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BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -04001Kernel driver max6875
2=====================
3
4Supported chips:
Jean Delvare089bd862005-06-23 23:37:53 +02005 * Maxim MAX6874, MAX6875
6 Prefix: 'max6875'
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -05007 Addresses scanned: None (see below)
Jean Delvare089bd862005-06-23 23:37:53 +02008 Datasheet:
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -04009 http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
10
11Author: Ben Gardner <bgardner@wabtec.com>
12
13
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -040014Description
15-----------
16
Jean Delvare089bd862005-06-23 23:37:53 +020017The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -040018It provides timed outputs that can be used as a watchdog, if properly wired.
19It also provides 512 bytes of user EEPROM.
20
Jean Delvare089bd862005-06-23 23:37:53 +020021At reset, the MAX6875 reads the configuration EEPROM into its configuration
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -040022registers. The chip then begins to operate according to the values in the
23registers.
24
Jean Delvare089bd862005-06-23 23:37:53 +020025The Maxim MAX6874 is a similar, mostly compatible device, with more intputs
26and outputs:
Jean Delvare089bd862005-06-23 23:37:53 +020027 vin gpi vout
28MAX6874 6 4 8
29MAX6875 4 3 5
30
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050031See the datasheet for more information.
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -040032
33
34Sysfs entries
35-------------
36
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050037eeprom - 512 bytes of user-defined EEPROM space.
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -040038
39
40General Remarks
41---------------
42
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050043Valid addresses for the MAX6875 are 0x50 and 0x52.
44Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
Jean Delvareb835d7f2009-10-04 22:53:41 +020045The driver does not probe any address, so you explicitly instantiate the
46devices.
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050047
48Example:
Jean Delvareb835d7f2009-10-04 22:53:41 +020049$ modprobe max6875
50$ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050051
52The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
53addresses. For example, for address 0x50, it also reserves 0x51.
Jean Delvarebd8d4212008-07-16 19:30:07 +020054The even-address instance is called 'max6875', the odd one is 'dummy'.
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050055
56
57Programming the chip using i2c-dev
58----------------------------------
59
60Use the i2c-dev interface to access and program the chips.
bgardner@wabtec.com0283fe62005-07-27 12:43:21 -050061Reads and writes are performed differently depending on the address range.
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -050062
63The configuration registers are at addresses 0x00 - 0x45.
64Use i2c_smbus_write_byte_data() to write a register and
65i2c_smbus_read_byte_data() to read a register.
66The command is the register number.
67
68Examples:
69To write a 1 to register 0x45:
70 i2c_smbus_write_byte_data(fd, 0x45, 1);
71
72To read register 0x45:
73 value = i2c_smbus_read_byte_data(fd, 0x45);
74
75
76The configuration EEPROM is at addresses 0x8000 - 0x8045.
77The user EEPROM is at addresses 0x8100 - 0x82ff.
78
79Use i2c_smbus_write_word_data() to write a byte to EEPROM.
80
81The command is the upper byte of the address: 0x80, 0x81, or 0x82.
82The data word is the lower part of the address or'd with data << 8.
83 cmd = address >> 8;
84 val = (address & 0xff) | (data << 8);
85
86Example:
87To write 0x5a to address 0x8003:
88 i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
89
90
91Reading data from the EEPROM is a little more complicated.
92Use i2c_smbus_write_byte_data() to set the read address and then
93i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
94
95Example:
96To read data starting at offset 0x8100, first set the address:
97 i2c_smbus_write_byte_data(fd, 0x81, 0x00);
98
99And then read the data
100 value = i2c_smbus_read_byte(fd);
101
102 or
103
Jean Delvare4b2643d2007-07-12 14:12:29 +0200104 count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
bgardner@wabtec.com93ffa432005-07-12 13:21:50 -0500105
106The block read should read 16 bytes.
1070x84 is the block read command.
108
109See the datasheet for more details.
BGardner@Wabtec.comc3bc4ca2005-06-03 13:03:27 -0400110