I2C
I2C class hierarchy
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.
Note: Remember that you need a pull-up resistor on sda and scl. All drivers on the I2C bus are required to be open collector, and so it is necessary to use pull-up resistors on the two signals. A typical value for the pull-up resistors is around 2.2k ohms, connected between the pin and 3v3.
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 Member Functions | |
| I2C (PinName sda, PinName scl) | |
| Create an I2C Master interface, connected to the specified pins. More... | |
| I2C (const i2c_pinmap_t &static_pinmap) | |
| Create an I2C Master interface, connected to the specified pins. More... | |
| void | frequency (int hz) |
| Set the frequency of the I2C interface. More... | |
| int | read (int address, char *data, int length, bool repeated=false) |
| Read from an I2C slave. More... | |
| int | read (int ack) |
| Read a single byte from the I2C bus. More... | |
| int | write (int address, const char *data, int length, bool repeated=false) |
| Write to an I2C slave. More... | |
| int | write (int data) |
| Write single byte out on the I2C bus. More... | |
| void | start (void) |
| Creates a start condition on the I2C bus. More... | |
| void | stop (void) |
| Creates a stop condition on the I2C bus. More... | |
| virtual void | lock (void) |
| Acquire exclusive access to this I2C bus. More... | |
| virtual void | unlock (void) |
| Release exclusive access to this I2C bus. More... | |
| 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) |
| Start nonblocking I2C transfer. More... | |
| void | abort_transfer () |
| Abort the ongoing I2C transfer. More... | |
I2C hello, world
/*
* 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);
}
}