说明：  no intro
((1) to show intersections east and west in both directions of the red, yellow, green indicates the state • Use two sets of red, yellow, and green lights as the two directions of red, yellow, green, countdown to achieve normal function • Digital control with two north-south direction as to the things and time display, time display a red light 55 seconds, 50 seconds green, yellow 5 seconds * (2) Press the S1 key, to achieve a special state function: • Display to the timing of the two sets of digital flash • The counter stops counting and remains in its original state • east and west, crossing all red light status • Special lifting of the state can continue to count. (3) to achieve the overall SB Clear function key pressed, the system achieved a total cleared, the counter counts from the initial state, the corresponding status indicator light (4) using VHDL language design meets the functional requirements of the traffic light co)