MAX6695/MAX6696
The POR state of both internal and external ALERT low-
temperature limit registers is 1100 1001 or -55°C. Use
bit 3 of the configuration register to select remote 1 or
remote 2 when reading or writing remote thresholds.
Additional registers, RWO1E, RWO1I, RWO2E, and
RWO2I, store remote and local alarm threshold data
information corresponding to the OT1 and OT2 outputs
(See the
OT1 and OT2 Overtemperature Alarms
section.)
ALERT
Interrupt Mode
An ALERT interrupt occurs when the internal or external
temperature reading exceeds a high- or low-tempera-
ture limit (both limits are user programmable), or when
the remote diode is disconnected (for continuity fault
detection). The ALERT interrupt output signal is latched
and can be cleared only by reading either of the status
registers or by successfully responding to an Alert
Response address. In both cases, the alert is cleared
but is reasserted at the end of the next conversion if the
fault condition still exists. The interrupt does not halt
automatic conversions. The interrupt output pin is open
drain so that multiple devices can share a common
interrupt line. The interrupt rate never exceeds the con-
version rate.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices. Upon
receiving an interrupt signal, the host master can
broadcast a Receive Byte transmission to the Alert
Response slave address (see
Slave Addresses
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
acknowledgement 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 interrupt latch, provided the condition that
caused the alert no longer exists. If the condition still
exists, the device reasserts the ALERT interrupt at the
end of the next conversion.
OT1
and
OT2
Overtemperature Alarms
Two registers, RWO1E and RWO1I, store remote and
local alarm threshold data corresponding to the OT1
output. Two other registers, RWO2E and RWO2I, store
remote and local alarm threshold data corresponding
to the OT2 output. The values stored in these registers
are high-temperature thresholds. The OT1 or OT2 out-
put is asserted if any one of the measured tempera-
tures equals or exceeds the corresponding alarm
threshold value.
OT1 and OT2 always operate in comparator mode and
are asserted when the temperature rises above a value
programmed in the appropriate threshold register. They
are deasserted when the temperature drops below this
threshold, minus the programmed value in the hystere-
sis HYST register (21h). An overtemperature output can
be used to activate a cooling fan, send a warning, initi-
ate clock throttling, or trigger a system shutdown to
prevent component damage. The HYST byte sets the
amount of hysteresis to deassert both OT1 and OT2
outputs. The data format for the HYST byte is 7 bit +
sign with +1°C resolution. Bit 7 of the HYST register
should always be zero.
OT1 responds immediately to temperature faults. OT2
activates either immediately or after four consecu-
tive remote channel temperature faults, depending on
the state of the fault queue bit (bit 5 of the configura-
tion register).
Command Byte Functions
The 8-bit command byte register (Table 5) is the master
index that points to the various other registers within the
MAX6695/MAX6696. This register’s POR state is 0000
0000, so a Receive Byte transmission (a protocol that
lacks the command byte) occurring immediately after
POR returns the current local temperature data.
One-Shot
The one-shot command immediately forces a new con-
version cycle to begin. If the one-shot command is
received when the MAX6695/MAX6696 are in software
standby mode (RUN/STOP bit = 1), a new conversion is
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
12 ______________________________________________________________________________________
