NAME

       i2cget - read from I2C/SMBus chip registers

SYNOPSIS

       i2cget [-f] [-y] i2cbus chip-address [data-address [mode]]
       i2cget -V

DESCRIPTION

       i2cget 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  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 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 register 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, corresponding 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.

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.

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.

                                           October 2017                                 I2CGET(8)