Create pwm.md

docs/en/api/pwm.md

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+# PWM
+
+*PWM used to generate analog signals to drive servos or buzzers,etc.*
+
+## ledcSetup()
+
+**Syntax:**
+
+<mark>void ledcSetup(uint8_t channel, double freq, uint8_t resolution_bits);</mark>
+
+**Description：Set the PWM channel, frequency and resolution.**
+
+## ledcAttachPin()
+
+**Syntax:**
+
+<mark>void ledcAttachPin(uint8_t pin, uint8_t channel);</mark>
+
+**Description：Bind the LEDC channel to the specified IO port to achieve output.**
+
+## ledWrite()
+
+**Syntax：**
+
+<mark>void ledcWrite(uint8_t channel, uint32_t duty);</mark>
+
+**Description：Output waveform to the channel channel according to the specified duty cycle.**
+
+**Example：**
+```arduino
+#include <M5StickC.h>
+int freq = 1800;
+int channel = 0;
+int resolution_bits = 8;
+int buzzer = 2;
+
+void setup() {
+  M5.begin();
+  ledcSetup(channel, freq, resolution_bits);
+  ledcAttachPin(buzzer, channel);
+}
+void loop() {
+    ledcWrite(channel, 128);
+    delay(1000);
+    ledcWrite(channel, 0);
+    delay(1000);
+}
+```