ADT7481
http://onsemi.com
11
Table 13. 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 NORd
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.
" 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癈, and the maximum
is +127.75癈. 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癈
and will have no effect unless the user writes a different
value to it.
Table 14. SAMPLE OFFSET REGISTER CODES
Offset Value
0x11/0x34
0x12/0x35
128癈
1000 0000
00 00 0000
4癈
1111 1100
00 00 0000
1癈
1111 1111
00 000000
0.25癈
1111 1111
10 00 0000
0癈
0000 0000
00 00 0000
+0.25癈
0000 0000
01 00 0000
+1癈
0000 0001
00 00 0000
+4癈
0000 0100
00 00 0000
+127.75癈
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.