hwmon: (ds1621) Update documentation

reset. Be aware: When testing, it showed that the status of Tout can change

with neither of the alarms set.

Temperature conversion of the DS1621 takes up to 1000ms; internal access to

non-volatile registers may last for 10ms or below.

The DS1625 is pin compatible and functionally equivalent with the DS1621,

but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are

also pin compatible with the DS1621, but provide multi-resolution support.

Since there is no version or vendor identification register, there is

no unique identification for these devices. Therefore, explicit device

instantiation is required for correct device identification and functionality.

And, for correct identification and operation, each device must be

explicitly instantiated, one device per address, in this address

range: 0x48..0x4f.

instantiation is required for correct device identification and functionality

(one device per address in this address range: 0x48..0x4f).

The DS1721 is pin compatible with the DS1621, has an accuracy of +/- 1.0

degree Celsius (from -10 to +85 degrees), a minimum/maximum alarm default

setting of 75 and 80 degrees, and a maximum conversion time of 750ms.

In addition, the DS1721 supports four resolution settings from 9 to 12 bits

(defined in degrees C per LSB: 0.5, 0.25, 0.125, and 0.0625, respectively),

that are set at device power on to the highest resolution: 12-bits.

One additional note about the ds1721 is that although the data sheet says

the temperature flags (THF and TLF) are used internally, these flags do

get set and cleared as the actual temperature crosses the min or max settings.

The DS1631 and DS1731 are pin compatible with the DS1621 and feature compatible

with the DS1721. However, the DS1631 accuracy is +/- 0.5 degree Celsius (from 0

to +70 degrees), while the DS1731 accuracy is +/-1 degree Celsius (from -10 to

+85 degrees).

The DS1625 is pin compatible and functionally equivalent with the DS1621,

but the DS1621 is meant to replace it. The DS1631, DS1721, and DS1731 are

also pin compatible with the DS1621 and provide multi-resolution support.

Additionally, the DS1721 data sheet says the temperature flags (THF and TLF)

are used internally, however, these flags do get set and cleared as the actual

temperature crosses the min or max settings (which by default are set to 75

and 80 degrees respectively).

Temperature Conversion:

-----------------------

DS1621 - 750ms (older devices may take up to 1000ms)

DS1625 - 500ms

DS1631 - 93ms..750ms for 9..12 bits resolution, respectively.

DS1721 - 93ms..750ms for 9..12 bits resolution, respectively.

DS1731 - 93ms..750ms for 9..12 bits resolution, respectively.

Note:

On the DS1621, internal access to non-volatile registers may last for 10ms

or less (unverified on the other devices).

Temperature Accuracy:

---------------------

DS1621: +/- 0.5 degree Celsius (from 0 to +70 degrees)

DS1625: +/- 0.5 degree Celsius (from 0 to +70 degrees)

DS1631: +/- 0.5 degree Celsius (from 0 to +70 degrees)

DS1721: +/- 1.0 degree Celsius (from -10 to +85 degrees)

DS1731: +/- 1.0 degree Celsius (from -10 to +85 degrees)

Note:

Please refer to the device datasheets for accuracy at other temperatures.

Temperature Resolution:

-----------------------

As mentioned above, the DS1631, DS1721, and DS1731 provide multi-resolution

support, which is achieved via the R0 and R1 config register bits, where:

R0..R1

------

 0  0 => 9 bits, 0.5 degrees Celcius

 1  0 => 10 bits, 0.25 degrees Celcius

 0  1 => 11 bits, 0.125 degrees Celcius

 1  1 => 12 bits, 0.0625 degrees Celcius

Note:

At initial device power-on, the default resolution is set to 12-bits.

The resolution mode for the DS1631, DS1721, or DS1731 can be changed from

userspace, via the device 'update_interval' sysfs attribute. This attribute

Resolution    Conversion Time    Input Range

 (C/LSB)       (msec)             (msec)

--------------------------------------------

------------------------------------------------

0.5             93.75              0....94

0.25            187.5              95...187

0.125           375                188..375

0.0625          750                376..infinity

--------------------------------------

------------------------------------------------

The following examples show how the 'update_interval' attribute can be

used to change the conversion time: