linux/Documentation/misc-devices/max6875
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   1Kernel driver max6875
   2=====================
   3
   4Supported chips:
   5  * Maxim MAX6874, MAX6875
   6    Prefix: 'max6875'
   7    Addresses scanned: None (see below)
   8    Datasheet:
   9        http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
  10
  11Author: Ben Gardner <bgardner@wabtec.com>
  12
  13
  14Description
  15-----------
  16
  17The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
  18It provides timed outputs that can be used as a watchdog, if properly wired.
  19It also provides 512 bytes of user EEPROM.
  20
  21At reset, the MAX6875 reads the configuration EEPROM into its configuration
  22registers.  The chip then begins to operate according to the values in the
  23registers.
  24
  25The Maxim MAX6874 is a similar, mostly compatible device, with more intputs
  26and outputs:
  27             vin     gpi    vout
  28MAX6874        6       4       8
  29MAX6875        4       3       5
  30
  31See the datasheet for more information.
  32
  33
  34Sysfs entries
  35-------------
  36
  37eeprom        - 512 bytes of user-defined EEPROM space.
  38
  39
  40General Remarks
  41---------------
  42
  43Valid addresses for the MAX6875 are 0x50 and 0x52.
  44Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
  45The driver does not probe any address, so you explicitly instantiate the
  46devices.
  47
  48Example:
  49$ modprobe max6875
  50$ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
  51
  52The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
  53addresses.  For example, for address 0x50, it also reserves 0x51.
  54The even-address instance is called 'max6875', the odd one is 'dummy'.
  55
  56
  57Programming the chip using i2c-dev
  58----------------------------------
  59
  60Use the i2c-dev interface to access and program the chips.
  61Reads and writes are performed differently depending on the address range.
  62
  63The configuration registers are at addresses 0x00 - 0x45.
  64Use i2c_smbus_write_byte_data() to write a register and
  65i2c_smbus_read_byte_data() to read a register.
  66The command is the register number.
  67
  68Examples:
  69To write a 1 to register 0x45:
  70  i2c_smbus_write_byte_data(fd, 0x45, 1);
  71
  72To read register 0x45:
  73  value = i2c_smbus_read_byte_data(fd, 0x45);
  74
  75
  76The configuration EEPROM is at addresses 0x8000 - 0x8045.
  77The user EEPROM is at addresses 0x8100 - 0x82ff.
  78
  79Use i2c_smbus_write_word_data() to write a byte to EEPROM.
  80
  81The command is the upper byte of the address: 0x80, 0x81, or 0x82.
  82The data word is the lower part of the address or'd with data << 8.
  83  cmd = address >> 8;
  84  val = (address & 0xff) | (data << 8);
  85
  86Example:
  87To write 0x5a to address 0x8003:
  88  i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
  89
  90
  91Reading data from the EEPROM is a little more complicated.
  92Use i2c_smbus_write_byte_data() to set the read address and then
  93i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
  94
  95Example:
  96To read data starting at offset 0x8100, first set the address:
  97  i2c_smbus_write_byte_data(fd, 0x81, 0x00);
  98
  99And then read the data
 100  value = i2c_smbus_read_byte(fd);
 101
 102  or
 103
 104  count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
 105
 106The block read should read 16 bytes.
 1070x84 is the block read command.
 108
 109See the datasheet for more details.
 110
 111
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