max6875.rst (3233B)
1===================== 2Kernel driver max6875 3===================== 4 5Supported 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 15Author: Ben Gardner <bgardner@wabtec.com> 16 17 18Description 19----------- 20 21The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. 22It provides timed outputs that can be used as a watchdog, if properly wired. 23It also provides 512 bytes of user EEPROM. 24 25At reset, the MAX6875 reads the configuration EEPROM into its configuration 26registers. The chip then begins to operate according to the values in the 27registers. 28 29The Maxim MAX6874 is a similar, mostly compatible device, with more inputs 30and outputs: 31 32=========== === === ==== 33- vin gpi vout 34=========== === === ==== 35MAX6874 6 4 8 36MAX6875 4 3 5 37=========== === === ==== 38 39See the datasheet for more information. 40 41 42Sysfs entries 43------------- 44 45eeprom - 512 bytes of user-defined EEPROM space. 46 47 48General Remarks 49--------------- 50 51Valid addresses for the MAX6875 are 0x50 and 0x52. 52 53Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. 54 55The driver does not probe any address, so you explicitly instantiate the 56devices. 57 58Example:: 59 60 $ modprobe max6875 61 $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device 62 63The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple 64addresses. For example, for address 0x50, it also reserves 0x51. 65The even-address instance is called 'max6875', the odd one is 'dummy'. 66 67 68Programming the chip using i2c-dev 69---------------------------------- 70 71Use the i2c-dev interface to access and program the chips. 72 73Reads and writes are performed differently depending on the address range. 74 75The configuration registers are at addresses 0x00 - 0x45. 76 77Use i2c_smbus_write_byte_data() to write a register and 78i2c_smbus_read_byte_data() to read a register. 79 80The command is the register number. 81 82Examples: 83 84To write a 1 to register 0x45:: 85 86 i2c_smbus_write_byte_data(fd, 0x45, 1); 87 88To read register 0x45:: 89 90 value = i2c_smbus_read_byte_data(fd, 0x45); 91 92 93The configuration EEPROM is at addresses 0x8000 - 0x8045. 94 95The user EEPROM is at addresses 0x8100 - 0x82ff. 96 97Use i2c_smbus_write_word_data() to write a byte to EEPROM. 98 99The command is the upper byte of the address: 0x80, 0x81, or 0x82. 100The 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 105Example: 106 107To write 0x5a to address 0x8003:: 108 109 i2c_smbus_write_word_data(fd, 0x80, 0x5a03); 110 111 112Reading data from the EEPROM is a little more complicated. 113 114Use i2c_smbus_write_byte_data() to set the read address and then 115i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data. 116 117Example: 118 119To read data starting at offset 0x8100, first set the address:: 120 121 i2c_smbus_write_byte_data(fd, 0x81, 0x00); 122 123And then read the data:: 124 125 value = i2c_smbus_read_byte(fd); 126 127or:: 128 129 count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer); 130 131The block read should read 16 bytes. 132 1330x84 is the block read command. 134 135See the datasheet for more details. 136