I2CGET(8)I2CGET(8)NAMEi2cget - read from I2C/SMBus chip registers
SYNOPSISi2cget [-f] [-y] i2cbus chip-address [data-address [mode]]
i2cget-V
DESCRIPTIONi2cget is a small helper program to read registers visible through the
I2C bus (or SMBus).
OPTIONS-V Display the version and exit.
-f Force access to the device even if it is already busy. By
default, i2cget 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 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
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. Use with caution.
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 0x03 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 regis‐
ter will be read (if that makes sense for the considered chip).
The mode parameter, if specified, is one of the letters b, w or c, cor‐
responding to a read byte data, a read word data or a write byte/read
byte transaction, respectively. A p can also be appended to the mode
parameter to enable PEC. If the mode parameter is omitted, i2cget
defaults to a read byte data transaction, unless data-address is also
omitted, in which case the default (and only valid) transaction is a
single read byte.
WARNINGi2cget 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 set‐
ting 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 trans‐
action 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 inter‐
nal pointer register on every read, and supports read byte transac‐
tions. 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, how‐
ever 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 capa‐
ble. With a fully I2C capable master, you would use i2ctransfer to
achieve the same in a safe and faster way.
SEE ALSOi2cdetect(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.
October 2017 I2CGET(8)
