path: root/Documentation/i2c
diff options
authorbgardner@wabtec.com <bgardner@wabtec.com>2005-07-12 13:21:50 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2005-09-05 09:14:03 -0700
commit93ffa435147abd47ebd7d7d24176b3c653aef940 (patch)
tree451f9bdfa2ec7e2c4399dd6ca3cc3c97f12c27b9 /Documentation/i2c
parentbc769ff8f5f6e3d249bfde082653e5bf1c2b5698 (diff)
[PATCH] I2C: update max6875 documentation
Updates to the max6875 driver documentation. This brings the documentation in sync with the code, which was recently simplified. This patch is based off 2.6.13-rc2-mm2. Signed-off-by: Ben Gardner <bgardner@wabtec.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/i2c')
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)
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
@@ -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
-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.
+$ 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.
+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, buffer);
+The block read should read 16 bytes.
+0x84 is the block read command.
+See the datasheet for more details.