I2CSlave Class Reference

An I2C Slave, used for communicating with an I2C Master device. More...

#include <I2CSlave.h>

Public Member Functions
	I2CSlave (PinName sda, PinName scl)
	Create an I2C Slave interface, connected to the specified pins. More...
	I2CSlave (const i2c_pinmap_t &static_pinmap)
	Create an I2C Slave interface, connected to the specified pins. More...
void	frequency (int hz)
	Set the frequency of the I2C interface. More...
int	receive (void)
	Check if this I2C Slave has been addressed. More...
int	read (char *data, int length)
	Read bytes transmitted to this MCU from an I2C master. More...
int	read (void)
	Read a single byte from an I2C master. More...
int	write (const char *data, int length)
	Write to an I2C master which is addressing this slave device. More...
int	write (int data)
	Write a single byte to an I2C master. More...
void	address (int address)
	Set the I2C slave address. More...
void	stop (void)
	Reset the I2C slave back into the known ready receiving state. More...

Detailed Description

An I2C Slave, used for communicating with an I2C Master device.

Note

Synchronization level: Not protected

Example Simple I2C slave and master (requires two Mbed-boards):

#include <mbed.h>
#include <mbed_wait_api.h>
#include <string.h>
 
#define BUILD_I2C_SLAVE 1 // Build for slave or master of this example
 
#define SLAVE_ADDR 0xA0
#define BUFFER_SIZE 6
 
#if BUILD_I2C_SLAVE
 
// Slave side of the example
 
#if !DEVICE_I2CSLAVE
#error [NOT_SUPPORTED] I2C Slave is not supported
#endif
 
I2CSlave slave(I2C_SDA, I2C_SCL);
 
int main() {
 
    char buf[BUFFER_SIZE] = "ABCDE";
 
    slave.address(SLAVE_ADDR);
    while (1) {
        int i = slave.receive();
        switch (i) {
            case I2CSlave::ReadAddressed:
                // Write back the buffer from the master
                slave.write(buf, BUFFER_SIZE);
                printf("Written to master (addressed): %s\n", buf);
                break;
 
            case I2CSlave::WriteGeneral:
                slave.read(buf, BUFFER_SIZE);
                printf("Read from master (general): %s\n", buf);
                break;
 
            case I2CSlave::WriteAddressed:
                slave.read(buf, BUFFER_SIZE);
                printf("Read from master (addressed): %s\n", buf);
                break;
        }
    }
}
 
#else
 
// Master side of the example
 
I2C master(I2C_SDA, I2C_SCL);
 
static const char* to_send[] = { "abcde", "12345", "EFGHI" };
 
int main() {
    char buf[BUFFER_SIZE];
    int send_index = 0;
 
    while (1) {
        strcpy(buf, to_send[send_index]);
 
        // Write the new message to the slave
        if (master.write(SLAVE_ADDR, buf, BUFFER_SIZE)) {
            printf("Failed to write to slave!\n");
        } else {
            printf("Written to slave: %s\n", buf);
        }
 
        // Read what the slave has (should be identical)
        if (master.read(SLAVE_ADDR, buf, BUFFER_SIZE)) {
            printf("Failed to read from slave!\n");
        } else {
            printf("Read from slave: %s\n", buf);
        }
 
        // Change the message we're writing to the slave
        send_index++;
        if (send_index > 2) {
            send_index = 0;
        }
 
        wait_us(500000); // Wait 0.5s
    }
}
 
#endif

Definition at line 128 of file I2CSlave.h.

Constructor & Destructor Documentation

I2CSlave() [1/2]

I2CSlave	(	PinName	sda,
		PinName	scl
	)

Create an I2C Slave interface, connected to the specified pins.

Parameters

sda	I2C data line pin.
scl	I2C clock line pin.

I2CSlave() [2/2]

I2CSlave

(

const i2c_pinmap_t &

static_pinmap

)

Create an I2C Slave interface, connected to the specified pins.

Parameters

static_pinmap

reference to structure which holds static pinmap.

Member Function Documentation

frequency()

void frequency

(

int

hz

)

Set the frequency of the I2C interface.

Parameters

hz	The bus frequency in Hertz.

receive()

int receive

(

void

)

Check if this I2C Slave has been addressed.

Returns

A status indicating if the device has been addressed and how.

Return values

NoData	The slave has not been addressed.
ReadAddressed	The master has requested a read from this slave.
WriteAddressed	The master is writing to this slave.
WriteGeneral	The master is writing to all slave.

read() [1/2]

int read	(	char *	data,
		int	length
	)

Read bytes transmitted to this MCU from an I2C master.

Call this function only once receive() returns WriteAddressed or WriteGeneral.

Parameters

data	Pointer to the buffer to read data into.
length	Maximum number of bytes to read.

Returns

The number of bytes read

read() [2/2]

int read

(

void

)

Read a single byte from an I2C master.

Returns

The byte read.

write() [1/2]

int write	(	const char *	data,
		int	length
	)

Write to an I2C master which is addressing this slave device.

Call this function only once receive() returns ReadAddressed. This will send the given data bytes to the master and then send a NACK to end the read transaction.

Parameters

data	Pointer to the buffer containing the data to be sent.
length	Number of bytes to send.

Returns

Return values

0	If written all bytes successfully.
nonzero	On error or if the number of bytes written is less than requested.

write() [2/2]

int write

(

int

data

)

Write a single byte to an I2C master.

Parameters

data	Value to write.

Returns

Result of the operation.

Return values

0	If a NACK is received.
1	If an ACK is received.
2	On timeout.

address()

void address

(

int

address

)

Set the I2C slave address.

Parameters

address

The 8-bit address to set for the slave (least significant bit is ignored).

Note

If address is set to 0, the slave will only respond to the general call address.

stop()

void stop

(

void

)

Reset the I2C slave back into the known ready receiving state.