Description: There is a crossroad, whose roads are north-south and east-west, with a set of light-emitting diodes in the south, north, east and west. The lighting laws of traffic signals at this intersection are as follows:
1) in normal circumstances, the two roads take turns. When the signal is converted, according to the rule, it shows:
The vertical and horizontal traffic lights are timed for 60 seconds for red green once, and the remaining time is displayed on the digital tube.
The lights come in three colors: red, yellow and green. Ask to stay in the yellow light for 3 seconds at a time.
The reality of the two roads must ensure that they are crossed.
2) when special vehicles (such as police cars, fire engines, ambulances, etc.) appear on the road, the red lights are displayed on the four sides of the street so that only emergency vehicles can be allowed to pass. Other vehicles are suspended and special vehicles are automatically restored to the original light color.
3) it has the function of changing the light signal in advance, that is, the vehicles on the road can apply for the other way to stop the green light and let it pass. But it's conditional on the fact that it has to be a request for six seconds without a car to respond; The hardware circuit is set to the IRQ1 implementation.
Note that the required time must be obtained through the 8253 timer; Use of 8259 interrupt simulation special car
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