Include 1-Wire sensor example for DS18B20

sites/en/docs/Sensor/SeeedStudio_XIAO/SeeedStudio_XIAO_SAMD21/Seeeduino-XIAO.md

@@ -355,6 +355,108 @@ void loop()
 
 <p style={{textAlign: 'center'}}><img src="https://files.seeedstudio.com/wiki/Seeeduino-XIAO/img/THonny_DAC.jpg" alt="pir" width={600} height="auto" /></p>
 
+#### 1-Wire
+
+In this example Dallas/Maxim DS18B20 sensor connected to the line DA2.
+
+```cpp
+#include <Arduino.h>
+
+#define OW_PIN 2
+
+// Bus control
+void    ow_low()  { pinMode(OW_PIN, OUTPUT); digitalWrite(OW_PIN, LOW); }
+void    ow_rel()  { pinMode(OW_PIN, INPUT); }
+int     ow_rd()   { return digitalRead(OW_PIN); }
+
+bool ow_reset() {
+    ow_low(); delayMicroseconds(480);
+    ow_rel(); delayMicroseconds(70);
+    bool p = !ow_rd();
+    delayMicroseconds(410);
+    return p;
+}
+
+void ow_write_bit(uint8_t b) {
+    ow_low(); delayMicroseconds(b ? 6 : 60);
+    ow_rel(); delayMicroseconds(b ? 64 : 10);
+}
+
+uint8_t ow_read_bit() {
+    ow_low(); delayMicroseconds(6);
+    ow_rel(); delayMicroseconds(9);
+    uint8_t b = ow_rd();
+    delayMicroseconds(55);
+    return b;
+}
+
+void    ow_write(uint8_t v)  { for(int i=0;i<8;i++) ow_write_bit((v>>i)&1); }
+
+uint8_t ow_read_byte()       { uint8_t v=0; for(int i=0;i<8;i++) v|=ow_read_bit()<<i; return v; }
+
+uint8_t crc8(uint8_t *d, uint8_t len) {
+    uint8_t crc=0;
+    for(uint8_t i=0;i<len;i++) {
+        uint8_t b=d[i];
+        for(uint8_t j=0;j<8;j++) { uint8_t m=(crc^b)&1; crc>>=1; if(m) crc^=0x8C; b>>=1; }
+    }
+    return crc;
+}
+
+void print_hex(uint8_t *d, uint8_t len) {
+    for(int i=0;i<len;i++) { if(d[i]<0x10) Serial.print("0"); Serial.print(d[i],HEX); if(i<len-1) Serial.print(" "); }
+}
+
+void setup() {
+    Serial.begin(115200);
+    while(!Serial) delay(10);
+    pinMode(OW_PIN, INPUT);
+}
+
+void loop() {
+    uint8_t rom[8], scratch[9];
+
+    Serial.print("\n[RESET] ");
+    if(!ow_reset()) { Serial.println("NO"); delay(2000); return; }
+    Serial.println("YES");
+
+    // Read ROM (single device only)
+    ow_write(0x33);
+    for(int i=0;i<8;i++) rom[i]=ow_read_byte();
+    Serial.print("[ROM]   "); print_hex(rom,8);
+    Serial.println(crc8(rom,8)==0 ? (rom[0]==0x28 ? "  = DS18B20" : "  UNKNOWN") : "  CRC FAIL");
+
+    // Start conversion with strong pull-up for parasitic power
+    ow_reset();
+    ow_write(0xCC); ow_write(0x44);
+    pinMode(OW_PIN, OUTPUT); digitalWrite(OW_PIN, HIGH);
+    delay(750);
+    ow_rel();
+
+    // Read scratchpad
+    ow_reset();
+    ow_write(0xCC); ow_write(0xBE);
+    for(int i=0;i<9;i++) scratch[i]=ow_read_byte();
+    Serial.print("[DATA]  "); print_hex(scratch,9);
+    if(crc8(scratch,9)!=0) { Serial.println("  CRC FAIL"); delay(2000); return; }
+
+    // Decode temperature (12-bit signed, 0.0625°C/LSB)
+    int16_t raw = (scratch[1]<<8)|scratch[0];
+    Serial.print("  OK\n[TEMP]  ");
+    Serial.print(raw/16.0f, 2);
+    Serial.println(" °C");
+    delay(2000);
+}
+```  
+
+Result:
+```
+[RESET] YES  
+[ROM]   28 FF 14 DA 81 15 01 B5  = DS18B20  
+[DATA]  BA 01 7D C9 7F FF 7F 10 2F  OK  
+[TEMP]  27.62 °C  
+```
+
 ## Getting Started
 
 ### Hardware