I2C access

Detailed Description

These functions let you use I2C (The Broadcom Serial Control bus with the Philips I2C bus/interface version 2.1 January 2000.) to interface with an external I2C device.

Functions
int	bcm2835_i2c_begin (void)
void	bcm2835_i2c_end (void)
void	bcm2835_i2c_setSlaveAddress (uint8_t addr)
void	bcm2835_i2c_setClockDivider (uint16_t divider)
void	bcm2835_i2c_set_baudrate (uint32_t baudrate)
uint8_t	bcm2835_i2c_write (const char *buf, uint32_t len)
uint8_t	bcm2835_i2c_read (char *buf, uint32_t len)
uint8_t	bcm2835_i2c_read_register_rs (char *regaddr, char *buf, uint32_t len)
uint8_t	bcm2835_i2c_write_read_rs (char *cmds, uint32_t cmds_len, char *buf, uint32_t buf_len)

Function Documentation

bcm2835_i2c_begin()

int bcm2835_i2c_begin

(

void

)

Start I2C operations. Forces RPi I2C pins P1-03 (SDA) and P1-05 (SCL) to alternate function ALT0, which enables those pins for I2C interface. You should call bcm2835_i2c_end() when all I2C functions are complete to return the pins to their default functions

Returns

1 if successful, 0 otherwise (perhaps because you are not running as root)

See also

bcm2835_i2c_end()

bcm2835_i2c_end()

void bcm2835_i2c_end

(

void

)

End I2C operations. I2C pins P1-03 (SDA) and P1-05 (SCL) are returned to their default INPUT behaviour.

bcm2835_i2c_read()

uint8_t bcm2835_i2c_read	(	char *	buf,
		uint32_t	len
	)

Transfers any number of bytes from the currently selected I2C slave. (as previously set by

See also

bcm2835_i2c_setSlaveAddress)

Parameters

[in]	buf	Buffer of bytes to receive.
[in]	len	Number of bytes in the buf buffer, and the number of bytes to received.

Returns

reason see bcm2835I2CReasonCodes

bcm2835_i2c_read_register_rs()

uint8_t bcm2835_i2c_read_register_rs	(	char *	regaddr,
		char *	buf,
		uint32_t	len
	)

Allows reading from I2C slaves that require a repeated start (without any prior stop) to read after the required slave register has been set. For example, the popular MPL3115A2 pressure and temperature sensor. Note that your device must support or require this mode. If your device does not require this mode then the standard combined:

See also

bcm2835_i2c_write

bcm2835_i2c_read are a better choice. Will read from the slave previously set by

bcm2835_i2c_setSlaveAddress

Parameters

[in]	regaddr	Buffer containing the slave register you wish to read from.
[in]	buf	Buffer of bytes to receive.
[in]	len	Number of bytes in the buf buffer, and the number of bytes to received.

Returns

reason see bcm2835I2CReasonCodes

bcm2835_i2c_set_baudrate()

void bcm2835_i2c_set_baudrate

(

uint32_t

baudrate

)

Sets the I2C clock divider by converting the baudrate parameter to the equivalent I2C clock divider. ( see

See also

bcm2835_i2c_setClockDivider) For the I2C standard 100khz you would set baudrate to 100000 The use of baudrate corresponds to its use in the I2C kernel device driver. (Of course, bcm2835 has nothing to do with the kernel driver)

bcm2835_i2c_setClockDivider()

void bcm2835_i2c_setClockDivider

(

uint16_t

divider

)

Sets the I2C clock divider and therefore the I2C clock speed.

Parameters

[in]

divider

The desired I2C clock divider, one of BCM2835_I2C_CLOCK_DIVIDER_*, see bcm2835I2CClockDivider

bcm2835_i2c_setSlaveAddress()

void bcm2835_i2c_setSlaveAddress

(

uint8_t

addr

)

Sets the I2C slave address.

Parameters

[in]

addr

The I2C slave address.

bcm2835_i2c_write()

uint8_t bcm2835_i2c_write	(	const char *	buf,
		uint32_t	len
	)

Transfers any number of bytes to the currently selected I2C slave. (as previously set by

See also

bcm2835_i2c_setSlaveAddress)

Parameters

[in]	buf	Buffer of bytes to send.
[in]	len	Number of bytes in the buf buffer, and the number of bytes to send.

Returns

reason see bcm2835I2CReasonCodes

bcm2835_i2c_write_read_rs()

uint8_t bcm2835_i2c_write_read_rs	(	char *	cmds,
		uint32_t	cmds_len,
		char *	buf,
		uint32_t	buf_len
	)

Allows sending an arbitrary number of bytes to I2C slaves before issuing a repeated start (with no prior stop) and reading a response. Necessary for devices that require such behavior, such as the MLX90620. Will write to and read from the slave previously set by

See also

bcm2835_i2c_setSlaveAddress

Parameters

[in]	cmds	Buffer containing the bytes to send before the repeated start condition.
[in]	cmds_len	Number of bytes to send from cmds buffer
[in]	buf	Buffer of bytes to receive.
[in]	buf_len	Number of bytes to receive in the buf buffer.

Returns

reason see bcm2835I2CReasonCodes