86 Family Question:

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;