‘m sorry for this question here, be I don’t found solution, after many searches. I’d like to convert the input data from CAN (offset binary) to signed value. Very common issue...At the end I’d like to do the conversion from signed to offset inary .

Thus I try next code ( only on 3 bits for investigation purpose). Compilation ok, building component ok , starting simulation Ok ; but result Is the same as input…I ‘ don’t understand. Many thanks for your help.

LIBRARY ieee;

USE ieee.std_logic_1164.all;

USE ieee.std_logic_arith.all;

ENTITY convsign IS

PORT (op1 : IN UNSIGNED(2 DOWNTO 0);

resu : OUT SIGNED(2 DOWNTO 0));

END convsign;

ARCHITECTURE cpcvsign OF convsign IS

BEGIN

resu <= CONV_SIGNED(op1, 3);

END cpcvsign;

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    To convert offset binary to signed, just invert sign bit, nothing else

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    Invert the sign bit is the solution i use with logical gates, before my investigation on CONV_SIGNED fnction.

    I stop trying to understand convert function. I keep the basic solution in vhdl :

    library IEEE;

    use IEEE.STD_LOGIC_1164.ALL;

    use IEEE.STD_LOGIC_ARITH.ALL;

    use IEEE.STD_LOGIC_UNSIGNED.ALL;

    ENTITY INVBITBUS IS

    PORT(

    a_bus : IN bit_vector(2 downto 0);

    s_bus : OUT bit_vector(2 downto 0));

    SIGNAL a, b ,c : BIT;

    END INVBITBUS ;

    ARCHITECTURE dataflow OF INVBITBUS IS

    BEGIN

    a <= a_bus(2);

    b <= a_bus(1);

    c <= a_bus(0);

    s_bus (2) <= NOT (a);

    s_bus (1) <= b;

    s_bus (0) <= c;

    END dataflow ;
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    As most problems, it can be solved in one line. VHDL-wise, the conversion can be most easily done as a XOR operation with an inversion mask.

    data2 <= data1 XOR x"800"; -- for 12 Bit data
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    hello

    as most problem , there many solutions..here is mine , simplier for 14 bits than the previous i have done....interresting for partial bus allocation.

    ENTITY INVBITBUS14 IS

    PORT(

    a_bus : IN bit_vector(13 downto 0);

    s_bus : OUT bit_vector(13 downto 0));

    SIGNAL a13 : BIT;

    END INVBITBUS14 ;

    ARCHITECTURE dataflow OF INVBITBUS14 IS

    BEGIN

    a13 <= a_bus(13);

    s_bus (13) <= NOT (a13); -- inversion du bit

    s_bus(12 DOWNTO 0) <= a_bus(12 DOWNTO 0);

    END dataflow ;

    Many thanks for your help!!!!!!!!