ADT7481

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11

Table 8. Status Register 2 Bit Assignments

Bit

Mnemonic

Function

ALERT

7

Res

Reserved for Future Use

No

6

Res

Reserved for Future Use

No

5

Res

Reserved for Future Use

No

4

R2HIGH

(Note 1)

1 When Remote 2 High

Temperature Limit Tripped

Yes

3

R2LOW

(Note 1)

1 When Remote 2 Low

Temperature Limit Tripped

Yes

2

D2 OPEN

(Note 1)

1 When Remote 2 Sensor

Open Circuit

Yes

1

R2THRM1

1 When Remote 2

THERM Limit Tripped

No

0

ALERT

1 When ALERT Condition

Exists

No

1. These flags stay high until the status register is read, or they

are reset by POR.

The eight flags that can generate an ALERT are NOR’d

together. When any flag is high, the ALERT interrupt latch

is set and the ALERT output goes low (provided that the

flag(s) is/are not masked out).

Reading the Status 1 register will clear the five flags (Bit 6

through Bit 2) in Status Register 1, provided the error

conditions that caused the flags to be set have gone away.

Reading the Status 2 register will clear the three flags (Bit 4

through Bit 2) in Status Register 2, provided the error

conditions that caused the flags to be set have gone away. A

flag bit can only be reset if the corresponding value register

contains an in−limit measurement, or if the sensor is good.

The ALERT interrupt latch is not reset by reading the

status register. It will be reset when the ALERT output has

been serviced by the master reading the device address,

provided the error condition has gone away and the status

register flag bits have been reset.

When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1

of Status Register 2 are set, the THERM output goes low to

indicate that the temperature measurements are outside the

programmed limits. The THERM output does not need to be

reset, unlike the ALERT output. Once the measurements are

within the limits, the corresponding status register bits are

reset automatically, and the THERM output goes high. The

user may add hysteresis by programming Register 0x21. The

THERM output will be reset only when the temperature falls

below the THERM limit minus hysteresis.

When Pin 8 is configured as THERM2, only the high

temperature limits are relevant. If Flag 6 and Flag 4 of Status

Register 1, or Flag 4 of Status Register 2 are set, the

THERM2 output goes low to indicate that the temperature

measurements are outside the programmed limits. Flag 5

and Flag 3 of Status Register 1, and Flag 3 of Status

Register 2 have no effect on THERM2. The behavior of

THERM2 is otherwise the same as THERM.

Bit 0 of Status Register 2 gets set whenever the ALERT

output is asserted low. Thus, the user need only read Status

Register 2 to determine if the ADT7481 is responsible for

the ALERT. This bit gets reset when the ALERT output gets

reset. If the ALERT output is masked, then this bit is not set.

Offset Register

Offset errors may be introduced into the remote

temperature measurement by clock noise or by the thermal

diode being located away from the hot spot. To achieve the

specified accuracy on this channel, these offsets must be

removed.

The offset values are stored as 10−bit, twos complement

values.

and the LSBs are stored in Register 0x12 (low byte, left

justified).

and the LSBs are stored in Register 0x35 (low byte, left

justified). The Remote 2 offset can be written to, or

read from, the Remote 1 offset registers if Bit 3 of the

Configuration 1 register is set to 1. This bit should be

set to 0 (default) to read the Remote 1 offset values.

Only the upper two bits of the LSB registers are used. The

MSB of the MSB offset register is the sign bit. The minimum

offset that can be programmed is −128

°C, and the maximum

is +127.75

°C. The value in the offset register is added to, or

subtracted from, the measured value of the remote

temperature.

The offset register powers up with a default value of 0

°C

and will have no effect unless the user writes a different

value to it.

Table 9. Sample Offset Register Codes

Offset Value

0x11/0x34

0x12/0x35

−128°C

1000 0000

00 00 0000

−4°C

1111 1100

00 00 0000

−1°C

1111 1111

00 000000

−0.25°C

1111 1111

10 00 0000

0°C

0000 0000

00 00 0000

+0.25°C

0000 0000

01 00 0000

+1°C

0000 0001

00 00 0000

+4°C

0000 0100

00 00 0000

+127.75°C

0111 1111

11 00 0000

One−Shot Register

The one−shot register is used to initiate a conversion and

comparison cycle when the ADT7481 is in standby mode,

after which the device returns to standby. Writing to the

one−shot register address (0x0F) causes the ADT7481 to

perform a conversion and comparison on both the local and

the remote temperature channels. This is not a data register

as such, and it is the write operation to Address 0x0F that

causes the one−shot conversion. The data written to this

address is irrelevant and is not stored. However the ALERT

and THERM outputs are not operational in one−shot mode

and should not be used.