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2 | Kernel driver max6875 |
3 | ===================== | |
4 | ||
5 | Supported chips: | |
9b5db89e | 6 | |
089bd866 | 7 | * Maxim MAX6874, MAX6875 |
9b5db89e | 8 | |
089bd866 | 9 | Prefix: 'max6875' |
9b5db89e | 10 | |
93ffa435 | 11 | Addresses scanned: None (see below) |
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12 | |
13 | Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf | |
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14 | |
15 | Author: Ben Gardner <bgardner@wabtec.com> | |
16 | ||
17 | ||
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18 | Description |
19 | ----------- | |
20 | ||
089bd866 | 21 | The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. |
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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 | ||
089bd866 | 25 | At reset, the MAX6875 reads the configuration EEPROM into its configuration |
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26 | registers. The chip then begins to operate according to the values in the |
27 | registers. | |
28 | ||
96d8d5ff | 29 | The Maxim MAX6874 is a similar, mostly compatible device, with more inputs |
089bd866 | 30 | and outputs: |
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31 | |
32 | =========== === === ==== | |
33 | - vin gpi vout | |
34 | =========== === === ==== | |
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35 | MAX6874 6 4 8 |
36 | MAX6875 4 3 5 | |
9b5db89e | 37 | =========== === === ==== |
089bd866 | 38 | |
93ffa435 | 39 | See the datasheet for more information. |
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40 | |
41 | ||
42 | Sysfs entries | |
43 | ------------- | |
44 | ||
93ffa435 | 45 | eeprom - 512 bytes of user-defined EEPROM space. |
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46 | |
47 | ||
48 | General Remarks | |
49 | --------------- | |
50 | ||
93ffa435 | 51 | Valid addresses for the MAX6875 are 0x50 and 0x52. |
9b5db89e | 52 | |
93ffa435 | 53 | Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. |
9b5db89e | 54 | |
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55 | The driver does not probe any address, so you explicitly instantiate the |
56 | devices. | |
93ffa435 | 57 | |
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58 | Example:: |
59 | ||
60 | $ modprobe max6875 | |
61 | $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device | |
93ffa435 | 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. | |
bd8d421f | 65 | The even-address instance is called 'max6875', the odd one is 'dummy'. |
93ffa435 | 66 | |
67 | ||
68 | Programming the chip using i2c-dev | |
69 | ---------------------------------- | |
70 | ||
71 | Use the i2c-dev interface to access and program the chips. | |
9b5db89e | 72 | |
0283fe6c | 73 | Reads and writes are performed differently depending on the address range. |
93ffa435 | 74 | |
75 | The configuration registers are at addresses 0x00 - 0x45. | |
9b5db89e | 76 | |
93ffa435 | 77 | Use i2c_smbus_write_byte_data() to write a register and |
78 | i2c_smbus_read_byte_data() to read a register. | |
9b5db89e | 79 | |
93ffa435 | 80 | The command is the register number. |
81 | ||
82 | Examples: | |
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83 | |
84 | To write a 1 to register 0x45:: | |
85 | ||
93ffa435 | 86 | i2c_smbus_write_byte_data(fd, 0x45, 1); |
87 | ||
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88 | To read register 0x45:: |
89 | ||
93ffa435 | 90 | value = i2c_smbus_read_byte_data(fd, 0x45); |
91 | ||
92 | ||
93 | The configuration EEPROM is at addresses 0x8000 - 0x8045. | |
9b5db89e | 94 | |
93ffa435 | 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. | |
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100 | The data word is the lower part of the address or'd with data << 8:: |
101 | ||
93ffa435 | 102 | cmd = address >> 8; |
103 | val = (address & 0xff) | (data << 8); | |
104 | ||
105 | Example: | |
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106 | |
107 | To write 0x5a to address 0x8003:: | |
108 | ||
93ffa435 | 109 | i2c_smbus_write_word_data(fd, 0x80, 0x5a03); |
110 | ||
111 | ||
112 | Reading data from the EEPROM is a little more complicated. | |
9b5db89e | 113 | |
93ffa435 | 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: | |
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118 | |
119 | To read data starting at offset 0x8100, first set the address:: | |
120 | ||
93ffa435 | 121 | i2c_smbus_write_byte_data(fd, 0x81, 0x00); |
122 | ||
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123 | And then read the data:: |
124 | ||
93ffa435 | 125 | value = i2c_smbus_read_byte(fd); |
126 | ||
9b5db89e | 127 | or:: |
93ffa435 | 128 | |
4b2643d7 | 129 | count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer); |
93ffa435 | 130 | |
131 | The block read should read 16 bytes. | |
9b5db89e | 132 | |
93ffa435 | 133 | 0x84 is the block read command. |
134 | ||
135 | See the datasheet for more details. | |
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