Datasheet

D7 D6 D5 D4 D3 D2 D1 D0
1 9 1 9
Ack
by
LM95231
Start by
Master
R/W
Frame 1
Serial Bus Address Byte
Frame 2
Command Byte
Ack by
LM95231
SMBCLK
SMBDAT
A5 A3 A2 A0A6 A4 A1
Stop
by
Master
LM95231
www.ti.com SNIS139E –FEBRUARY 2005–REVISED MARCH 2013
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 LM95231. The maximum resistance of the pull-up to provide a 2.1V high
level, based on LM95231 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 LM95231 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
DD
or D+ is floating, the Remote
Temperature reading is –128.000 °C if signed format is selected and +255.875 if unsigned format is selected. In
addition, the appropriate status register bits RD1M or RD2M (D1 or D0) are set. When TruTherm mode is active
the condition of diode short of D+ to D− will not be detected. Connecting a 2N3904 transistor with TruTherm
mode active may cause a detection of a diode fault.
1.7 COMMUNICATING with the LM95231
The data registers in the LM95231 are selected by the Command Register. At power-up the Command Register
is 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 LM95231 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 LM95231 will always include the address byte and the command byte. A write to any register
requires one data byte.
Reading the LM95231 can take place either of two ways:
1. If the location latched in the Command Register is correct (most of the time it is expected that the Command
Register will point to one of the Read Temperature Registers because that will be the data most frequently
read from the LM95231), then the read can simply consist of an address byte, followed by retrieving the data
byte.
2. If the Command Register needs to be set, then an address byte, command byte, repeat start, and another
address byte will accomplish a read.
The data byte has the most significant bit first. At the end of a read, the LM95231 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). When retrieving all 11 bits from a previous remote diode temperature 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.
Figure 7. Serial Bus Write to the Internal Command Register
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