I2CGET(8) System Manager's Manual I2CGET(8)
NAME
i2cget - read from I2C/SMBus chip registers
SYNOPSIS
i2cget [-f] [-y] [-a] i2cbus chip-address [data-address [mode [length]]]
i2cget -V
i2cget -h
DESCRIPTION
i2cget is a small helper program to read registers visible through the
I2C bus (or SMBus).
OPTIONS
-V Display the version and exit.
-h Display the help and exit.
-f Force access to the device even if it is already busy. By de-
fault, i2cget will refuse to access a device which is already un-
der the control of a kernel driver. Using this flag is dangerous,
it can seriously confuse the kernel driver in question. It can
also cause i2cget to return an invalid value. So use at your own
risk and only if you know what you're doing.
-y Disable interactive mode. By default, i2cget will wait for a con-
firmation 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. Use with caution.
-a Allow using addresses between 0x00 - 0x07 and 0x78 - 0x7f. Not
recommended.
There are two required options to i2cget. 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 0x08 and 0x77.
data-address specifies the address on that chip to read from, and is an
integer between 0x00 and 0xFF. If omitted, the currently active register
will be read (if that makes sense for the considered chip).
The mode parameter, if specified, is one of the letters b, w, c, s, or
i, corresponding to a read byte data, a read word data, a write
byte/read byte, an SMBus block read, or an I2C block read transaction,
respectively. A p can also be appended to the mode parameter to enable
PEC, except for I2C block transactions. If the mode parameter is omit-
ted, i2cget defaults to a read byte data transaction, unless data-ad-
dress is also omitted, in which case the default (and only valid) trans-
action is a single read byte.
The length parameter, if applicable and specified, sets the length of
the block transaction. Valid values are between 1 and 32. Default value
is 32.
WARNING
i2cget can be extremely dangerous if used improperly. I2C and SMBus are
designed in such a way that an SMBus read transaction can be seen as a
write transaction by certain chips. This is particularly true if setting
mode to cp (write byte/read byte with PEC). Be extremely careful using
this program.
EXAMPLES
Get the value of 8-bit register 0x11 of the I2C device at 7-bit address
0x2d on bus 1 (i2c-1), after user confirmation:
# i2cget 1 0x2d 0x11
Get the value of 16-bit register 0x00 of the I2C device at 7-bit address
0x48 on bus 1 (i2c-1), after user confirmation:
# i2cget 1 0x48 0x00 w
Set the internal pointer register of a 24C02 EEPROM at 7-bit address
0x50 on bus 9 (i2c-9) to 0x00, then read the first 2 bytes from that
EEPROM:
# i2cset -y 9 0x50 0x00 ; i2cget -y 9 0x50 ; i2cget -y 9 0x50
This assumes that the device automatically increments its internal
pointer register on every read, and supports read byte transactions
(read without specifying the register address, "Receive Byte" in SMBus
terminology.) Most EEPROM devices behave that way. Note that this is
only safe as long as nobody else is accessing the I2C device at the same
time. A safer approach would be to use a "Read Word" SMBus transaction
instead, or an I2C Block Read transaction to read more than 2 bytes.
Set the internal pointer register of a 24C32 EEPROM at 7-bit address
0x53 on bus 9 (i2c-9) to 0x0000, then read the first 2 bytes from that
EEPROM:
# i2cset -y 9 0x53 0x00 0x00 ; i2cget -y 9 0x53 ; i2cget -y 9 0x53
This again assumes that the device automatically increments its internal
pointer register on every read, and supports read byte transactions.
While the previous example was for a small EEPROM using 8-bit internal
addressing, this example is for a larger EEPROM using 16-bit internal
addressing. Beware that running this command on a small EEPROM using
8-bit internal addressing would actually write 0x00 to the first byte of
that EEPROM. The safety concerns raised above still stand, however in
this case there is no SMBus equivalent, so this is the only way to read
data from a large EEPROM if your master isn't fully I2C capable. With a
fully I2C capable master, you would use i2ctransfer to achieve the same
in a safe and faster way.
Read the first 8 bytes of an EEPROM device at 7-bit address 0x50 on bus
4 (i2c-4):
# i2cget -y 4 0x50 0x00 i 8
BUGS
To report bugs or send fixes, please write to the Linux I2C mailing list
<linux-i2c@vger.kernel.org> with Cc to the current maintainer: Jean Del-
vare <jdelvare@suse.de>.
SEE ALSO
i2cdetect(8), i2cdump(8), i2cset(8), i2ctransfer(8)
AUTHOR
Jean Delvare
This manual page was strongly inspired from those written by David Z
Maze for i2cset.
May 2022 I2CGET(8)
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