GPIO是什么？

悠悠 2022-10-15 11:58 136阅读 0赞

**GPIO**（英语：General-purpose input/output），通用型之输入输出的简称，功能类似8051的P0—P3，其接脚可以供[使用者][Link 1]由程控自由使用，PIN脚依现实考量可作为通用输入（*GPI*）或通用输出（*GPO*）或通用输入与输出（*GPIO*），如当clk generator, chip select等。

既然一个[引脚][Link 2]可以用于输入、输出或其他特殊功能，那么一定有[寄存器][Link 3]用来选择这些功能。对于输入，一定可以通过读取某个寄存器来确定引脚电位的高低；对于输出，一定可以通过写入某个寄存器来让这个引脚输出高电位或者低电位；对于其他特殊功能，则有另外的寄存器来控制它们。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2N3X2h1YW5n_size_16_color_FFFFFF_t_70][]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2RwamNuMTk5MA_size_16_color_FFFFFF_t_70]

#include <ESP8266WiFi.h>
    
    // 填上自己的wifi账号和密码
    const char* ssid     = "REPLACE_WITH_YOUR_SSID";
    const char* password = "REPLACE_WITH_YOUR_PASSWORD";
    
    // Set web server port number to 80
    WiFiServer server(80);
    
    // Variable to store the HTTP request
    String header;
    
    // Auxiliar variables to store the current output state
    String output5State = "off";
    String output4State = "off";
    
    // Assign output variables to GPIO pins
    const int output5 = 5;
    const int output4 = 4;
    
    // Current time
    unsigned long currentTime = millis();
    // Previous time
    unsigned long previousTime = 0; 
    // Define timeout time in milliseconds (example: 2000ms = 2s)
    const long timeoutTime = 2000;
    
    void setup() {
      Serial.begin(115200);
      // Initialize the output variables as outputs
      pinMode(output5, OUTPUT);
      pinMode(output4, OUTPUT);
      // Set outputs to LOW
      digitalWrite(output5, LOW);
      digitalWrite(output4, LOW);
    
      // Connect to Wi-Fi network with SSID and password
      Serial.print("Connecting to ");
      Serial.println(ssid);
      WiFi.begin(ssid, password);
      while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
      }
      // Print local IP address and start web server
      Serial.println("");
      Serial.println("WiFi connected.");
      Serial.println("IP address: ");
      Serial.println(WiFi.localIP());
      server.begin();
    }
    
    void loop(){
      WiFiClient client = server.available();   // Listen for incoming clients
    
      if (client) {                             // If a new client connects,
        Serial.println("New Client.");          // print a message out in the serial port
        String currentLine = "";                // make a String to hold incoming data from the client
        currentTime = millis();
        previousTime = currentTime;
        while (client.connected() && currentTime - previousTime <= timeoutTime) { // loop while the client's connected
          currentTime = millis();         
          if (client.available()) {             // if there's bytes to read from the client,
            char c = client.read();             // read a byte, then
            Serial.write(c);                    // print it out the serial monitor
            header += c;
            if (c == '\n') {                    // if the byte is a newline character
              // if the current line is blank, you got two newline characters in a row.
              // that's the end of the client HTTP request, so send a response:
              if (currentLine.length() == 0) {
                // HTTP headers always start with a response code (e.g. HTTP/1.1 200 OK)
                // and a content-type so the client knows what's coming, then a blank line:
                // 拼接HTTP协议回复
                client.println("HTTP/1.1 200 OK");
                client.println("Content-type:text/html");
                client.println("Connection: close");
                client.println();
                
                // turns the GPIOs on and off
                if (header.indexOf("GET /5/on") >= 0) {
                  Serial.println("GPIO 5 on");
                  output5State = "on";
                  digitalWrite(output5, HIGH);
                } else if (header.indexOf("GET /5/off") >= 0) {
                  Serial.println("GPIO 5 off");
                  output5State = "off";
                  digitalWrite(output5, LOW);
                } else if (header.indexOf("GET /4/on") >= 0) {
                  Serial.println("GPIO 4 on");
                  output4State = "on";
                  digitalWrite(output4, HIGH);
                } else if (header.indexOf("GET /4/off") >= 0) {
                  Serial.println("GPIO 4 off");
                  output4State = "off";
                  digitalWrite(output4, LOW);
                }
                
                // Display the HTML web page
                client.println("<!DOCTYPE html><html>");
                client.println("<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">");
                client.println("<link rel=\"icon\" href=\"data:,\">");
                // CSS to style the on/off buttons 
                // Feel free to change the background-color and font-size attributes to fit your preferences
                client.println("<style>html { font-family: Helvetica; display: inline-block; margin: 0px auto; text-align: center;}");
                client.println(".button { background-color: #195B6A; border: none; color: white; padding: 16px 40px;");
                client.println("text-decoration: none; font-size: 30px; margin: 2px; cursor: pointer;}");
                client.println(".button2 {background-color: #77878A;}</style></head>");
                
                // Web Page Heading
                client.println("<body><h1>ESP8266 Web Server</h1>");
                
                // Display current state, and ON/OFF buttons for GPIO 5  
                client.println("<p>GPIO 5 - State " + output5State + "</p>");
                // If the output5State is off, it displays the ON button       
                if (output5State=="off") {
                  client.println("<p><a href=\"/5/on\"><button class=\"button\">ON</button></a></p>");
                } else {
                  client.println("<p><a href=\"/5/off\"><button class=\"button button2\">OFF</button></a></p>");
                } 
                   
                // Display current state, and ON/OFF buttons for GPIO 4  
                client.println("<p>GPIO 4 - State " + output4State + "</p>");
                // If the output4State is off, it displays the ON button       
                if (output4State=="off") {
                  client.println("<p><a href=\"/4/on\"><button class=\"button\">ON</button></a></p>");
                } else {
                  client.println("<p><a href=\"/4/off\"><button class=\"button button2\">OFF</button></a></p>");
                }
                client.println("</body></html>");
                
                // The HTTP response ends with another blank line
                client.println();
                // Break out of the while loop
                break;
              } else { // if you got a newline, then clear currentLine
                currentLine = "";
              }
            } else if (c != '\r') {  // if you got anything else but a carriage return character,
              currentLine += c;      // add it to the end of the currentLine
            }
          }
        }
        // Clear the header variable
        header = "";
        // Close the connection
        client.stop();
        Serial.println("Client disconnected.");
        Serial.println("");
      }
    }

代码中的 4和5是指的GPIO的引脚号。

[Link 1]: https://baike.baidu.com/item/%E4%BD%BF%E7%94%A8%E8%80%85/1162412
[Link 2]: https://baike.baidu.com/item/%E5%BC%95%E8%84%9A/10879873
[Link 3]: https://baike.baidu.com/item/%E5%AF%84%E5%AD%98%E5%99%A8/187682
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