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| ENCODER |
- What are Encoders?
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| General Block Diagram of Encoder |
The digital encoders produce outputs of 2-bit, 3-bit or 4-bit etc., codes depending upon the number of data input lines. An n-bit binary encoder has 2n input lines and n-bit output lines with common types that include 4-to-2, 8-to-3 and 16-to-4 line configurations. The output lines of a digital encoder generate the binary equivalent of the input line whose value is equal to 1 and are available to encode either a decimal or hexadecimal input pattern to typically a binary or B.C.D (binary coded decimal) output code. One of the main disadvantages of standard digital encoders is that they can generate the wrong output code when there is more than one input present at logic level 1. One simple way to overcome this problem is to Prioritise the level of each input pin and if there was more than one input at logic level 1 the actual output code would only correspond to the input with the highest designated priority. Then this type of digital encoder is known commonly as a Priority Encoder.
- 4 by 2 Encoder
IC block
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| IC block |
Truth Table
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| Truth table |
VHDL Code
entity encoder is
port(
D : in STD_LOGIC_VECTOR(3 downto 0);
Q : out STD_LOGIC_VECTOR(1 downto 0)
);
end encoder;
architecture Behavioral of encoder is
begin
process(D) is
begin
case D is
when "0001" => Q <= "00";
when "0010" => Q <= "01";
when "0100" => Q <= "10";
when "1000" => Q <= "11";
when others => Q <= "ZZ";
end case;
end process;
end Behavioral;
Verilog code
module encoder(
output reg [1:0] Q,
input [3:0] D
);
always @(D)
begin
case(D)
4'b0001: Q <= 2'b00;
4'b0010: Q <= 2'b01;
4'b0100: Q <= 2'b10;
4'b1000: Q <= 2'b11;
default: Q <= 2'bzz;
endcase
end
endmodule
Simulation Results
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| Simulation Results |
- 8by3 Encoder
IC Block
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| 8by3 Encoder |
LOGIC DIAGRAM
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| LOGIC's |
Truth Table
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| Truth table |
VHDL Code
entity encoder is
port(
D : in STD_LOGIC_VECTOR(7 downto 0);
Q : out STD_LOGIC_VECTOR(2 downto 0)
);
end encoder;
architecture Behavioral of encoder is
begin
process(D) is
begin
case D is
when "00000001" => Q <= "000";
when "00000010" => Q <= "001";
when "00000100" => Q <= "010";
when "00001000" => Q <= "011";
when "00010000" => Q <= "100";
when "00100000" => Q <= "101";
when "01000000" => Q <= "110";
when "10000000" => Q <= "111";
when others => Q <= "ZZZ";
end case;
end process;
end Behavioral;
Verilog Code
module enc(
output reg [2:0] Q,
input [7:0] D
);
always @(D)
begin
case(D)
8'b00000001: Q <= 3'b000;
8'b00000010: Q <= 3'b001;
8'b00000100: Q <= 3'b010;
8'b00001000: Q <= 3'b011;
8'b00010000: Q <= 3'b100;
8'b00100000: Q <= 3'b101;
8'b01000000: Q <= 3'b110;
8'b10000000: Q <= 3'b111;
default: Q <= 3'bzzz;
endcase
end
endmodule
output reg [2:0] Q,
input [7:0] D
);
always @(D)
begin
case(D)
8'b00000001: Q <= 3'b000;
8'b00000010: Q <= 3'b001;
8'b00000100: Q <= 3'b010;
8'b00001000: Q <= 3'b011;
8'b00010000: Q <= 3'b100;
8'b00100000: Q <= 3'b101;
8'b01000000: Q <= 3'b110;
8'b10000000: Q <= 3'b111;
default: Q <= 3'bzzz;
endcase
end
endmodule
Simulation Results
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| verification phase |
- Priority Encoder
priority encoder is a circuit or algorithm that compresses multiple binary inputs into a smaller number of outputs. The output of a priority encoder is the binary representation of the original number starting from zero of the most significant input bit. They are often used to control interrupt requests by acting on the highest priority encoder. If two or more inputs are given at the same time, the input having the highest priority will take precedence.
IC Block
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| IC for 8by3 priority Encoder |
TRUTH TABLE
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| Truth table |
VHDL Code
entity encoder is
port(
D : in STD_LOGIC_VECTOR(7 downto 0);
Q : out STD_LOGIC_VECTOR(2 downto 0)
);
end encoder;
architecture Behavioral of encoder is
begin
process (D) is
begin
if(D(7) = '1') then
Q <= "111";
elsif(D(6) = '1') then
Q <= "110";
elsif(D(5) = '1') then
Q <= "101";
elsif(D(4) = '1') then
Q <= "100";
elsif(D(3) = '1') then
Q <= "011";
elsif(D(2) = '1') then
Q <= "010";
elsif(D(1) = '1') then
Q <= "001";
elsif(D(0) = '1') then
Q <= "000";
else
Q <= "ZZZ";
end if;
end process;
end Behavioral;
VERILOG Code
module enc(
output reg [2:0] Q,
input [7:0] D
);
always @(D)
begin
if(D[7] == 1'b1)
Q <= 3'b111;
else if(D[6] == 1'b1)
Q <= 3'b110;
else if(D[5] == 1'b1)
Q <= 3'b101;
else if(D[4] == 1'b1)
Q <= 3'b100;
else if(D[3] == 1'b1)
Q <= 3'b011;
else if(D[2] == 1'b1)
Q <= 3'b010;
else if(D[1] == 1'b1)
Q <= 3'b001;
else if(D[0] == 1'b1)
Q <= 3'b000;
else
Q <= 3'bzzz;
end
endmodule
Simulation Results
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| verification |
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