ADT7461

Reading the status register will clear the five flags, Bits 6–2,

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 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 0×21. The THERM

output will be reset only when the temperature falls to limit

value–hysteresis value.

When Pin 6 is configured as THERM2, only the high tempera-

ture limits are relevant. If Flag 6 and/or Flag 4 are set, the

THERM2 output goes low to indicate that the temperature

measurements are outside the programmed limits. Flag 5 and

Flag 3 have no effect on THERM2. The behavior of THERM2 is

otherwise the same as THERM.

Table 9. Status Register Bit Assignments

Bit

Name

Function

7

BUSY

1 When ADC Converting

6

LHIGH*

1 When Local High Temperature Limit Tripped

5

LLOW*

1 When Local Low Temperature Limit Tripped

4

RHIGH*

1 When Remote High Temperature Limit Tripped

3

RLOW*

1 When Remote Low Temperature Limit Tripped

2

OPEN*

1 When Remote Sensor Open Circuit

1

RTHRM

1 When Remote THERM Limit Tripped

0

LTHRM

1 When Local THERM Limit Tripped

*These flags stay high until the status register is read, or they are reset by POR.

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 accu-

racy on this channel, these offsets must be removed.

The offset value is stored as a 10-bit, twos complement value in

Registers 0×11 (high byte) and 0×12 (low byte, left justified).

Only the upper 2 bits of register 0×12 are used. The MSB of

Register 0×11 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 or subtracted to the meas-

ured 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 10. Sample Offset Register Codes

Offset Value

0×11

0×12

−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 com-

parison cycle when the ADT7461 is in standby mode, after

which the device returns to standby. Writing to the one-shot

register address (0×0F) causes the ADT7461 to perform a con-

version and comparison on both the internal and the external

temperature channels. This is not a data register as such, and it

is the write operation to Address 0×0F that causes the one-shot

conversion. The data written to this address is irrelevant and is

not stored.

Consecutive ALERT Register

The value written to this register determines how many out-of-

limit measurements must occur before an ALERT is generated.

The default value is that one out-of-limit measurement gener-

ates an ALERT. The maximum value that can be chosen is 4.

The purpose of this register is to allow the user to perform

some filtering of the output. This is particularly useful at the

fastest three conversion rates, where no averaging takes place.

This register is at Address 0×22.

Table 11. Consecutive ALERT Register Bit

Register Value

Number of Out-of-Limit

Measurements Required

y××× 000×

1

y××× 001×

2

y××× 011×

3

y××× 111×

4

× = Don’t care bit.

y = SMBus timeout bit. Default = 0. See SMBus section for more information.

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