Answer Posted / seetharamukg

Signals updates a value after some "delta" time or at the
end of the process. But variable updates a value immediately.

Both variable and signals are synthesizable.
Designer should know hoe to use these 2 objects.

Ex: Signal usage
Library IEEE;
use IEEE.std_logic_1164.all;
entity xor_sig is
port (
A, B, C: in STD_LOGIC;
X, Y: out STD_LOGIC
);
end xor_sig;
architecture SIG_ARCH of xor_sig is
signal D: STD_LOGIC;
begin
SIG:process (A,B,C)
begin
D <= A; -- ignored !!
X <= C xor D;
D <= B; -- overrides !!
Y <= C xor D;
end process;
end SIG_ARCH;

Variable usage:
Library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
entity xor_var is
port (
A, B, C: in STD_LOGIC;
X, Y: out STD_LOGIC
);
end xor_var;
architecture VAR_ARCH of xor_var is
begin
VAR:process (A,B,C)
variable D: STD_LOGIC;
begin
D := A;
X <= C xor D;
D := B;
Y <= C xor D;
end process;
end VAR_ARCH;

Draw a transistor level two input NAND gate. Explain its sizing (a) considering Vth (b) for equal rise and fall times

1716

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Explain what is Verilog?

1156

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Explain Cross section of an NMOS transistor?

1072

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For f = AB+CD if B is S-a-1, what are the test vectors needed to detect the fault?

1298

---

what is the difference between the TTL chips and CMOS chips?

1166

---

What is Charge Sharing? Explain the Charge Sharing problem while sampling data from a Bus

1316

---

Explain the operation of a 6T-SRAM cell?

4570

---

Need to convert this VHDL code into VLSI verilog code? LIBRARY IEEE; USE IEEE.STD_LOGIC_1164.ALL; ----using all functions of specific package--- ENTITY tollbooth2 IS PORT (Clock,car_s,RE : IN STD_LOGIC; coin_s : IN STD_LOGIC_VECTOR(1 DOWNTO 0); r_light,g_light,alarm : OUT STD_LOGIC); END tollbooth2; ARCHITECTURE Behav OF tollbooth2 IS TYPE state_type IS (NO_CAR,GOTZERO,GOTFIV,GOTTEN,GOTFIF,GOTTWEN,CAR_PAID,CHEATE D); ------GOTZERO = PAID $0.00--------- ------GOTFIV = PAID $0.05---------- ------GOTTEN = PAID $0.10---------- ------GOTFIF = PAID $0.15---------- ------GOTTWEN = PAID $0.20--------- SIGNAL present_state,next_state : state_type; BEGIN -----Next state is identified using present state,car & coin sensors------ PROCESS(present_state,car_s,coin_s) BEGIN CASE present_state IS WHEN NO_CAR => IF (car_s = '1') THEN next_state <= GOTZERO; ELSE next_state <= NO_CAR; END IF; WHEN GOTZERO => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTZERO; ELSIF (coin_s = "01") THEN next_state <= GOTFIV; ELSIF (coin_s ="10") THEN next_state <= GOTTEN; END IF; WHEN GOTFIV=> IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTFIV; ELSIF (coin_s = "01") THEN next_state <= GOTTEN; ELSIF (coin_s <= "10") THEN next_state <= GOTFIV; END IF; WHEN GOTTEN => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s ="00") THEN next_state <= GOTTEN; ELSIF (coin_s="01") THEN next_state <= GOTFIV; ELSIF (coin_s="10") THEN next_state <= GOTTWEN; END IF; WHEN GOTFIF => IF (car_s ='0') THEN next_state <= CHEATED; ELSIF (coin_s = "00") THEN next_state <= GOTFIF; ELSIF (coin_s ="01") THEN next_state <= GOTTWEN; ELSIF (coin_s = "10") THEN next_state <= GOTTWEN; END IF; WHEN GOTTWEN => next_state <= CAR_PAID; WHEN CAR_PAID => IF (car_s = '0') THEN next_state <= NO_CAR; ELSE next_state<= CAR_PAID; END IF; WHEN CHEATED => IF (car_s = '1') THEN next_state <= GOTZERO; ELSE next_state <= CHEATED; END IF; END CASE; END PROCESS;-----End of Process 1 -------PROCESS 2 for STATE REGISTER CLOCKING-------- PROCESS(Clock,RE) BEGIN IF RE = '1' THEN present_state <= GOTZERO; ----When the clock changes from low to high,the state of the system ----stored in next_state becomes the present state----- ELSIF Clock'EVENT AND Clock ='1' THEN present_state <= next_state; END IF; END PROCESS;-----End of Process 2------- --------------------------------------------------------- -----Conditional signal assignment statements---------- r_light <= '0' WHEN present_state = CAR_PAID ELSE '1'; g_light <= '1' WHEN present_state = CAR_PAID ELSE '0'; alarm <= '1' WHEN present_state = CHEATED ELSE '0'; END Behav;

5328

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What is Noise Margin? Explain the procedure to determine Noise Margin?

2511

---

Explain how MOSFET works?

3294

---

How do you size NMOS and PMOS transistors to increase the threshold voltage?

3086

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Explain what is the use of defpararm?

1192

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You have three adjacent parallel metal lines. Two out of phase signals pass through the outer two metal lines. Draw the waveforms in the centre metal line due to interference. Now, draw the signals if the signals in outer metal lines are in phase with each other

1615

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What types of CMOS memories have you designed? What were their size? Speed?

4702

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What products have you designed which have entered high volume production?

2487

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