MAX6698
for remote diode 1 can be read from the extended tem-
perature register. If extended resolution is desired, the
extended resolution register should be read first. This
prevents the most significant bits from being overwritten
by new conversion results until they have been read. If
the most significant bits have not been read within an
SMBus timeout period (nominally 25ms), normal updat-
ing continues. Table 1 shows themistor voltage data for-
mat. Table 2 shows the main temperature register (high
byte) data format. Table 3 shows the extended resolu-
tion temperature register (low byte) data format.
Diode Fault Detection
If a channel’s input DXP_ and DXN_ are left open, the
MAX6698 detects a diode fault. An open diode fault
does not cause either ALERT or OVERT to assert. A bit
in the status register for the corresponding channel is
set to 1 and the temperature data for the channel is
stored as all 1s (FFh). It takes approximately 4ms for
the MAX6698 to detect a diode fault. Once a diode fault
is detected, the MAX6698 goes to the next channel in
the conversion sequence. Depending on operating
conditions, a shorted diode may or may not cause
ALERT or OVERT to assert, so if a channel will not be
used, disconnect its DXP and DXN inputs.
Alarm Threshold Registers
There are 11 alarm threshold registers that store over-
temperature ALERT and OVERT threshold values.
Seven of these registers are dedicated to store one
local alert temperature threshold limit, three remote alert
temperature threshold limits, and three thermistor volt-
age threshold limits (see the
ALERT
Interrupt Mode sec-
tion). The remaining four registers are dedicated to
remote-diode channel 1, and three thermistor channels
1, 2, and 3 to store overtemperature threshold limits
(see the
OVERT
Overtemperature Alarm section).
Access to these registers is provided through the
SMBus interface.
7-Channel Precision Remote-Diode, Thermistor,
and Local Temperature Monitor
8 _______________________________________________________________________________________
Figure 2. SMBus Protocols
Write Byte Format
Read Byte Format
Send Byte Format
Receive Byte Format
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave Address: equiva-
lent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
Command Byte: sends com-
mand with no data, usually
used for one-shot command
Data Byte: reads data from
the register commanded
by the last read byte or
write byte transmission;
also used for SMBus alert
response return address
S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged
S ADDRESS RD ACK DATA /// P
7 bits 8 bits
WRS ACK COMMAND ACK P
8 bits
ADDRESS
7 bits
P
1
ACKDATA
8 bits
ACKCOMMAND
8 bits
ACKWRADDRESS
7 bits
S
S ADDRESS WR ACK COMMAND ACK S ADDRESS
7 bits8 bits7 bits
RD ACK DATA
8 bits
/// P
