Rainbow-electronics MAX6681 Manual de usuario descargar pdf (Pagina 13)

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.

When autoconverting, if the T

HIGH

and T

LOW

limits are

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

MAX6680/MAX6681

±1°C Fail-Safe Remote/Local Temperature

Sensors with SMBus Interface

______________________________________________________________________________________ 13

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

1 2 ... 8 9 10 11 12 13 14 15 16 17

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