path: root/Documentation/misc-devices
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authorJean Delvare <khali@linux-fr.org>2009-10-04 20:53:40 (GMT)
committerJean Delvare <khali@linux-fr.org>2009-10-04 20:53:40 (GMT)
commitf546c65cd59275c7b95eba4f9b3ab83b38a5e9cb (patch)
treee8957c44efeb5f331272d092cab974679fa896c8 /Documentation/misc-devices
parent8a0382f6fceaf0c6479e582e1054f36333ea3d24 (diff)
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>
Diffstat (limited to 'Documentation/misc-devices')
2 files changed, 204 insertions, 0 deletions
diff --git a/Documentation/misc-devices/eeprom b/Documentation/misc-devices/eeprom
new file mode 100644
index 0000000..f7e8104
--- /dev/null
+++ b/Documentation/misc-devices/eeprom
@@ -0,0 +1,96 @@
+Kernel driver eeprom
+Supported chips:
+ * Any EEPROM chip in the designated address range
+ Prefix: 'eeprom'
+ Addresses scanned: I2C 0x50 - 0x57
+ Datasheets: Publicly available from:
+ Atmel (www.atmel.com),
+ Catalyst (www.catsemi.com),
+ Fairchild (www.fairchildsemi.com),
+ Microchip (www.microchip.com),
+ Philips (www.semiconductor.philips.com),
+ Rohm (www.rohm.com),
+ ST (www.st.com),
+ Xicor (www.xicor.com),
+ and others.
+ Chip Size (bits) Address
+ 24C01 1K 0x50 (shadows at 0x51 - 0x57)
+ 24C01A 1K 0x50 - 0x57 (Typical device on DIMMs)
+ 24C02 2K 0x50 - 0x57
+ 24C04 4K 0x50, 0x52, 0x54, 0x56
+ (additional data at 0x51, 0x53, 0x55, 0x57)
+ 24C08 8K 0x50, 0x54 (additional data at 0x51, 0x52,
+ 0x53, 0x55, 0x56, 0x57)
+ 24C16 16K 0x50 (additional data at 0x51 - 0x57)
+ Sony 2K 0x57
+ Atmel 34C02B 2K 0x50 - 0x57, SW write protect at 0x30-37
+ Catalyst 34FC02 2K 0x50 - 0x57, SW write protect at 0x30-37
+ Catalyst 34RC02 2K 0x50 - 0x57, SW write protect at 0x30-37
+ Fairchild 34W02 2K 0x50 - 0x57, SW write protect at 0x30-37
+ Microchip 24AA52 2K 0x50 - 0x57, SW write protect at 0x30-37
+ ST M34C02 2K 0x50 - 0x57, SW write protect at 0x30-37
+ Frodo Looijaard <frodol@dds.nl>,
+ Philip Edelbrock <phil@netroedge.com>,
+ Jean Delvare <khali@linux-fr.org>,
+ Greg Kroah-Hartman <greg@kroah.com>,
+ IBM Corp.
+This is a simple EEPROM module meant to enable reading the first 256 bytes
+of an EEPROM (on a SDRAM DIMM for example). However, it will access serial
+EEPROMs on any I2C adapter. The supported devices are generically called
+24Cxx, and are listed above; however the numbering for these
+industry-standard devices may vary by manufacturer.
+This module was a programming exercise to get used to the new project
+organization laid out by Frodo, but it should be at least completely
+effective for decoding the contents of EEPROMs on DIMMs.
+DIMMS will typically contain a 24C01A or 24C02, or the 34C02 variants.
+The other devices will not be found on a DIMM because they respond to more
+than one address.
+DDC Monitors may contain any device. Often a 24C01, which responds to all 8
+addresses, is found.
+Recent Sony Vaio laptops have an EEPROM at 0x57. We couldn't get the
+specification, so it is guess work and far from being complete.
+The Microchip 24AA52/24LCS52, ST M34C02, and others support an additional
+software write protect register at 0x30 - 0x37 (0x20 less than the memory
+location). The chip responds to "write quick" detection at this address but
+does not respond to byte reads. If this register is present, the lower 128
+bytes of the memory array are not write protected. Any byte data write to
+this address will write protect the memory array permanently, and the
+device will no longer respond at the 0x30-37 address. The eeprom driver
+does not support this register.
+Lacking functionality:
+* Full support for larger devices (24C04, 24C08, 24C16). These are not
+typically found on a PC. These devices will appear as separate devices at
+multiple addresses.
+* Support for really large devices (24C32, 24C64, 24C128, 24C256, 24C512).
+These devices require two-byte address fields and are not supported.
+* Enable Writing. Again, no technical reason why not, but making it easy
+to change the contents of the EEPROMs (on DIMMs anyway) also makes it easy
+to disable the DIMMs (potentially preventing the computer from booting)
+until the values are restored somehow.
+After inserting the module (and any other required SMBus/i2c modules), you
+should have some EEPROM directories in /sys/bus/i2c/devices/* of names such
+as "0-0050". Inside each of these is a series of files, the eeprom file
+contains the binary data from EEPROM.
diff --git a/Documentation/misc-devices/max6875 b/Documentation/misc-devices/max6875
new file mode 100644
index 0000000..10ca43c
--- /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 <bgardner@wabtec.com>
+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
+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.
+$ 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.
+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);
+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.
+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.

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