Alarm Threshold Registers

Four registers store ALERT threshold values—one high-

register each for the local and remote channels. If

either measured temperature equals or exceeds the

corresponding ALERT threshold value, the ALERT out-

put is asserted.

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

An 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

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).

______________________________________________________________________________________

11

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

0 111 1111

127.00

0 111 1111

0 111 1111

126.00

0 111 1111

0 111 1111

25

0 001 1001

0 001 1001

0.00

0 000 0000

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

1 000 0000

Table 2. Data Format (Two's Complement)

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

Sensors with Overtemperature Alarms