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;

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;

5234

---

How does the size of PMOS Pull Up transistors (for bit & bit- lines) affect SRAM's performance?

1186

---

If the current through the poly is 20nA and the contact can take a max current of 10nA how would u overcome the problem?

1073

---

Explain the Working of a 2-stage OPAMP?

1149

---

Explain depletion region.

990

---

what is verilog?

1072

---

Describe the various effects of scaling?

4751

---

Draw Vds-Ids curve for a MOSFET. Now, show how this curve changes considering Channel Length Modulation.

1158

---

What was your role in the silicon evaluation/product ramp? What tools did you use?

3664

---

Explain how MOSFET works?

3201

---

what is a sequential circuit?

1107

---

Why does the present vlsi circuits use mosfets instead of bjts?

1240

---

Differences between Array and Booth Multipliers?

4025

---

What are the different design techniques required to create a layout for digital circuits?

1013

---

What are the different measures that are required to achieve the design for better yield?

1183

---