The block diagram for an elevator controller for a building with two floors is shown in the following diagram. The inputs FB₁and FB₂are floor buttons in the elevator. The inputs CALL₁and CALL₂are call buttons in the hall. The inputs FS₁and FS₂are floor switches that output a 1 when the elevator is at the first or second floor landing. Outputs UP and DOWN control the motor, and the elevator is stopped when UP = DOWN = 0. N₁and N₂are flip-flops that indicate when the elevator is needed on the first or second floor. R₁and R₂are signals that reset these flip-flops. DO = 1 causes the door to open, and DC = 1 indicates that the door is closed. Draw an SM chart for the elevator controller (four states).

R2 FB, Storage circuit N1 R1 CALL, - FB2 Storage Elevator + UP control circuit N2 CALL2 + DOWN circuit FS, FS2 DO Door mechanism DC