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Diffstat (limited to 'Documentation/i2c')
| -rw-r--r-- | Documentation/i2c/chips/max6875 | 94 |
1 files changed, 68 insertions, 26 deletions
diff --git a/Documentation/i2c/chips/max6875 b/Documentation/i2c/chips/max6875 index b02002898a09..46b8dc34c971 100644 --- a/Documentation/i2c/chips/max6875 +++ b/Documentation/i2c/chips/max6875 @@ -4,22 +4,13 @@ Kernel driver max6875 Supported chips: * Maxim MAX6874, MAX6875 Prefix: 'max6875' - Addresses scanned: 0x50, 0x52 + Addresses scanned: None (see below) Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf Author: Ben Gardner <bgardner@wabtec.com> -Module Parameters ------------------ - -* allow_write int - Set to non-zero to enable write permission: - *0: Read only - 1: Read and write - - Description ----------- @@ -33,34 +24,85 @@ registers. The Maxim MAX6874 is a similar, mostly compatible device, with more intputs and outputs: - vin gpi vout MAX6874 6 4 8 MAX6875 4 3 5 -MAX6874 chips can have four different addresses (as opposed to only two for -the MAX6875). The additional addresses (0x54 and 0x56) are not probed by -this driver by default, but the probe module parameter can be used if -needed. - -See the datasheet for details on how to program the EEPROM. +See the datasheet for more information. Sysfs entries ------------- -eeprom_user - 512 bytes of user-defined EEPROM space. Only writable if - allow_write was set and register 0x43 is 0. - -eeprom_config - 70 bytes of config EEPROM. Note that changes will not get - loaded into register space until a power cycle or device reset. - -reg_config - 70 bytes of register space. Any changes take affect immediately. +eeprom - 512 bytes of user-defined EEPROM space. General Remarks --------------- -A typical application will require that the EEPROMs be programmed once and -never altered afterwards. +Valid addresses for the MAX6875 are 0x50 and 0x52. +Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56. +The driver does not probe any address, so you must force the address. + +Example: +$ modprobe max6875 force=0,0x50 + +The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple +addresses. For example, for address 0x50, it also reserves 0x51. +The even-address instance is called 'max6875', the odd one is 'max6875-dummy'. + + +Programming the chip using i2c-dev +---------------------------------- + +Use the i2c-dev interface to access and program the chips. +Reads and write are performed differently depending on the address range. + +The configuration registers are at addresses 0x00 - 0x45. +Use i2c_smbus_write_byte_data() to write a register and +i2c_smbus_read_byte_data() to read a register. +The command is the register number. + +Examples: +To write a 1 to register 0x45: + i2c_smbus_write_byte_data(fd, 0x45, 1); + +To read register 0x45: + value = i2c_smbus_read_byte_data(fd, 0x45); + + +The configuration EEPROM is at addresses 0x8000 - 0x8045. +The user EEPROM is at addresses 0x8100 - 0x82ff. + +Use i2c_smbus_write_word_data() to write a byte to EEPROM. + +The command is the upper byte of the address: 0x80, 0x81, or 0x82. +The data word is the lower part of the address or'd with data << 8. + cmd = address >> 8; + val = (address & 0xff) | (data << 8); + +Example: +To write 0x5a to address 0x8003: + i2c_smbus_write_word_data(fd, 0x80, 0x5a03); + + +Reading data from the EEPROM is a little more complicated. +Use i2c_smbus_write_byte_data() to set the read address and then +i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data. + +Example: +To read data starting at offset 0x8100, first set the address: + i2c_smbus_write_byte_data(fd, 0x81, 0x00); + +And then read the data + value = i2c_smbus_read_byte(fd); + + or + + count = i2c_smbus_read_i2c_block_data(fd, 0x84, buffer); + +The block read should read 16 bytes. +0x84 is the block read command. + +See the datasheet for more details. |