1 ===================== 2 Kernel driver max6875 3 ===================== 4 5 Supported chips: 6 7 * Maxim MAX6874, MAX6875 8 9 Prefix: 'max6875' 10 11 Addresses scanned: None (see below) 12 13 Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf 14 15 Author: Ben Gardner <bgardner@wabtec.com> 16 17 18 Description 19 ----------- 20 21 The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. 22 It provides timed outputs that can be used as a watchdog, if properly wired. 23 It also provides 512 bytes of user EEPROM. 24 25 At reset, the MAX6875 reads the configuration EEPROM into its configuration 26 registers. The chip then begins to operate according to the values in the 27 registers. 28 29 The Maxim MAX6874 is a similar, mostly compatible device, with more inputs 30 and outputs: 31 32 =========== === === ==== 33 - vin gpi vout 34 =========== === === ==== 35 MAX6874 6 4 8 36 MAX6875 4 3 5 37 =========== === === ==== 38 39 See the datasheet for more information. 40 41 42 Sysfs entries 43 ------------- 44 45 eeprom - 512 bytes of user-defined EEPROM space. 46 47 48 General Remarks 49 --------------- 50 51 Valid addresses for the MAX6875 are 0x50 and 0x52. 52 53 Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. 54 55 The driver does not probe any address, so you explicitly instantiate the 56 devices. 57 58 Example:: 59 60 $ modprobe max6875 61 $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device 62 63 The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple 64 addresses. For example, for address 0x50, it also reserves 0x51. 65 The even-address instance is called 'max6875', the odd one is 'dummy'. 66 67 68 Programming the chip using i2c-dev 69 ---------------------------------- 70 71 Use the i2c-dev interface to access and program the chips. 72 73 Reads and writes are performed differently depending on the address range. 74 75 The configuration registers are at addresses 0x00 - 0x45. 76 77 Use i2c_smbus_write_byte_data() to write a register and 78 i2c_smbus_read_byte_data() to read a register. 79 80 The command is the register number. 81 82 Examples: 83 84 To write a 1 to register 0x45:: 85 86 i2c_smbus_write_byte_data(fd, 0x45, 1); 87 88 To read register 0x45:: 89 90 value = i2c_smbus_read_byte_data(fd, 0x45); 91 92 93 The configuration EEPROM is at addresses 0x8000 - 0x8045. 94 95 The user EEPROM is at addresses 0x8100 - 0x82ff. 96 97 Use i2c_smbus_write_word_data() to write a byte to EEPROM. 98 99 The command is the upper byte of the address: 0x80, 0x81, or 0x82. 100 The data word is the lower part of the address or'd with data << 8:: 101 102 cmd = address >> 8; 103 val = (address & 0xff) | (data << 8); 104 105 Example: 106 107 To write 0x5a to address 0x8003:: 108 109 i2c_smbus_write_word_data(fd, 0x80, 0x5a03); 110 111 112 Reading data from the EEPROM is a little more complicated. 113 114 Use i2c_smbus_write_byte_data() to set the read address and then 115 i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data. 116 117 Example: 118 119 To read data starting at offset 0x8100, first set the address:: 120 121 i2c_smbus_write_byte_data(fd, 0x81, 0x00); 122 123 And then read the data:: 124 125 value = i2c_smbus_read_byte(fd); 126 127 or:: 128 129 count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer); 130 131 The block read should read 16 bytes. 132 133 0x84 is the block read command. 134 135 See the datasheet for more details. 136
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