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ADT7481ARMZ-1R7 Dual Channel Temperature Sensor and Overtemperature Alarm
Prototype PCB
Part No.:   ADT7481ARMZ-1R7
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Description:   Dual Channel Temperature Sensor and Overtemperature Alarm
File Size :   253 K    
Page : 20 Pages
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ADT7481
Table 8. Status Register 2 Bit Assignments
Bit
7
6
5
4
3
2
1
0
Mnemonic
Res
Res
Res
R2HIGH
(Note 1)
R2LOW
(Note 1)
D2 OPEN
(Note 1)
R2THRM1
ALERT
Function
Reserved for Future Use
Reserved for Future Use
Reserved for Future Use
1 When Remote 2 High
Temperature Limit Tripped
1 When Remote 2 Low
Temperature Limit Tripped
1 When Remote 2 Sensor
Open Circuit
1 When Remote 2
THERM Limit Tripped
1 When ALERT Condition
Exists
ALERT
No
No
No
Yes
Yes
Yes
No
No
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
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
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.
The Remote 1 offset MSBs are stored in Register 0x11
and the LSBs are stored in Register 0x12 (low byte, left
justified).
The Remote 2 offset MSBs are stored in Register 0x34
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
−128°C
−4°C
−1°C
−0.25°C
0°C
+0.25°C
+1°C
+4°C
+127.75°C
0x11/0x34
1000 0000
1111 1100
1111 1111
1111 1111
0000 0000
0000 0000
0000 0001
0000 0100
0111 1111
0x12/0x35
00 00 0000
00 00 0000
00 000000
10 00 0000
00 00 0000
01 00 0000
00 00 0000
00 00 0000
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.
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