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 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.
• 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 14. 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.
