still exists, they are reasserted at the end of the next

conversion. If the MAX6680/MAX6681 are operating in

the comparator mode, bits 2–6 of the Status register

are cleared only after the local and/or remote tempera-

tures return within the set limits.

The bits indicating OVTI and OVTE are cleared only

when the condition no longer exists. Reading the status

byte does not clear the

OVERT output or fault bits. One

way to eliminate the fault condition is for the measured

temperature to drop below the temperature threshold

minus the hysteresis value. Another way to eliminate

the fault condition is by writing new values for the

RWOI, RWOE, or HYST registers so that a fault condi-

tion is no longer present.

The MAX6680/MAX6681 incorporate collision avoid-

ance so that completely asynchronous operation is

allowed between SMBus operations and temperature

conversions.

close together, it is possible for both high-temp and

low-temp status bits to be set, depending on the

amount of time between status read operations. In

these circumstances, it is best not to rely on the status

bits to indicate reversals in long-term temperature

changes. Instead use a current temperature reading to

establish the trend direction.

Hardware/Software Reset

The MAX6680/MAX6681 reset at power-on if pin 7 is

taken high, or by software reset through bit 1 of the

Configuration register. When reset occurs, all registers

go to default values, and the SMBus address pins are

sampled.

Conversion Rate Byte

The Conversion Rate register (Table 8) programs the

time interval between conversions in free-running

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

______________________________________________________________________________________

13

REGISTER

ADDRESS

POR STATE

FUNCTION

RLTS

00h

0000

at 0°C

Read Internal Temperature

RRTE

01h

0000

(0°C)

Read External Temperature

RSL

02h

0000 0000

Read Status Register

RCL/WCL

03h/09h

0010 0000

Read/Write Configuration Byte

RCRA/WCRA

04h/0A

0000 0010

Read/Write Conversion Rate Byte

RIH/WIH

05h/0Bh

0111 1111

(+127°C)

Read/Write Internal

ALERT High Limit

RIL/WIL

06h/0Ch

1100 1001

( -55°C)

Read/Write Internal

ALERT Low Limit

REH/WEH

07h/0Dh

0100 0110

(+127°C)

Read/Write External

ALERT High Limit

REL/WEL

08h/0Eh

1100 1001

(-55°C)

Read/Write External

ALERT Low Limit

OSHT

0Fh

0000

One Shot

REET

10h

0000 0000

Read External Extended Temperature

RWOH

11h

0000 0000

Read/Write External Offset High Byte

RWOL

12h

0000 0000

Read/Write External Offset Low Byte

RWOE

19h

See Table 4

Read/Write External

OVERT Limit

RWOI

20h

See Table 4

Read/Write Internal

OVERT Limit

HYST

21h

0000 0110

(+6°C)

OVERT Hysteresis

RDID

FEh

0100 1101

Read Manufacturer ID

RDRV

Ff

0000 0001

Read Device Revision

Table 5. Command-Byte Register Bit Assignments