LM95234_07 NSC [National Semiconductor], LM95234_07 Datasheet - Page 16

• Manufacturer Part Number: LM95234_07
• Description: Quad Remote Diode and Local Temperature Sensor with SMBus Interface and TruTherm Technology
• Manufacturer: NSC [National Semiconductor]

www.national.com
Limit assignments for each TCRIT output pin:
The TCRIT response diagram of Figure 7 shows the local
temperature interaction with the Tcrit limit and hysteresis val-
ue. As can be seen in the diagram when the local temperature
exceeds the Tcrit limit register value the LTn Status bit is set
and the T_CRITn output(s) is/are activated. The Status bit(s)
and outputs are not deactivated until the temperature goes
below the value calculated by subtracting the Common Hys-
teresis value programmed from the limit. This diagram mainly
shows an example function of the hysteresis and is not meant
to show complete function of the possible settings and options
of all the TCRIT outputs and limit values.
1.10 DIODE FAULT DETECTION
The LM95234 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
is –128.000 °C if signed format is selected and 0 °C if un-
signed format is selected. In addition, the appropriate status
register bits RD1M or RD2M (D1 or D0) are set.
1.11 COMMUNICATING with the LM95234
The data registers in the LM95234 are selected by the Com-
mand 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 LM95234 falls into one of three types
of user accessibility:
1.
2.
3.
Remote 4
Remote 3
Remote 2
Remote 1
Local
DD
Read only
Write only
Write/Read same address
or D+ is floating, the Remote Temperature reading
TCRIT1
Remote 4
Tcrit Limit
Remote 3
Tcrit Limit
Remote 2
Tcrit-1 Limit
Remote 1
Tcrit-1 Limit
Local
Tcrit Limit
FIGURE 7. TCRIT response diagram (masking options not included)
TCRIT2
Remote 4
Tcrit Limit
Remote 3
Tcrit Limit
Remote 2
Tcrit-2 Limit
Remote 1
Tcrit-2 Limit
Local
Tcrit Limit
TCRIT3
Remote 4
Tcrit Limit
Remote 3
Tcrit Limit
Remote 2
Tcrit-2 Limit
Remote 1
Tcrit-2 Limit
Local
Tcrit Limit
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A Write to the LM95234 will always include the address byte
and the command byte. A write to any register requires one
data byte.
Reading the LM95234 can take place either of two ways:
1.
2.
The data byte has the most significant bit first. At the end of
a read, the LM95234 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 LM95234 190 ms (typical, all channels en-
abled) to measure the temperature of the remote diodes and
internal diode. When retrieving all 11 bits from a previous re-
mote diode temperature measurement, the master must in-
sure that all 11 bits are from the same temperature
conversion. This may be achieved by reading the MSB reg-
ister 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 pre-
vious LSB value locked-in.
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 LM95234), then the read can simply
consist of an address byte, followed by retrieving the data
byte.
If the Command Register needs to be set, then an
address byte, command byte, repeat start, and another
address byte will accomplish a read.
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