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authorJean Delvare <khali@linux-fr.org>2009-10-05 00:53:40 +0400
committerJean Delvare <khali@linux-fr.org>2009-10-05 00:53:40 +0400
commitf546c65cd59275c7b95eba4f9b3ab83b38a5e9cb (patch)
treee8957c44efeb5f331272d092cab974679fa896c8 /Documentation/misc-devices/max6875
parent8a0382f6fceaf0c6479e582e1054f36333ea3d24 (diff)
downloadlinux-f546c65cd59275c7b95eba4f9b3ab83b38a5e9cb.tar.xz
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 <khali@linux-fr.org> Cc: Ben Gardner <gardner.ben@gmail.com> Acked-by: Wolfram Sang <w.sang@pengutronix.de>
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+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 <bgardner@wabtec.com>
+
+
+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.
+