Abstract : This paper analyzes the characteristics of the 8255A and 8253 chips and uses their features to design a traffic light simulation system. After elaborating on the design concept and circuit design scheme, effectiveness tests on the system show that the traffic light simulation system has relatively reliable performance and has certain reference value for related electronic designs. Finally, the author looks forward to the future development of electronic design, believing that traffic control lights will play a greater role in future industry applications.
Keywords : Programmable controller; traffic lights; analog system; electronic design
1. Requirements Analysis
The design of this system first requires understanding the on/off pattern of traffic lights. Consider a crossroads: intersections 1 and 3 represent north and south, respectively, while intersections 2 and 4 represent east and west. Initially, all four intersections have red lights on. Then, the green lights at intersections 1 and 3 turn on, while the red lights at intersections 2 and 4 turn on, allowing traffic to pass through intersections 1 and 3. After a delay, the green lights at intersections 1 and 3 turn off, and their yellow lights begin to flash. After flashing several times, the red lights at intersections 1 and 3 turn on, and simultaneously, the green lights at intersections 2 and 4 turn on, allowing traffic to pass through intersections 2 and 4. After another delay, the green lights at intersections 2 and 4 turn off, and their yellow lights begin to flash. After flashing several times, the lights then switch back to those at intersections 1 and 3.
Then, repeat the above process. For the on/off state of each group of lights, we used the input/output functions of the 8255A.
2. Time control scheme for each group of lights turning on and off.
A. Use software-program to control the time delay. Features of this scheme: Software timing is the simplest timing method. It does not require hardware support. Just let the machine execute a certain instruction or a series of instructions in a loop. These instructions themselves do not have a specific execution purpose. However, since each instruction takes a certain amount of time to execute, repeatedly executing these instructions will occupy a fixed period of time. Therefore, this delay method is conventionally called software delay. By correctly selecting instructions and changing the timing time, it is flexible, convenient, and cost-effective. The obvious disadvantage of this method is that the CPU utilization rate is too low. During the specified loop period, the CPU cannot do any other useful work. Instead, it just loops repeatedly, waiting for the predetermined timing time to arrive. In many cases, this is not allowed [1]. For example, the timed refresh operation of dynamic memory needs to be continuously performed as long as the machine is powered on. Obviously, software delay cannot be used.
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