lm95221cimm-eng National Semiconductor Corporation, lm95221cimm-eng Datasheet - Page 9

• Manufacturer Part Number: lm95221cimm-eng
• Description: Dual Remote Diode Digital Temperature Sensor With Smbus Interface
• Manufacturer: National Semiconductor Corporation

1.0 Functional Description
1.5 SMBDAT OPEN-DRAIN OUTPUT
The SMBDAT output is an open-drain output and does not
have internal pull-ups. A “high” level will not be observed on
this pin until pull-up current is provided by some external
source, typically a pull-up resistor. Choice of resistor value
depends on many system factors but, in general, the pull-up
resistor should be as large as possible without effecting the
SMBus desired data rate. This will minimize any internal
temperature reading errors due to internal heating of the
LM95221. The maximum resistance of the pull-up to provide
a 2.1V high level, based on LM95221 specification for High
Level Output Current with the supply voltage at 3.0V, is
82kΩ(5%) or 88.7kΩ(1%).
1.6 DIODE FAULT DETECTION
The LM95221 is equipped with operational circuitry designed
to detect fault conditions concerning the remote diodes. In
the event that the D+ pin is detected as shorted to GND, D−,
V
unsigned format is selected. In addition, the appropriate
status register bits RD1M or RD2M (D1 or D0) are set.
1.7 COMMUNICATING with the LM95221
The data registers in the LM95221 are selected by the
Command Register. At power-up the Command Register is
–128.000 ˚C if signed format is selected and +255.875 if
DD
Temperature
or D+ is floating, the Remote Temperature reading is
−0.25˚C
−25˚C
−55˚C
−1˚C
1100 1001 0000 0000
1110 0111 0000 0000
1111 1111 1100 0000
1111 1111 0000 0000
Binary
Digital Output
(Continued)
FFE0h
C900h
FF00h
E700h
Hex
9
set to “00”, the location for the Read Local Temperature
Register. The Command Register latches the last location it
was set to. Each data register in the LM95221 falls into one
of four types of user accessibility:
1. Read only
2. Write only
3. Write/Read same address
4. Write/Read different address
A Write to the LM95221 will always include the address byte
and the command byte. A write to any register requires one
data byte.
Reading the LM95221 can take place either of two ways:
1. If the location latched in the Command Register is cor-
2. If the Command Register needs to be set, then an
The data byte has the most significant bit first. At the end of
a read, the LM95221 can accept either acknowledge or No
Acknowledge from the Master (No Acknowledge is typically
used as a signal for the slave that the Master has read its
last byte). It takes the LM95221 66 ms to measure the
temperature of the remote diodes and internal diode. When
retrieving all 11 bits from a previous remote diode tempera-
ture measurement, the master must insure that all 11 bits are
from the same temperature conversion. This may be
achieved by reading the MSB register first. The LSB will be
locked after the MSB is read. The LSB will be unlocked after
being read. If the user reads MSBs consecutively, each time
the MSB is read, the LSB associated with that temperature
will be locked in and override the previous LSB value
locked-in.
rect (most of the time it is expected that the Command
Register will point to one of the Read Temperature Reg-
isters because that will be the data most frequently read
from the LM95221), then the read can simply consist of
an address byte, followed by retrieving the data byte.
address byte, command byte, repeat start, and another
address byte will accomplish a read.
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