From f546c65cd59275c7b95eba4f9b3ab83b38a5e9cb Mon Sep 17 00:00:00 2001 From: Jean Delvare Date: Sun, 4 Oct 2009 22:53:40 +0200 Subject: i2c: Move misc devices documentation Some times ago the eeprom and max6875 drivers moved to drivers/misc/eeprom, but their documentation did not follow. It's finally time to get rid of Documentation/i2c/chips. Signed-off-by: Jean Delvare Cc: Ben Gardner Acked-by: Wolfram Sang --- Documentation/misc-devices/max6875 | 108 +++++++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) create mode 100644 Documentation/misc-devices/max6875 (limited to 'Documentation/misc-devices/max6875') diff --git a/Documentation/misc-devices/max6875 b/Documentation/misc-devices/max6875 new file mode 100644 index 000000000000..10ca43cd1a72 --- /dev/null +++ b/Documentation/misc-devices/max6875 @@ -0,0 +1,108 @@ +Kernel driver max6875 +===================== + +Supported chips: + * Maxim MAX6874, MAX6875 + Prefix: 'max6875' + Addresses scanned: None (see below) + Datasheet: + http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf + +Author: Ben Gardner + + +Description +----------- + +The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor. +It provides timed outputs that can be used as a watchdog, if properly wired. +It also provides 512 bytes of user EEPROM. + +At reset, the MAX6875 reads the configuration EEPROM into its configuration +registers. The chip then begins to operate according to the values in the +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 + +See the datasheet for more information. + + +Sysfs entries +------------- + +eeprom - 512 bytes of user-defined EEPROM space. + + +General Remarks +--------------- + +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 'dummy'. + + +Programming the chip using i2c-dev +---------------------------------- + +Use the i2c-dev interface to access and program the chips. +Reads and writes 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, 16, buffer); + +The block read should read 16 bytes. +0x84 is the block read command. + +See the datasheet for more details. + -- cgit v1.2.3