1I2CGET(8)                   System Manager's Manual                  I2CGET(8)
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NAME

6       i2cget - read from I2C/SMBus chip registers
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SYNOPSIS

10       i2cget   [-f]   [-y]   [-a]  i2cbus  chip-address  [data-address  [mode
11       [length]]]
12       i2cget -V
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DESCRIPTION

16       i2cget is a small helper program to read registers visible through  the
17       I2C bus (or SMBus).
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OPTIONS

21       -V     Display the version and exit.
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23       -f     Force  access  to  the device even if it is already busy. By de‐
24              fault, i2cget will refuse to access a device  which  is  already
25              under the control of a kernel driver. Using this flag is danger‐
26              ous, it can seriously confuse the kernel driver in question.  It
27              can also cause i2cget to return an invalid value. So use at your
28              own risk and only if you know what you're doing.
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30       -y     Disable interactive mode. By default, i2cget  will  wait  for  a
31              confirmation from the user before messing with the I2C bus. When
32              this flag is used, it will perform the operation directly.  This
33              is mainly meant to be used in scripts. Use with caution.
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35       -a     Allow  using  addresses between 0x00 - 0x07 and 0x78 - 0x7f. Not
36              recommended.
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38       There are two required options to i2cget. i2cbus indicates  the  number
39       or name of the I2C bus to be scanned.  This number should correspond to
40       one of the busses listed by i2cdetect -l.  chip-address  specifies  the
41       address  of  the  chip  on that bus, and is an integer between 0x08 and
42       0x77.
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44       data-address specifies the address on that chip to read from, and is an
45       integer  between 0x00 and 0xFF. If omitted, the currently active regis‐
46       ter will be read (if that makes sense for the considered chip).
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48       The mode parameter, if specified, is one of the letters b, w, c, or  i,
49       corresponding  to a read byte data, a read word data, a write byte/read
50       byte, an SMBus block read, or an I2C block  read  transaction,  respec‐
51       tively.  A  p can also be appended to the mode parameter to enable PEC,
52       except for I2C block transactions. If the mode  parameter  is  omitted,
53       i2cget defaults to a read byte data transaction, unless data-address is
54       also omitted, in which case the default (and only valid) transaction is
55       a single read byte.
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57       The  length  parameter, if applicable and specified, sets the length of
58       the block transaction. Valid values are between 1 and 32. Default value
59       is 32.
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WARNING

63       i2cget can be extremely dangerous if used improperly. I2C and SMBus are
64       designed in such a way that an SMBus read transaction can be seen as  a
65       write  transaction  by certain chips. This is particularly true if set‐
66       ting mode to cp (write byte/read byte with PEC). Be  extremely  careful
67       using this program.
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EXAMPLES

71       Get the value of 8-bit register 0x11 of the I2C device at 7-bit address
72       0x2d on bus 1 (i2c-1), after user confirmation:
73              # i2cget 1 0x2d 0x11
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75       Get the value of 16-bit register 0x00 of the I2C device  at  7-bit  ad‐
76       dress 0x48 on bus 1 (i2c-1), after user confirmation:
77              # i2cget 1 0x48 0x00 w
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79       Set  the  internal  pointer register of a 24C02 EEPROM at 7-bit address
80       0x50 on bus 9 (i2c-9) to 0x00, then read the first 2  bytes  from  that
81       EEPROM:
82              # i2cset -y 9 0x50 0x00 ; i2cget -y 9 0x50 ; i2cget -y 9 0x50
83       This  assumes  that  the  device  automatically increments its internal
84       pointer register on every read, and  supports  read  byte  transactions
85       (read  without specifying the register address, "Receive Byte" in SMBus
86       terminology.)  Most EEPROM devices behave that way. Note that  this  is
87       only  safe  as  long  as nobody else is accessing the I2C device at the
88       same time. A safer approach would be to use a "Read Word" SMBus  trans‐
89       action  instead,  or  an I2C Block Read transaction to read more than 2
90       bytes.
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92       Set the internal pointer register of a 24C32 EEPROM  at  7-bit  address
93       0x53  on bus 9 (i2c-9) to 0x0000, then read the first 2 bytes from that
94       EEPROM:
95              # i2cset -y 9 0x53 0x00 0x00 ; i2cget -y 9 0x53 ; i2cget -y 9 0x53
96       This again assumes that the device automatically increments its  inter‐
97       nal  pointer  register  on  every read, and supports read byte transac‐
98       tions. While the previous example was for a small  EEPROM  using  8-bit
99       internal  addressing,  this example is for a larger EEPROM using 16-bit
100       internal addressing. Beware that running this command on a small EEPROM
101       using  8-bit internal addressing would actually write 0x00 to the first
102       byte of that EEPROM. The safety concerns raised above still stand, how‐
103       ever in this case there is no SMBus equivalent, so this is the only way
104       to read data from a large EEPROM if your master isn't fully  I2C  capa‐
105       ble.  With  a  fully  I2C  capable master, you would use i2ctransfer to
106       achieve the same in a safe and faster way.
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108       Read the first 8 bytes of an EEPROM device at 7-bit address 0x50 on bus
109       4 (i2c-4):
110              # i2cget -y 4 0x50 0x00 i 8
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BUGS

114       To  report  bugs  or  send fixes, please write to the Linux I2C mailing
115       list <linux-i2c@vger.kernel.org> with Cc  to  the  current  maintainer:
116       Jean Delvare <jdelvare@suse.de>.
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SEE ALSO

120       i2cdetect(8), i2cdump(8), i2cset(8), i2ctransfer(8)
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AUTHOR

124       Jean Delvare
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126       This  manual  page  was strongly inspired from those written by David Z
127       Maze for i2cset.
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131                                   July 2021                         I2CGET(8)
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