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] i2cbus chip-address [data-address [mode]]
11       i2cget -V
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DESCRIPTION

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

20       -V     Display the version and exit.
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22       -f     Force access to the device  even  if  it  is  already  busy.  By
23              default,  i2cget will refuse to access a device which is already
24              under the control of a kernel driver. Using this flag is danger‐
25              ous,  it can seriously confuse the kernel driver in question. It
26              can also cause i2cget to return an invalid value. So use at your
27              own risk and only if you know what you're doing.
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29       -y     Disable  interactive  mode.  By  default, i2cget will wait for a
30              confirmation from the user before messing with the I2C bus. When
31              this  flag is used, it will perform the operation directly. This
32              is mainly meant to be used in scripts. Use with caution.
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34       There are two required options to i2cget. i2cbus indicates  the  number
35       or name of the I2C bus to be scanned.  This number should correspond to
36       one of the busses listed by i2cdetect -l.  chip-address  specifies  the
37       address  of  the  chip  on that bus, and is an integer between 0x03 and
38       0x77.
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40       data-address specifies the address on that chip to read from, and is an
41       integer  between 0x00 and 0xFF. If omitted, the currently active regis‐
42       ter will be read (if that makes sense for the considered chip).
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44       The mode parameter, if specified, is one of the letters b, w or c, cor‐
45       responding  to  a read byte data, a read word data or a write byte/read
46       byte transaction, respectively. A p can also be appended  to  the  mode
47       parameter  to  enable  PEC.  If  the  mode parameter is omitted, i2cget
48       defaults to a read byte data transaction, unless data-address  is  also
49       omitted,  in  which  case the default (and only valid) transaction is a
50       single read byte.
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WARNING

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

62       Get the value of 8-bit register 0x11 of the I2C device at 7-bit address
63       0x2d on bus 1 (i2c-1), after user confirmation:
64              # i2cget 1 0x2d 0x11
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66       Get  the  value  of  16-bit  register  0x00  of the I2C device at 7-bit
67       address 0x48 on bus 1 (i2c-1), after user confirmation:
68              # i2cget 1 0x48 0x00 w
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70       Set the internal pointer register of a 24C02 EEPROM  at  7-bit  address
71       0x50  on  bus  9 (i2c-9) to 0x00, then read the first 2 bytes from that
72       EEPROM:
73              # i2cset -y 9 0x50 0x00 ; i2cget -y 9 0x50 ; i2cget -y 9 0x50
74       This assumes that the  device  automatically  increments  its  internal
75       pointer  register  on  every  read, and supports read byte transactions
76       (read without specifying the register address, "Receive Byte" in  SMBus
77       terminology.)   Most  EEPROM devices behave that way. Note that this is
78       only safe as long as nobody else is accessing the  I2C  device  at  the
79       same  time. A safer approach would be to use a "Read Word" SMBus trans‐
80       action instead, or an I2C Block Read transaction to read  more  than  2
81       bytes.
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83       Set  the  internal  pointer register of a 24C32 EEPROM at 7-bit address
84       0x53 on bus 9 (i2c-9) to 0x0000, then read the first 2 bytes from  that
85       EEPROM:
86              # i2cset -y 9 0x53 0x00 0x00 ; i2cget -y 9 0x53 ; i2cget -y 9 0x53
87       This  again assumes that the device automatically increments its inter‐
88       nal pointer register on every read, and  supports  read  byte  transac‐
89       tions.  While  the  previous example was for a small EEPROM using 8-bit
90       internal addressing, this example is for a larger EEPROM  using  16-bit
91       internal addressing. Beware that running this command on a small EEPROM
92       using 8-bit internal addressing would actually write 0x00 to the  first
93       byte of that EEPROM. The safety concerns raised above still stand, how‐
94       ever in this case there is no SMBus equivalent, so this is the only way
95       to  read  data from a large EEPROM if your master isn't fully I2C capa‐
96       ble. With a fully I2C capable master,  you  would  use  i2ctransfer  to
97       achieve the same in a safe and faster way.
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SEE ALSO

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

105       Jean Delvare
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107       This  manual  page  was strongly inspired from those written by David Z
108       Maze for i2cset.
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112                                 October 2017                        I2CGET(8)
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