NVT210
When reading data from a register there are two possibilities.
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose ALERT output is low responds
to the alert response address and the master reads
its device address. As the device address is seven
bits, an LSB of 1 is added. The address of the
device is now known and it can be interrogated in
the usual way.
• If the address pointer register value of the NVT210 is
unknown or not the desired value, it is first necessary to
set it to the correct value before data can be read from
the desired data register. This is done by writing to the
NVT210 as before, but only the data byte containing
the register read address is sent, because data is not to
be written to the register see Figure 16.
A read operation is then performed consisting of the
serial bus address, R/W bit set to 1, followed by the
data byte read from the data register see Figure 17.
4. If more than one device’s ALERT output is low,
the one with the lowest device address takes
• If the address pointer register is known to be at the
desired address, data can be read from the
2
priority, in accordance with normal SMBus/I C
corresponding data register without first writing to the
address pointer register and the bus transaction shown
in Figure 16 can be omitted.
arbitration.
Once the NVT210 has responded to the alert response
address, it resets its ALERT output, provided that the error
condition that caused the ALERT no longer exists. If the
SMBALERT line remains low, the master sends the ARA
again, and so on until all devices whose ALERT outputs
were low have responded.
Notes:
• It is possible to read a data byte from a data register
without first writing to the address pointer register.
However, if the address pointer register is already at the
correct value, it is not possible to write data to a register
without writing to the address pointer register because
the first data byte of a write is always written to the
address pointer register.
• Some of the registers have different addresses for read
and write operations. The write address of a register
must be written to the address pointer if data is to be
written to that register, but it may not be possible to
read data from that address. The read address of a
register must be written to the address pointer before
data can be read from that register.
Low Power Standby Mode
The NVT210 can be put into low power standby mode by
setting Bit 6 of the configuration register. When Bit 6 is low,
the NVT210 operates normally. When Bit 6 is high, the ADC
is inhibited, and any conversion in progress is terminated
without writing the result to the corresponding value
2
register. However, the SMBus/I C is still enabled. Power
consumption in the standby mode is reduced to 5 mA if there
2
is no SMBus/I C activity, or 30 mA if there are clock and
data signals on the bus.
When the device is in standby mode, it is possible to
initiate a one-shot conversion of both channels by writing to
the one-shot register (Address 0x0F), after which the device
returns to standby. It does not matter what is written to the
one-shot register, all data written to it is ignored. It is also
possible to write new values to the limit register while in
standby mode. If the values stored in the temperature value
registers are outside the new limits, an ALERT is generated,
even though the NVT210 is still in standby.
ALERT Output
This is applicable when Pin 6 is configured as an ALERT
output. The ALERT output goes low whenever an
out-of-limit measurement is detected, or if the remote
temperature sensor is open circuit. It is an open-drain output
and requires a pullup resistor to V . Several ALERT outputs
can be wire-OR’ed together, so that the common line goes
low if one or more of the ALERT outputs goes low.
DD
The ALERT output can be used as an interrupt signal to a
processor, or as an SMBALERT. Slave devices on the
Sensor Fault Detection
2
SMBus/I C cannot normally signal to the bus master that
At its D+ input, the NVT210 contains internal sensor fault
detection circuitry. This circuit can detect situations where
an external remote diode is either not connected or
incorrectly connected to the NVT210. A simple voltage
they want to talk, but the SMBALERT function allows them
to do so.
One or more ALERT outputs can be connected to a
common SMBALERT line that is connected to the master.
When the SMBALERT line is pulled low by one of the
devices, the following procedure occurs (see Figure 18):
comparator trips if the voltage at D+ exceeds V − 1.0 V
DD
(typical), signifying an open circuit between D+ and D−.
The output of this comparator is checked when a conversion
is initiated. Bit 2 of the status register (open flag) is set if a
fault is detected. If the ALERT pin is enabled, setting this
flag causes ALERT to assert low.
If the user does not wish to use an external sensor with the
NVT210, tie the D+ and D− inputs together to prevent
continuous setting of the open flag.
MASTER RECEIVES SMBALERT
ALERT RESPONSE
ADDRESS
DEVICE
NO
ACK
START
RD ACK
STOP
ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
DEVICE SENDS
ITS ADDRESS
Figure 18. Use of SMBALERT
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