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I2C(8)			  BSD System Manager's Manual			I2C(8)

     i2c -- test I2C bus and slave devices

     i2c -a address [-f	device]	[-d r|w] [-w 0|8|16] [-o offset] [-c count]
	 [-m ss|rs|no] [-b] [-v]
     i2c -s [-f	device]	[-n skip_addr] [-v]
     i2c -r [-f	device]	[-v]

     The i2c utility can be used to perform raw	data transfers (read or	write)
     with devices on the I2C bus. It can also scan the bus for available de-
     vices and reset the I2C controller.

     The options are as	follows:

     -a	address	   7-bit address on the	I2C device to operate on (hex).

     -b		   binary mode - when performing a read	operation, the data
		   read	from the device	is output in binary format on stdout;
		   when	doing a	write, the binary data to be written to	the
		   device is read from stdin.

     -c	count	   number of bytes to transfer (dec).

     -d	r|w	   transfer direction: r - read, w - write.

     -f	device	   I2C bus to use (default is /dev/iic0).

     -m	ss|rs|no   addressing mode, i.e., I2C bus operations performed after
		   the offset for the transfer has been	written	to the device
		   and before the actual read/write operation. rs - repeated
		   start; ss - stop start; no -	none.

     -n	skip_addr  skip	address	- address(es) to be skipped during bus scan.
		   There are two ways to specify addresses to ignore: by range
		   'a..b' or using selected addresses 'a:b:c'. This option is
		   available only when "-s" is used.

     -o	offset	   offset within the device for	data transfer (hex).

     -r		   reset the controller.

     -s		   scan	the bus	for devices.

     -v		   be verbose.

     -w	0|8|16	   device addressing width (in bits).

     Great care	must be	taken when manipulating	slave I2C devices with the i2c
     utility. Often times important configuration data for the system is kept
     in	non-volatile but write enabled memories	located	on the I2C bus,	for
     example Ethernet hardware addresses, RAM module parameters	(SPD), proces-
     sor reset configuration word etc.

     It	is very	easy to	render the whole system	unusable when such configura-
     tion data is deleted or altered, so use the "-d w"	(write)	command	only
     if	you know exactly what you are doing.

     Also avoid	ungraceful interrupting	of an ongoing transaction on the I2C
     bus, as it	can lead to potentially	dangerous effects. Consider the	fol-
     lowing scenario: when the host CPU	is reset (for whatever reason) in the
     middle of a started I2C transaction, the I2C slave	device could be	left
     in	write mode waiting for data or offset to arrive. When the CPU reini-
     tializes itself and talks to this I2C slave device	again, the commands
     and other control info it sends are treated by the	slave device as	data
     or	offset it was waiting for, and there's great potential for corruption
     if	such a write is	performed.

     +o	 Scan the default bus (/dev/iic0) for devices:

	 i2c -s

     +o	 Scan the default bus (/dev/iic0) for devices and skip addresses 0x56
	 and 0x45.

	 i2c -s	-n 0x56:0x45

     +o	 Scan the default bus (/dev/iic0) for devices and skip address range
	 0x34 to 0x56.

	 i2c -s	-n 0x34..0x56

     +o	 Read 8	bytes of data from device at address 0x56 (e.g., an EEPROM):

	 i2c -a	0x56 -d	r -c 8

     +o	 Write 16 bytes	of data	from file data.bin to device 0x56 at offset

	 i2c -a	0x56 -d	w -c 16	-o 0x10	-b < data.bin

     +o	 Copy 4	bytes between two EEPROMs (0x56	on /dev/iic1 to	0x57 on

	 i2c -a	0x56 -f	/dev/iic1 -d r -c 0x4 -b | i2c -a 0x57 -f /dev/iic0 -d
	 w -c 4	-b

     +o	 Reset the controller:

	 i2c -f	/dev/iic1 -r

     iic(4), iicbus(4)

     The i2c utility appeared in FreeBSD 8.0.

     The i2c utility and this manual page were written by Bartlomiej Sieka
     <>	and Michal Hajduk <>.

BSD			       January 23, 2009				   BSD


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