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ADT7466
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to the
start bit (Bit 0) of Configuration Register 1 (0x00). The ADC
measures each analog input in turn, and, as each measurement
is completed, the result is automatically stored in the appropriate
value register. This round-robin monitoring cycle continues
until disabled by writing a 0 to Bit 0 of Configuration Register 1.
Rev. 0 | Page 21 of 48
Since the ADC is normally left to free-run in this manner, the
time to monitor all the analog inputs is normally not of interest,
because the most recently measured value of any input can be
read at any time.
For applications where the monitoring cycle time is important,
it can easily be calculated from the measurement times of the
individual channels. With averaging turned on, each
measurement is taken 16 times and the averaged result is placed
in the value register. The worst-case monitoring cycle times for
averaging turned on and off is described in Table 15.
Fan tach measurements are made in parallel but independently
and are not synchronized with the analog measurements.
Table 15. Monitoring Cycle Time
Monitoring Cycle Time
Avg On
8.99 ms
36.69 ms
36.69 ms
8.65 ms
8.65 ms
8.26ms
71.24 ms
90.63 ms
Channel
Local temperature
Remote 1 temperature
Remote 2 temperature
AIN1/Thermistor 1
AIN2/Thermistor 2
V
CC
Total
1
Total
2
1
Pin 11 and Pin 12 configured for AIN/thermistor monitoring. The total
excludes the Remote 2 temperature time.
2
Pin 11 and Pin 12 configured for second thermal diode monitoring. The total
excludes the AIN1/Thermistor 1 and AIN2/Thermistor 2 times.
ADDITIONAL ADC FUNCTIONS
A number of other functions are available on the ADT7466 to
offer the systems designer increased flexibility.
Avg Off
1.36 ms
6.25 ms
6.25 ms
1.02 ms
1.02 ms
0.61ms
10.26ms
14.47 ms
Turn Off Averaging
For each temperature measurement read from a value register,
16 readings have actually been made internally and the results
averaged before being placed into the value register. The user
may want to take a very fast measurement, for example, of CPU
temperature. Setting Bit 4 of Configuration Register 2 (0x01)
turns averaging off.
Single-Channel ADC Conversions
Setting Bit 3 of Configuration Register 4 (Address 0x03) places
the ADT7466 into single-channel ADC conversion mode. In
this mode, the ADT7466 can be made to read a single
temperature channel only. The selected input is read every
1.4 ms. The appropriate ADC channel is selected by writing to
Bits 2:0 of Configuration Register 4 (Address 0x03).
Table 16. ADC Single-Channel Selection
Bits 2:0, Reg. 0x03
000
001
010
011
100
101
LIMIT VALUES
High and low limits are associated with each measurement
channel on the ADT7466. These limits can form the basis of
system status monitoring; a status bit can be set for any out-of-
limit condition and detected by polling the device. Alternatively,
ALERT interrupts can be generated to flag out-of-limit
conditions for a processor or microcontroller.
Channel Selected
AIN1/ Thermistor1
AIN2/ Thermistor2
V
CC
Remote 1 temperature
Local temperature
Remote 2 temperature
Voltage and temperature limits are only 8-bit values and are
compared with the 8 MSBs of the voltage and temperature
values.
8-Bit Limits
The following tables list the 8-bit limits on the voltage limit and
temperature limit registers of the ADT7466.
Table 17. Voltage Limit Registers
Register
Description
0x14
AIN1 low limit
0x15
AIN1 high limit
0x16
AIN2 low limit
0x17
AIN2 high limit
0x18
V
CC
low limit
0x19
V
CC
high limit
Table 18. Temperature Limit Registers
Register
Description
0x1A
Remote temperature low limit
0x1B
Remote temperature high limit
0x1C
Local temperature low limit
0x1D
Local temperature high limit
0x1E
PROCHOT limit
0x1F
AIN1(TH1)/REM2 THERM limit
0x20
AIN2(TH2) THERM limit
0x21
Remote THERM limit
0x22
Local THERM limit
Default
0x00
0xFF
0x00
0xFF
0x00
0xFF
Default
0x00
0x7F
0x00
0x7F
0x00
0x64
0x64
0x64
0x64