I2CSET(8) System Manager’s Manual I2CSET(8)
i2cset – set I2C registers
i2cset [-f] [-y] [-m mask] [-r] i2cbus chip-address data-address
[value] … [mode] i2cset -V
i2cset is a small helper program to set registers visible through the
-V Display the version and exit.
-f Force access to the device even if it is already busy. By
default, i2cset will refuse to access a device which is already
under the control of a kernel driver. Using this flag is danger‐
ous, it can seriously confuse the kernel driver in question. It
can also cause i2cset to silently write to the wrong register.
So use at your own risk and only if you know what you’re doing.
-y Disable interactive mode. By default, i2cset will wait for a
confirmation from the user before messing with the I2C bus. When
this flag is used, it will perform the operation directly. This
is mainly meant to be used in scripts.
The mask parameter, if specified, describes which bits of value
will be actually written to data-address. Bits set to 1 in the
mask are taken from value, while bits set to 0 will be read from
data-address and thus preserved by the operation. Please note
that this parameter assumes that the read and write operations
for the specified mode are symmetrical for the device you are
accessing. This may or may not be the case, as neither I2C nor
SMBus guarantees this.
-r Read back the value right after writing it, and compare the
result with the value written. This used to be the default
behavior. The same limitations apply as those of option -m.
There are three required options to i2cset. i2cbus indicates the number
or name of the I2C bus to be scanned. This number should correspond to
one of the busses listed by i2cdetect -l. chip-address specifies the
address of the chip on that bus, and is an integer between 0x03 and
0x77. data-address specifies the address on that chip to write to, and
is an integer between 0x00 and 0xFF.
The value parameter, if specified, is the value to write to that loca‐
tion on the chip. If this parameter is omitted, then a short write is
issued. For most chips, it simply sets an internal pointer to the tar‐
get location, but doesn’t actually write to that location. For a few
chips though, in particular simple ones with a single register, this
short write is an actual write. If the mode parameter is s or i, multi‐
ple values can be specified.
The mode parameter, if specified, is one of the letters b, w, s, or i,
corresponding to a write size of a single byte, a 16-bit word, a SMBus
block write, or an I2C block write, respectively. For SMBus and I2C
block writes, the write size is determined by the number of value
parameters. Except for I2C block writes, a p can also be appended to
the mode parameter to enable PEC. If the mode parameter is omitted,
i2cset defaults to byte mode without PEC. The value provided must be
within range for the specified data type (0x00-0xFF for byte and block
writes, 0x0000-0xFFFF for words). Another possible mode is c, which
doesn’t write any value (so-called short write). You usually don’t have
to specify this mode, as it is the default when no value is provided,
unless you also want to enable PEC.
i2cset can be extremely dangerous if used improperly. It can confuse
your I2C bus, cause data loss, or have more serious side effects. Writ‐
ing to a serial EEPROM on a memory DIMM (chip addresses between 0x50
and 0x57) may DESTROY your memory, leaving your system unbootable! Be
extremely careful using this program.
Frodo Looijaard, Mark D. Studebaker and Jean Delvare
This manual page was originally written by David Z Maze
November 2008 I2CSET(8)