State Machine Design: The Electric Train Controller - Rapid Prototyping of Digital Systems - page 156

WHEN "10" => state <= Ain;
WHEN "11" => state <= Ain;
-- Default case is always required
WHEN OTHERS => state <= ABout;
END CASE ;
WHEN Ain =>
CASE Sensor24 IS
WHEN "00" => state <= Ain;
WHEN "01" => state <= ABout;
WHEN "10" => state <= Bstop;
WHEN "11" => state <= ABout;
WHEN OTHERS => state <= ABout;
END CASE ;
WHEN Bin =>
CASE Sensor13 IS
WHEN "00" => state <= Bin;
WHEN "01" => state <= ABout;
WHEN "10" => state <= Astop;
WHEN "11" => state <= About;
WHEN OTHERS => state <= ABout;
END CASE ;
WHEN Astop =>
IF Sensor3 = '1' THEN
state <= Ain;
ELSE
state <= Astop;
END IF ;
WHEN Bstop =>
IF Sensor4 = '1' THEN
state <= Bin;
ELSE
state <= Bstop;
END IF ;
END CASE ;
END IF ;
END PROCESS ;
-- combine sensor bits for case statements above
-- "&" operator combines bits
sensor12 <= sensor1 & sensor2;
sensor13 <= sensor1 & sensor3;
sensor24 <= sensor2 & sensor4;
-- These outputs do not depend on the state
Switch3 <= '0';