NAME

       i2cget - read from I2C/SMBus chip registers

SYNOPSIS

       i2cget [-f] [-y] [-a] i2cbus chip-address [data-address [mode [length]]]
       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.

       -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, 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 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.

       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 Delvare <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.

                                                    July 2021                                          I2CGET(8)