Documentation/hwmon/ds1621 - linux - Git at Google


            
            Kernel driver ds1621

            
            ====================


            Supported chips:

            
              * Dallas Semiconductor DS1621

            
                Prefix: 'ds1621'

            
                Addresses scanned: I2C 0x48 - 0x4f

            
                Datasheet: Publicly available at the Dallas Semiconductor website

            
                           http://www.dalsemi.com/

            
              * Dallas Semiconductor DS1625

            
                Prefix: 'ds1621'

            
                Addresses scanned: I2C 0x48 - 0x4f

            
                Datasheet: Publicly available at the Dallas Semiconductor website

            
                           http://www.dalsemi.com/


            Authors:

            
                    Christian W. Zuckschwerdt <zany@triq.net>

            
                    valuable contributions by Jan M. Sendler <sendler@sendler.de>

            
                    ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>

            
                    with the help of Jean Delvare <khali@linux-fr.org>


            Module Parameters

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


            * polarity int

            
              Output's polarity: 0 = active high, 1 = active low


            Description

            
            -----------


            The DS1621 is a (one instance) digital thermometer and thermostat. It has

            
            both high and low temperature limits which can be user defined (i.e.

            
            programmed into non-volatile on-chip registers). Temperature range is -55

            
            degree Celsius to +125 in 0.5 increments. You may convert this into a

            
            Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity

            
            parameter is not provided, original value is used.


            As for the thermostat, behavior can also be programmed using the polarity

            
            toggle. On the one hand ("heater"), the thermostat output of the chip,

            
            Tout, will trigger when the low limit temperature is met or underrun and

            
            stays high until the high limit is met or exceeded. On the other hand

            
            ("cooler"), vice versa. That way "heater" equals "active low", whereas

            
            "conditioner" equals "active high". Please note that the DS1621 data sheet

            
            is somewhat misleading in this point since setting the polarity bit does

            
            not simply invert Tout.


            A second thing is that, during extensive testing, Tout showed a tolerance

            
            of up to +/- 0.5 degrees even when compared against precise temperature

            
            readings. Be sure to have a high vs. low temperature limit gap of al least

            
            1.0 degree Celsius to avoid Tout "bouncing", though!


            As for alarms, you can read the alarm status of the DS1621 via the 'alarms'

            
            /sys file interface. The result consists mainly of bit 6 and 5 of the

            
            configuration register of the chip; bit 6 (0x40 or 64) is the high alarm

            
            bit and bit 5 (0x20 or 32) the low one. These bits are set when the high or

            
            low limits are met or exceeded and are reset by the module as soon as the

            
            respective temperature ranges are left.


            The alarm registers are in no way suitable to find out about the actual

            
            status of Tout. They will only tell you about its history, whether or not

            
            any of the limits have ever been met or exceeded since last power-up or

            
            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.


            High Accuracy Temperature Reading

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


            As said before, the temperature issued via the 9-bit i2c-bus data is

            
            somewhat arbitrary. Internally, the temperature conversion is of a

            
            different kind that is explained (not so...) well in the DS1621 data sheet.

            
            To cut the long story short: Inside the DS1621 there are two oscillators,

            
            both of them biassed by a temperature coefficient.


            Higher resolution of the temperature reading can be achieved using the

            
            internal projection, which means taking account of REG_COUNT and REG_SLOPE

            
            (the driver manages them):


            Taken from Dallas Semiconductors App Note 068: 'Increasing Temperature

            
            Resolution on the DS1620' and App Note 105: 'High Resolution Temperature

            
            Measurement with Dallas Direct-to-Digital Temperature Sensors'


            - Read the 9-bit temperature and strip the LSB (Truncate the .5 degs)

            
            - The resulting value is TEMP_READ.

            
            - Then, read REG_COUNT.

            
            - And then, REG_SLOPE.


                  TEMP = TEMP_READ - 0.25 + ((REG_SLOPE - REG_COUNT) / REG_SLOPE)


            Note that this is what the DONE bit in the DS1621 configuration register is

            
            good for: Internally, one temperature conversion takes up to 1000ms. Before

            
            that conversion is complete you will not be able to read valid things out

            
            of REG_COUNT and REG_SLOPE. The DONE bit, as you may have guessed by now,

            
            tells you whether the conversion is complete ("done", in plain English) and

            
            thus, whether the values you read are good or not.


            The DS1621 has two modes of operation: "Continuous" conversion, which can

            
            be understood as the default stand-alone mode where the chip gets the

            
            temperature and controls external devices via its Tout pin or tells other

            
            i2c's about it if they care. The other mode is called "1SHOT", that means

            
            that it only figures out about the temperature when it is explicitly told

            
            to do so; this can be seen as power saving mode.


