Table 3. extended resolution register, Table 2. data format (two's complement) – Rainbow Electronics MAX6659 User Manual

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Alarm Threshold Registers

Four registers store

ALERT threshold values—one high-

temperature (T

HIGH

) and one low-temperature (T

LOW

)

ALERT threshold value, the ALERT out-

put is asserted.

The POR state of both

ALERT T

HIGH

registers is 0100

0110 or +70°C and the POR state of T

LOW

registers is

1100 1001 or -55°C.

Four additional registers store remote and local alarm
threshold data corresponding to the

OVERT1 and

OVERT2 (MAX6659 only) outputs. The values stored in
these registers are high-temperature thresholds. If any
one of the measured temperatures equals or exceeds
the corresponding alarm threshold value, an

OVERT

output is asserted. The POR state of the

OVERT thresh-

old is 0101 0101 or +85°C.

Alert

Interrupts

ALERT interrupt occurs when the internal or external

temperature reading exceeds a high or low tempera-
ture limit (user programmed) or when the remote diode
is disconnected (for continuity fault detection). The

ALERT interrupt output signal is latched and can be
cleared only by either reading the Status register or by
successfully responding to an Alert Response address.
In both cases, the alert is cleared even if the fault con-
dition still exists, but is reasserted at the end of the next
conversion. The interrupt does not halt automatic con-
versions. The interrupt output pin is open-drain so that
multiple devices can share a common interrupt line.
The interrupt rate never exceeds the conversion rate.

Alert Response Address

The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that
lack the complex, expensive logic needed to be a bus
master. Upon receiving an ALERT interrupt signal, the
host master can broadcast a Receive Byte transmission
to the Alert Response slave address (0001100). Then,
any slave device that generated an interrupt attempts
to identify itself by putting its own address on the bus
(Table 8).

The Alert Response can activate several different slave
devices simultaneously, similar to the I

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
acknowledge 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.

OVERT

Overtemperature

Alarm/Warning Outputs

OVERT1 and OVERT2 (MAX6659 only) are asserted
when the temperature rises to a value programmed in
the appropriate threshold register. They are deasserted
when the temperature drops below this threshold minus
the hysteresis. An OVERT output can be used to acti-
vate a cooling fan, send a warning, or trigger a system
shutdown to prevent component damage. The HYST
byte sets the amount of hysteresis for both OVERT out-
puts. The data format for the HYST byte is the same for
the other temperature registers (Table 2).

MAX6657/MAX6658/MAX6659

______________________________________________________________________________________

FRACTIONAL

TEMPERATURE

CONTENTS OF

EXTENDED REGISTER

0.000

000X XXXX

0.125

001X XXXX

0.250

010X XXXX

0.375

011X XXXX

0.500

100X XXXX

0.625

101X XXXX

0.750

110X XXXX

0.875

111X XXXX

Table 3. Extended Resolution Register

Note: Extended resolution applies only for conversion rates of
4Hz and slower.

DIGITAL OUTPUT

TEMP (

°C)

MAX6657

MAX6658
MAX6659

130.00

0 111 1111

127.00

0 111 1111

126.00

0 111 1111

0 001 1001

0.00

0 000 0000

-1

1 000 0000

1 111 1111

-25

1 000 0000

1 110 0111

-55

1 000 0000

1 100 1001

Diode Fault

(Short or Open)

1 000 0000

Table 2. Data Format (Two's Complement)

±1°C, SMBus-Compatible Remote/Local Temperature

Sensors with Overtemperature Alarms