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
137