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1 | Kernel driver max6875 |
2 | ===================== | |
3 | ||
4 | Supported chips: | |
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5 | * Maxim MAX6874, MAX6875 |
6 | Prefix: 'max6875' | |
93ffa435 | 7 | Addresses scanned: None (see below) |
089bd866 | 8 | Datasheet: |
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9 | http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf |
10 | ||
11 | Author: Ben Gardner <bgardner@wabtec.com> | |
12 | ||
13 | ||
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14 | Description |
15 | ----------- | |
16 | ||
089bd866 | 17 | The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. |
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18 | It provides timed outputs that can be used as a watchdog, if properly wired. |
19 | It also provides 512 bytes of user EEPROM. | |
20 | ||
089bd866 | 21 | At reset, the MAX6875 reads the configuration EEPROM into its configuration |
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22 | registers. The chip then begins to operate according to the values in the |
23 | registers. | |
24 | ||
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25 | The Maxim MAX6874 is a similar, mostly compatible device, with more intputs |
26 | and outputs: | |
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27 | vin gpi vout |
28 | MAX6874 6 4 8 | |
29 | MAX6875 4 3 5 | |
30 | ||
93ffa435 | 31 | See the datasheet for more information. |
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32 | |
33 | ||
34 | Sysfs entries | |
35 | ------------- | |
36 | ||
93ffa435 | 37 | eeprom - 512 bytes of user-defined EEPROM space. |
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38 | |
39 | ||
40 | General Remarks | |
41 | --------------- | |
42 | ||
93ffa435 | 43 | Valid addresses for the MAX6875 are 0x50 and 0x52. |
44 | Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. | |
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45 | The driver does not probe any address, so you explicitly instantiate the |
46 | devices. | |
93ffa435 | 47 | |
48 | Example: | |
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49 | $ modprobe max6875 |
50 | $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device | |
93ffa435 | 51 | |
52 | The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple | |
53 | addresses. For example, for address 0x50, it also reserves 0x51. | |
bd8d421f | 54 | The even-address instance is called 'max6875', the odd one is 'dummy'. |
93ffa435 | 55 | |
56 | ||
57 | Programming the chip using i2c-dev | |
58 | ---------------------------------- | |
59 | ||
60 | Use the i2c-dev interface to access and program the chips. | |
0283fe6c | 61 | Reads and writes are performed differently depending on the address range. |
93ffa435 | 62 | |
63 | The configuration registers are at addresses 0x00 - 0x45. | |
64 | Use i2c_smbus_write_byte_data() to write a register and | |
65 | i2c_smbus_read_byte_data() to read a register. | |
66 | The command is the register number. | |
67 | ||
68 | Examples: | |
69 | To write a 1 to register 0x45: | |
70 | i2c_smbus_write_byte_data(fd, 0x45, 1); | |
71 | ||
72 | To read register 0x45: | |
73 | value = i2c_smbus_read_byte_data(fd, 0x45); | |
74 | ||
75 | ||
76 | The configuration EEPROM is at addresses 0x8000 - 0x8045. | |
77 | The user EEPROM is at addresses 0x8100 - 0x82ff. | |
78 | ||
79 | Use i2c_smbus_write_word_data() to write a byte to EEPROM. | |
80 | ||
81 | The command is the upper byte of the address: 0x80, 0x81, or 0x82. | |
82 | The 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 | ||
86 | Example: | |
87 | To write 0x5a to address 0x8003: | |
88 | i2c_smbus_write_word_data(fd, 0x80, 0x5a03); | |
89 | ||
90 | ||
91 | Reading data from the EEPROM is a little more complicated. | |
92 | Use i2c_smbus_write_byte_data() to set the read address and then | |
93 | i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data. | |
94 | ||
95 | Example: | |
96 | To read data starting at offset 0x8100, first set the address: | |
97 | i2c_smbus_write_byte_data(fd, 0x81, 0x00); | |
98 | ||
99 | And then read the data | |
100 | value = i2c_smbus_read_byte(fd); | |
101 | ||
102 | or | |
103 | ||
4b2643d7 | 104 | count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer); |
93ffa435 | 105 | |
106 | The block read should read 16 bytes. | |
107 | 0x84 is the block read command. | |
108 | ||
109 | See the datasheet for more details. | |
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