1 ===================== 1 =====================
2 Kernel driver max6875 2 Kernel driver max6875
3 ===================== 3 =====================
4 4
5 Supported chips: 5 Supported chips:
6 6
7 * Maxim MAX6874, MAX6875 7 * Maxim MAX6874, MAX6875
8 8
9 Prefix: 'max6875' 9 Prefix: 'max6875'
10 10
11 Addresses scanned: None (see below) 11 Addresses scanned: None (see below)
12 12
13 Datasheet: http://pdfserv.maxim-ic.com/en/ 13 Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
14 14
15 Author: Ben Gardner <bgardner@wabtec.com> 15 Author: Ben Gardner <bgardner@wabtec.com>
16 16
17 17
18 Description 18 Description
19 ----------- 19 -----------
20 20
21 The Maxim MAX6875 is an EEPROM-programmable po 21 The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
22 It provides timed outputs that can be used as 22 It provides timed outputs that can be used as a watchdog, if properly wired.
23 It also provides 512 bytes of user EEPROM. 23 It also provides 512 bytes of user EEPROM.
24 24
25 At reset, the MAX6875 reads the configuration 25 At reset, the MAX6875 reads the configuration EEPROM into its configuration
26 registers. The chip then begins to operate ac 26 registers. The chip then begins to operate according to the values in the
27 registers. 27 registers.
28 28
29 The Maxim MAX6874 is a similar, mostly compati 29 The Maxim MAX6874 is a similar, mostly compatible device, with more inputs
30 and outputs: 30 and outputs:
31 31
32 =========== === === ==== 32 =========== === === ====
33 - vin gpi vout 33 - vin gpi vout
34 =========== === === ==== 34 =========== === === ====
35 MAX6874 6 4 8 35 MAX6874 6 4 8
36 MAX6875 4 3 5 36 MAX6875 4 3 5
37 =========== === === ==== 37 =========== === === ====
38 38
39 See the datasheet for more information. 39 See the datasheet for more information.
40 40
41 41
42 Sysfs entries 42 Sysfs entries
43 ------------- 43 -------------
44 44
45 eeprom - 512 bytes of user-defined EEPR 45 eeprom - 512 bytes of user-defined EEPROM space.
46 46
47 47
48 General Remarks 48 General Remarks
49 --------------- 49 ---------------
50 50
51 Valid addresses for the MAX6875 are 0x50 and 0 51 Valid addresses for the MAX6875 are 0x50 and 0x52.
52 52
53 Valid addresses for the MAX6874 are 0x50, 0x52 53 Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
54 54
55 The driver does not probe any address, so you 55 The driver does not probe any address, so you explicitly instantiate the
56 devices. 56 devices.
57 57
58 Example:: 58 Example::
59 59
60 $ modprobe max6875 60 $ modprobe max6875
61 $ echo max6875 0x50 > /sys/bus/i2c/devices/i 61 $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
62 62
63 The MAX6874/MAX6875 ignores address bit 0, so 63 The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
64 addresses. For example, for address 0x50, it 64 addresses. For example, for address 0x50, it also reserves 0x51.
65 The even-address instance is called 'max6875', 65 The even-address instance is called 'max6875', the odd one is 'dummy'.
66 66
67 67
68 Programming the chip using i2c-dev 68 Programming the chip using i2c-dev
69 ---------------------------------- 69 ----------------------------------
70 70
71 Use the i2c-dev interface to access and progra 71 Use the i2c-dev interface to access and program the chips.
72 72
73 Reads and writes are performed differently dep 73 Reads and writes are performed differently depending on the address range.
74 74
75 The configuration registers are at addresses 0 75 The configuration registers are at addresses 0x00 - 0x45.
76 76
77 Use i2c_smbus_write_byte_data() to write a reg 77 Use i2c_smbus_write_byte_data() to write a register and
78 i2c_smbus_read_byte_data() to read a register. 78 i2c_smbus_read_byte_data() to read a register.
79 79
80 The command is the register number. 80 The command is the register number.
81 81
82 Examples: 82 Examples:
83 83
84 To write a 1 to register 0x45:: 84 To write a 1 to register 0x45::
85 85
86 i2c_smbus_write_byte_data(fd, 0x45, 1); 86 i2c_smbus_write_byte_data(fd, 0x45, 1);
87 87
88 To read register 0x45:: 88 To read register 0x45::
89 89
90 value = i2c_smbus_read_byte_data(fd, 0x45); 90 value = i2c_smbus_read_byte_data(fd, 0x45);
91 91
92 92
93 The configuration EEPROM is at addresses 0x800 93 The configuration EEPROM is at addresses 0x8000 - 0x8045.
94 94
95 The user EEPROM is at addresses 0x8100 - 0x82f 95 The user EEPROM is at addresses 0x8100 - 0x82ff.
96 96
97 Use i2c_smbus_write_word_data() to write a byt 97 Use i2c_smbus_write_word_data() to write a byte to EEPROM.
98 98
99 The command is the upper byte of the address: 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 100 The data word is the lower part of the address or'd with data << 8::
101 101
102 cmd = address >> 8; 102 cmd = address >> 8;
103 val = (address & 0xff) | (data << 8); 103 val = (address & 0xff) | (data << 8);
104 104
105 Example: 105 Example:
106 106
107 To write 0x5a to address 0x8003:: 107 To write 0x5a to address 0x8003::
108 108
109 i2c_smbus_write_word_data(fd, 0x80, 0x5a03); 109 i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
110 110
111 111
112 Reading data from the EEPROM is a little more 112 Reading data from the EEPROM is a little more complicated.
113 113
114 Use i2c_smbus_write_byte_data() to set the rea 114 Use i2c_smbus_write_byte_data() to set the read address and then
115 i2c_smbus_read_byte() or i2c_smbus_read_i2c_bl 115 i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
116 116
117 Example: 117 Example:
118 118
119 To read data starting at offset 0x8100, first 119 To read data starting at offset 0x8100, first set the address::
120 120
121 i2c_smbus_write_byte_data(fd, 0x81, 0x00); 121 i2c_smbus_write_byte_data(fd, 0x81, 0x00);
122 122
123 And then read the data:: 123 And then read the data::
124 124
125 value = i2c_smbus_read_byte(fd); 125 value = i2c_smbus_read_byte(fd);
126 126
127 or:: 127 or::
128 128
129 count = i2c_smbus_read_i2c_block_data(fd, 0x 129 count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
130 130
131 The block read should read 16 bytes. 131 The block read should read 16 bytes.
132 132
133 0x84 is the block read command. 133 0x84 is the block read command.
134 134
135 See the datasheet for more details. 135 See the datasheet for more details.
136 136
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