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I2C

The I2C interface provides I2C Master functionality. I2C is a two wire serial protocol that allows an I2C Master to exchange data with an I2C Slave. You can use it to communicate with I2C devices such as serial memories, sensors and other modules or integrated circuits.

The I2C protocol supports up to 127 devices per bus, and its default clock frequency is 100KHz.

Warning: Remember that you will need a pull-up resistor on sda and scl.

I2C class reference

Note: The Arm Mbed API uses 8 bit addresses, so make sure to left-shift 7 bit addresses by 1 bit before passing them.

Public Types
enum  RxStatus { NoData, MasterGeneralCall, MasterWrite, MasterRead }
enum  Acknowledge { NoACK = 0, ACK = 1 }
Public Member Functions
 I2C (PinName sda, PinName scl)
void frequency (int hz)
int read (int address, char *data, int length, bool repeated=false)
int read (int ack)
int write (int address, const char *data, int length, bool repeated=false)
int write (int data)
void start (void)
void stop (void)
virtual void lock (void)
virtual void unlock (void)
int transfer (int address, const char *tx_buffer, int tx_length, char *rx_buffer, int rx_length, const event_callback_t &callback, int event=I2C_EVENT_TRANSFER_COMPLETE, bool repeated=false)
void abort_transfer ()
Protected Member Functions
void irq_handler_asynch (void)
void aquire ()
Protected Attributes
event_callback_t _callback
CThunk< I2C_irq
DMAUsage _usage
i2c_t _i2c
int _hz
Static Protected Attributes
static I2C_owner = NULL
static SingletonPtr< PlatformMutex_mutex

I2C hello, world

/* mbed Example Program
 * Copyright (c) 2006-2014 ARM Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#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);
 
        wait(0.5);
 
        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);
    }
}
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