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(Phil) Added documentation for the ADM1021.

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git-svn-id: http://lm-sensors.org/svn/lm-sensors/trunk@198 7894878c-1315-0410-8ee3-d5d059ff63e0
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Philip Edelbrock
1999-02-07 01:28:20 +00:00
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This file documents the adm1021 directories for the Analog Devices ADM1021
temperature sensor chip.
There will be one directory created for each detected ADm1021 chip. As
ADM1021 chips can only be on a SMBus, they will be called adm1021-i2c-?-??, with
the first question mark being the number of the i2c bus (see /proc/bus/i2c
for a list of them, if i2c-proc is loaded), and the SMBus (I2C) address
of the chip at the end. An ADM1021 is uniquely characterised with these
two numbers. /proc/sys/dev/sensors/chips contains the SYSCTL values for
all chip directories.
Within each LM75 directory, you can find the following files:
* die_code (ADM1021_SYSCTL_DIE_CODE)
Silicon die (mask) revision code. This driver was written using a sample
device of die code 3. Normally this kind of information isn't reported
in its own proc file, but for a device this simple I didn't think it
would hurt.
* status (ADM1021_SYSCTL_STATUS)
This is an intergral number composed of 8-bits, which indicate the
different alarms and conversion status's of the adm1021. Here is what
each bit indicates:
7 BUSY 1 When ADC Converting.
6 LHIGH# 1 When Local High Temp Limit Tripped.
5 LLOW# 1 When Local Low Temp Limit Tripped.
4 RHIGH# 1 When Remote High Temp Limit Tripped.
3 RLOW# 1 When Remote Low Temp Limit Tripped.
2 OPEN# 1 When Remote Sensor Open-Circuit. (i.e., no connected remote sensor)
1-0 Reserved.
Note: # - These flags stay high until the status register is read or they are reset by POR.
* temp (ADM1021_SYSCTL_TEMP)
A list of three numbers. The first number is the Overtemperature Shutdown
value, the second number is Low limit value, and the third number is the
current temperature. The first two values can be modified. Each value can
be set and read to full-degree accuracy. All values are in degrees Celcius.
An alarm is issued (usually to a connected ADM9240) when the temperature
gets higher then the Overtemperature Shutdown value; it stays on until
the temperature falls back below the Overtemperature Shutdown value.
NOTE: This is different than the way most remote temperature sensors work
(e.g. the LM75), they usually use the lower limit to clear the alarm set
from initially going above the Overtemperature limit. Instead, the
ADM1021 acts much the way that voltage limits work on, say, the LM78 or
ADM9240. A disadvantage to this is that the alarm doesn't have a
hysteresis (like a shmidt-trigger or thermostat) type of function for
doing things like controlling over-heat fans and such. Instead, the
lower limit can be used to signal an alarm if (goodness forbid!) the
computer gets too cold.
If accessed through sysctl, this is a list of longs, each being the
temperature times 10.
* remote_temp (ADM1021_SYSCTL_REMOTE_TEMP)
Works exactly the same way as 'temp', but uses an external temperature
probe for the sensing. The temperature probe is of a silicon diode type
and not of a thermal-resistive type. A probe can easily be made from a
common transister (see the ADM1021 for qualification specs) by shorting
the base to the collector. From the docs: "Transistors such as 2N3904,
2N3906 or equivalents in SOT-23 package are suitable to use."
The data for each ADM1021 is updated each 1.5 seconds, but only if it is actually
read. And, any alarms triggered between reads which always be present in
the next read just after the alarm was triggered (regardless if the alarm
situation has been resolved or not).
This driver was written and is maintained by Philip Edelbrock
<phil@netroedge.com>. Please send corrections/comments to him. For
further technical information on this chip, please get the Acrobat PDF
documentation available from www.analog.com. We'd also like to thank
Analog Devices for helping us with correspondance and free samples to make
this driver (and other Analog Devices drivers) possible.