MAX6636
ALERT
Response Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex logic needed to be a bus master.
Upon receiving an interrupt signal, the host master can
broadcast a receive byte transmission to the alert
response slave address (see the
Slave Address
sec-
tion). Then, any slave device that generated an inter-
rupt attempts to identify itself by putting its own
address on the bus.
The alert response can activate several different slave
devices simultaneously, similar to the I
2
C General Call.
If more than one slave attempts to respond, bus arbitra-
tion rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledgment and continues to hold the ALERT line
low until cleared. (The conditions for clearing an alert
vary depending on the type of slave device.)
Successful completion of the alert response protocol
clears the output latch. If the condition that caused the
alert still exists, the MAX6636 reasserts the ALERT
interrupt at the end of the next conversion.
OVERT
Overtemperature Alarms
The MAX6636 has four overtemperature registers that
store remote alarm threshold data for the OVERT output.
OVERT is asserted when a channel’s measured temper-
ature is greater than the value stored in the correspond-
ing threshold register. OVERT remains asserted until the
temperature drops below the programmed threshold
minus 4°C hysteresis. An overtemperature output can
be used to activate a cooling fan, send a warning, initi-
ate clock throttling, or trigger a system shutdown to pre-
vent component damage. See Table 3 for the POR state
of the overtemperature threshold registers.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the various other registers within the
MAX6636. This register’s POR state is 0000 0000.
Configuration Byte Functions
There are three read-write configuration registers
(Tables 4, 5, and 6) that can be used to control the
MAX6636’s operation.
Configuration 1 Register
The configuration 1 register (Table 4) has several func-
tions. Bit 7 (MSB) is used to put the MAX6636 either in
software standby mode (STOP) or continuous conver-
sion mode. Bit 6 resets all registers to their power-on-
reset conditions and then clears itself. Bit 5 disables the
SMBus timeout. Bit 4 enables more frequent conver-
sions on channel 1, as described in the
ADC
Conversion Sequence
section. Bit 3 enables resistance
cancellation on channel 1. See the
Series Resistance
Cancellation
section for more details. The remaining
bits of the configuration 1 register are not used. The
POR state of this register is 0000 0000 (00h).
Configuration 2 Register
The configuration 2 register functions are described in
Table 5. Bits [6:0] are used to mask the ALERT interrupt
output. Bit 6 masks the local alert interrupt and bits 5
through bit 0 mask the remote alert interrupts. The
power-up state of this register is 0000 0000 (00h).
Configuration 3 Register
Table 6 describes the configuration 3 register. Bits 5, 4,
3, and 0 mask the OVERT interrupt output for channels
6, 5, 4, and 1. The remaining bits, 7, 6, 2, and 1, are
reserved. The power-up state of this register is 0000
0000 (00h).
Status Register Functions
Status registers 1, 2, and 3 (Tables 7, 8, and 9) indicate
which (if any) temperature thresholds have been
exceeded and if there is an open-circuit or short-circuit
fault detected with the external sense junctions. Status
register 1 indicates if the measured temperature has
exceeded the threshold limit set in the ALERT registers
for the local or remote-sensing diodes. Status register 2
indicates if the measured temperature has exceeded
the threshold limit set in the OVERT registers. Status
register 3 indicates if there is a diode fault (open or
short) in any of the remote-sensing channels.
Bits in the alert status register clear by a successful
read, but set again after the next conversion unless the
fault is corrected, either by a drop in the measured tem-
perature or an increase in the threshold temperature.
The ALERT interrupt output follows the status flag bit.
Once the ALERT output is asserted, it can be deassert-
ed by either reading status register 1 or by successful-
ly responding to an alert response address. In both
7-Channel Precision Temperature Monitor
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