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.TH I2CDUMP 8 "October 2017"
i2cdump \- examine I2C registers
.B i2cdump
.RB [ -f ]
.RB [ "-r first-last" ]
.RB [ -y ]
.I i2cbus
.I address
.RI [ "mode " [ "bank " [ bankreg ]]]
.B i2cdump
.B -V
i2cdump is a small helper program to examine registers
visible through the I2C bus.
.B -V
Display the version and exit.
.B -f
Force access to the device even if it is already busy. By default, i2cdump
will refuse to access a device which is already under the control of a
kernel driver. Using this flag is dangerous, it can seriously confuse the
kernel driver in question. It can also cause i2cdump to return invalid
results. So use at your own risk and only if you know what you're doing.
.B -r first-last
Limit the range of registers being accessed. This option is only available
with modes \fBb\fP, \fBw\fP, \fBc\fP and \fBW\fP. For mode \fBW\fP,
\fBfirst\fR must be even and \fBlast\fR must be odd.
.B -y
Disable interactive mode. By default, i2cdump 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
At least two options must be provided to i2cdump. \fIi2cbus\fR indicates the
number or name of the I2C bus to be scanned. This number should correspond to one
of the busses listed by \fIi2cdetect -l\fR. \fIaddress\fR indicates the
address to be scanned on that bus, and is an integer between 0x03 and 0x77.
The \fImode\fR parameter, if specified, is one of the letters \fBb\fP, \fBw\fP,
\fBs\fP, or \fBi\fP, corresponding to a read size of a single byte, a 16-bit
word, an SMBus block, an I2C block, respectively. The \fBc\fP mode is a
little different, it reads all bytes consecutively, and is useful for chips that
have an address auto-increment feature, such as EEPROMs. The \fBW\fP mode is
also special, it is similar to \fBw\fP except that a read command will only
be issued on even register addresses; this is again mainly useful for EEPROMs.
A \fBp\fP can also be appended to the \fImode\fR parameter (except for
\fBi\fP and \fBW\fP) to enable PEC. If the \fImode\fR parameter is omitted,
i2cdump defaults to byte access without PEC.
The \fIbank\fR and \fIbankreg\fR parameters are useful on the W83781D and
similar chips (at the time of writing, all Winbond and Asus chips).
\fIbank\fR is an integer between 0 and 7, and \fIbankreg\fR is an integer
between 0x00 and 0xFF (default value: 0x4E). The W83781D data sheet has more
information on bank selection.
i2cdump can be dangerous if used improperly. Most notably, the \fBc\fP mode
starts with WRITING a byte to the chip. On most chips it will be stored in the
address pointer register, which is OK, but some chips with a single register
or no (visible) register at all will most likely see this as a real WRITE,
resulting in possible misbehavior or corruption. Do not use i2cdump
on random addresses. Anyway, it is of little use unless you have good
knowledge of the chip you're working with and an idea of what you are looking
Dump the whole contents of I2C device at 7-bit address 0x50 on bus 9
(i2c-9), using the default read method (byte mode), after user confirmation:
# i2cdump 9 0x50
Immediately dump the whole contents of I2C device at 7-bit address 0x50 on
bus 9 (i2c-9), using I2C block read transactions (no user confirmation):
# i2cdump -y 9 0x50 i
If the device is an EEPROM, the output would typically be the same as output
of the previous example.
Dump registers 0x00 to 0x3f of the I2C device at 7-bit address 0x2d on
bus 1 (i2c-1), using the default read method (byte mode), after user
# i2cdump -r 0x00-0x3f 1 0x2d
Dump the registers of the SMBus device at address 0x69 on bus 0 (i2c-0),
using one SMBus block read transaction with error checking enabled, after
user confirmation:
# i2cdump 0 0x69 sp
i2cdetect(8), i2cget(8), i2cset(8), i2ctransfer(8), isadump(8)
Frodo Looijaard, Mark D. Studebaker and Jean Delvare
This manual page was originally written by David Z Maze <> for
the Debian GNU/Linux system.