ADT7466 datasheet(21/48 Pages) AD

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ADT7466

Rev. 0 | Page 21 of 48

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.

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

Channel

Avg On

Avg Off

Local temperature

Remote 1 temperature

Remote 2 temperature

AIN1/Thermistor 1

AIN2/Thermistor 2

VCC

8.99 ms

36.69 ms

8.65 ms

8.26ms

1.36 ms

6.25 ms

1.02 ms

0.61ms

Total1

71.24 ms

10.26ms

Total2

90.63 ms

14.47 ms

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.

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

Channel Selected

000

AIN1/ Thermistor1

001

AIN2/ Thermistor2

010

VCC

011

Remote 1 temperature

100

Local temperature

101

Remote 2 temperature

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.

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

Description

Default

0x14

AIN1 low limit

0x00

0x15

AIN1 high limit

0xFF

0x16

AIN2 low limit

0x00

0x17

AIN2 high limit

0xFF

0x18

VCC low limit

0x00

0x19

VCC high limit

0xFF

Table 18. Temperature Limit Registers

Description

Default

0x1A

Remote temperature low limit

0x00

0x1B

Remote temperature high limit

0x7F

0x1C

Local temperature low limit

0x00

0x1D

Local temperature high limit

0x7F

0x1E

PROCHOT limit

0x00

0x1F

AIN1(TH1)/REM2 THERM limit

0x64

0x20

AIN2(TH2) THERM limit

0x64

0x21

Remote THERM limit

0x64

0x22

Local THERM limit

0x64

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