            Now if you want to read REG_COUNT and REG_SLOPE, you have to either stop

            
            the continuous conversions until the contents of these registers are valid,

            
            or, in 1SHOT mode, you have to have one conversion made.
	Kernel driver ds1621
	====================

	Supported chips:
	* Dallas Semiconductor DS1621
	Prefix: 'ds1621'
	Addresses scanned: I2C 0x48 - 0x4f
	Datasheet: Publicly available at the Dallas Semiconductor website
	http://www.dalsemi.com/
	* Dallas Semiconductor DS1625
	Prefix: 'ds1621'
	Addresses scanned: I2C 0x48 - 0x4f
	Datasheet: Publicly available at the Dallas Semiconductor website
	http://www.dalsemi.com/

	Authors:
	Christian W. Zuckschwerdt <zany@triq.net>
	valuable contributions by Jan M. Sendler <sendler@sendler.de>
	ported to 2.6 by Aurelien Jarno <aurelien@aurel32.net>
	with the help of Jean Delvare <khali@linux-fr.org>

	Module Parameters
	------------------

	* polarity int
	Output's polarity: 0 = active high, 1 = active low

	Description
	-----------

	The DS1621 is a (one instance) digital thermometer and thermostat. It has
	both high and low temperature limits which can be user defined (i.e.
	programmed into non-volatile on-chip registers). Temperature range is -55
	degree Celsius to +125 in 0.5 increments. You may convert this into a
	Fahrenheit range of -67 to +257 degrees with 0.9 steps. If polarity
	parameter is not provided, original value is used.

	As for the thermostat, behavior can also be programmed using the polarity
	toggle. On the one hand ("heater"), the thermostat output of the chip,
	Tout, will trigger when the low limit temperature is met or underrun and
	stays high until the high limit is met or exceeded. On the other hand
	("cooler"), vice versa. That way "heater" equals "active low", whereas
	"conditioner" equals "active high". Please note that the DS1621 data sheet
	is somewhat misleading in this point since setting the polarity bit does
	not simply invert Tout.

	A second thing is that, during extensive testing, Tout showed a tolerance
	of up to +/- 0.5 degrees even when compared against precise temperature
	readings. Be sure to have a high vs. low temperature limit gap of al least
	1.0 degree Celsius to avoid Tout "bouncing", though!

	As for alarms, you can read the alarm status of the DS1621 via the 'alarms'
	/sys file interface. The result consists mainly of bit 6 and 5 of the
	configuration register of the chip; bit 6 (0x40 or 64) is the high alarm
	bit and bit 5 (0x20 or 32) the low one. These bits are set when the high or
	low limits are met or exceeded and are reset by the module as soon as the
	respective temperature ranges are left.

	The alarm registers are in no way suitable to find out about the actual
	status of Tout. They will only tell you about its history, whether or not
	any of the limits have ever been met or exceeded since last power-up or
	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.

	High Accuracy Temperature Reading
	---------------------------------

	As said before, the temperature issued via the 9-bit i2c-bus data is
	somewhat arbitrary. Internally, the temperature conversion is of a
	different kind that is explained (not so...) well in the DS1621 data sheet.
	To cut the long story short: Inside the DS1621 there are two oscillators,
	both of them biassed by a temperature coefficient.

	Higher resolution of the temperature reading can be achieved using the
	internal projection, which means taking account of REG_COUNT and REG_SLOPE
	(the driver manages them):

	Taken from Dallas Semiconductors App Note 068: 'Increasing Temperature
	Resolution on the DS1620' and App Note 105: 'High Resolution Temperature
	Measurement with Dallas Direct-to-Digital Temperature Sensors'

	- Read the 9-bit temperature and strip the LSB (Truncate the .5 degs)
	- The resulting value is TEMP_READ.
	- Then, read REG_COUNT.
	- And then, REG_SLOPE.

	TEMP = TEMP_READ - 0.25 + ((REG_SLOPE - REG_COUNT) / REG_SLOPE)

	Note that this is what the DONE bit in the DS1621 configuration register is
	good for: Internally, one temperature conversion takes up to 1000ms. Before
	that conversion is complete you will not be able to read valid things out
	of REG_COUNT and REG_SLOPE. The DONE bit, as you may have guessed by now,
	tells you whether the conversion is complete ("done", in plain English) and
	thus, whether the values you read are good or not.

	The DS1621 has two modes of operation: "Continuous" conversion, which can
	be understood as the default stand-alone mode where the chip gets the
	temperature and controls external devices via its Tout pin or tells other
	i2c's about it if they care. The other mode is called "1SHOT", that means
	that it only figures out about the temperature when it is explicitly told
	to do so; this can be seen as power saving mode.

	Now if you want to read REG_COUNT and REG_SLOPE, you have to either stop
	the continuous conversions until the contents of these registers are valid,
	or, in 1SHOT mode, you have to have one conversion made.