ADT7481
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10
Table 6. Conversion Rate/Channel Selector Register (Read Address 0x04, Write Address 0x0A)
Bit Mnemonic Function
7 Averaging Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion
rates (averaging cannot take place at the three faster rates, so setting this bit has no effect). When
default = 0, averaging is enabled.
6 Reserved Reserved for future use. Do not write to this bit.
<5:4> Channel Selector These bits are used to select the temperature measurement channels:
00 = Round robin = default = all channels measured
01 = Local temperature only measured
10 = Remote 1 temperature only measured
11 = Remote 2 temperature only measured
<3:0> Conversion Rates These bits set how often the ADT7481 measures each temperature channel.
Conversion rates are as follows:
Conversions/sec Time (seconds)
0000 = 0.0625
0001 = 0.125
0010 = 0.25
0011 = 0.5
0100 = 1
0101 = 2
0110 = 4
0111 = 8 = default
1000 = 16
1001 = 32
1010 = 64
1011 = continuous measurements
16
8
4
2
1
500 m
250 m
125 m
62.5 m
31.25 m
15.5 m
73 m (averaging enabled)
Limit Registers
The ADT7481 has three limits for each temperature
channel: high, low, and THERM
temperature limits for
local, Remote 1, and Remote 2 temperature measurements.
The remote temperature high and low limits span two
registers each to contain an upper and lower byte for each
limit. There is also a THERM
hysteresis register. All limit
registers can be written to, and read back from, the SMBus.
See Table 11 for details of the limit register addresses and
power−on default values.
C will result in an out−of−limit condition, setting a flag in
the status register.
If the low limit register is programmed with 0°C,
measuring 0°C or lower will result in an out−of−limit
condition.
Exceeding either the local or remote THERM
limit asserts
THERM
low. When Pin 8 is configured as THERM2,
exceeding either the local or remote high limit asserts
THERM2
low. A default hysteresis value of 10°C is
provided that applies to both THERM
channels. This
hysteresis value may be reprogrammed.
It is important to remember that the temperature limits
data format is the same as the temperature measurement data
format. So if the temperature measurement uses the default
binary scale, then the temperature limits also use the binary
scale. If the temperature measurement scale is switched,
however, the temperature limits do not automatically
switch.
The user must reprogram the limit registers to the desired
value in the correct data format. For example, if the remote
low limit is set at 10°C and the default binary scale is being
used, the limit register value should be 0000 1010b. If the
scale is switched to offset binary, the value in the low
temperature limit register should be reprogrammed to be
0100 1010b.
Status Registers
The status registers are read−only registers, at Address
0x02 (Status Register 1) and Address 0x23 (Status
Register 2). They contain status information for the
ADT7481.
Table 7. Status Register 1 Bit Assignments
Bit Mnemonic Function ALERT
7 BUSY 1 when ADC converting No
6
LHIGH
(Note 1)
1 when local high
temperature limit tripped
Yes
5
LLOW
(Note 1)
1 when local low
temperature limit tripped
Yes
4 R1HIGH
1
1 When Remote 1 High
Temperature Limit Tripped
Yes
3
R1LOW
(Note 1)
1 When Remote 1 Low
Temperature Limit Tripped
Yes
2
D1 OPEN
(Note 1)
1 When Remote 1 Sensor
Open Circuit
Yes
1 R1THRM1 1 when Remote1 THERM
Limit Tripped
No
0 LTHRM1 1 when local THERM Limit
Tripped
No
1. These flags stay high until the status register is read, or they
are reset by POR.
