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136 lines
3.2 KiB
136 lines
3.2 KiB
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Kernel driver max6875 |
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Supported chips: |
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* Maxim MAX6874, MAX6875 |
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Prefix: 'max6875' |
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Addresses scanned: None (see below) |
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Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf |
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Author: Ben Gardner <[email protected]> |
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Description |
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----------- |
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The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. |
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It provides timed outputs that can be used as a watchdog, if properly wired. |
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It also provides 512 bytes of user EEPROM. |
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At reset, the MAX6875 reads the configuration EEPROM into its configuration |
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registers. The chip then begins to operate according to the values in the |
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registers. |
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The Maxim MAX6874 is a similar, mostly compatible device, with more inputs |
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and outputs: |
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=========== === === ==== |
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- vin gpi vout |
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=========== === === ==== |
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MAX6874 6 4 8 |
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MAX6875 4 3 5 |
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=========== === === ==== |
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See the datasheet for more information. |
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Sysfs entries |
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------------- |
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eeprom - 512 bytes of user-defined EEPROM space. |
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General Remarks |
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--------------- |
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Valid addresses for the MAX6875 are 0x50 and 0x52. |
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Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. |
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The driver does not probe any address, so you explicitly instantiate the |
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devices. |
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Example:: |
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$ modprobe max6875 |
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$ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device |
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The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple |
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addresses. For example, for address 0x50, it also reserves 0x51. |
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The even-address instance is called 'max6875', the odd one is 'dummy'. |
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Programming the chip using i2c-dev |
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---------------------------------- |
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Use the i2c-dev interface to access and program the chips. |
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Reads and writes are performed differently depending on the address range. |
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The configuration registers are at addresses 0x00 - 0x45. |
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Use i2c_smbus_write_byte_data() to write a register and |
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i2c_smbus_read_byte_data() to read a register. |
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The command is the register number. |
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Examples: |
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To write a 1 to register 0x45:: |
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i2c_smbus_write_byte_data(fd, 0x45, 1); |
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To read register 0x45:: |
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value = i2c_smbus_read_byte_data(fd, 0x45); |
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The configuration EEPROM is at addresses 0x8000 - 0x8045. |
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The user EEPROM is at addresses 0x8100 - 0x82ff. |
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Use i2c_smbus_write_word_data() to write a byte to EEPROM. |
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The command is the upper byte of the address: 0x80, 0x81, or 0x82. |
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The data word is the lower part of the address or'd with data << 8:: |
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cmd = address >> 8; |
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val = (address & 0xff) | (data << 8); |
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Example: |
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To write 0x5a to address 0x8003:: |
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i2c_smbus_write_word_data(fd, 0x80, 0x5a03); |
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Reading data from the EEPROM is a little more complicated. |
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Use i2c_smbus_write_byte_data() to set the read address and then |
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i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data. |
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Example: |
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To read data starting at offset 0x8100, first set the address:: |
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i2c_smbus_write_byte_data(fd, 0x81, 0x00); |
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And then read the data:: |
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value = i2c_smbus_read_byte(fd); |
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or:: |
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count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer); |
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The block read should read 16 bytes. |
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0x84 is the block read command. |
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See the datasheet for more details. |
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