add I2C example

APIs_Drivers/I2C_ex_1/README.md

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+# I2C example
+
+This example shows how to use `I2C` API to read temperature sensor. The Mbed OS `I2C` API uses 8 bit addressing and will auto append the 0 or 1 for read/write mode. Please keep in mind that every I2C set up has its own quirks so this example may not work out of the box for your sensor / application. Make sure to check the data sheet for your part for the timing / register access specification.

APIs_Drivers/I2C_ex_1/main.cpp

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+/*
+ * Copyright (c) 2014-2020 Arm Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "mbed.h"
+
+// Read temperature from LM75BD
+
+I2C i2c(I2C_SDA, I2C_SCL);
+
+const int addr7bit = 0x48;      // 7 bit I2C address
+const int addr8bit = 0x48 << 1; // 8bit I2C address, 0x90
+
+int main()
+{
+    char cmd[2];
+    while (1) {
+        cmd[0] = 0x01;
+        cmd[1] = 0x00;
+        i2c.write(addr8bit, cmd, 2);
+
+        ThisThread::sleep_for(500);
+
+        cmd[0] = 0x00;
+        i2c.write(addr8bit, cmd, 1);
+        i2c.read(addr8bit, cmd, 2);
+
+        float tmp = (float((cmd[0] << 8) | cmd[1]) / 256.0);
+        printf("Temp = %.2f\n", tmp);
+    }
+}