ADT7467ARQZ-R7 datasheet(21/77 Pages) ONSEMI

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ADT7467

Rev. 3 | Page 21 of 77 | www.onsemi.com

LIMITS, STATUS REGISTERS, AND INTERRUPTS

LIMIT VALUES

High and low limits are associated with each measurement

channel on the ADT7467. These limits form the basis of

system-status monitoring in that a status bit can be set for any

out-of-limit condition and detected by polling the device.

Alternatively, SMBALERT interrupts can be generated to flag a

processor or microcontroller of out-of-limit conditions.

8-Bit Limits

The following is a list of 8-bit limits on the ADT7467.

Voltage Limit Registers

Temperature Limit Registers

default

THERM Limit Register

16-Bit Limits

The fan TACH measurements are 16-bit results. The fan TACH

limits are also 16 bits, consisting of a high byte and low byte.

Because slow or stalled fans are normally the only conditions of

interest, only high limits exist for fan TACHs. Because the fan

TACH period is measured, exceeding the limit indicates a slow

or stalled fan.

Fan Limit Registers

Out-of-Limit Comparisons

Once all limits are programmed, the ADT7467 can be enabled

for monitoring. The ADT7467 measures all voltage and

temperature measurements in round-robin format and sets

the appropriate status bit for out-of-limit conditions. TACH

measurements are not part of this round-robin cycle. Compari-

sons are done differently, depending on whether the measured

value is being compared to a high or low limit.

High limit: > comparison performed

Low limit: ≤ comparison performed

Voltage and temperature channels use a window comparator for

error detecting and, therefore, have high and low limits. Fan

speed measurements use only a low limit. This fan limit is

needed only in manual fan control mode.

Analog Monitoring Cycle Time

The analog monitoring cycle begins when a 1 is written to the

start bit (Bit 0) of Configuration Register 1 (0x40). By default,

the ADT7463 powers up with this bit set. The ADC measures

each analog input in turn and, as each measurement is com-

pleted, the result is automatically stored in the appropriate value

disabled by writing a 0 to Bit 0 of Configuration Register 1.

As the ADC is normally left to free-run in this manner, the time

to monitor all analog inputs is normally not of interest because the

most recently measured value of an input can be read at any time.

For applications where the monitoring cycle time is important,

it can be calculated easily. The total number of channels

measured is

•

One dedicated supply voltage input (VCCP)

•

One supply voltage (VCC pin)

•

One local temperature

•

Two remote temperatures

As mentioned previously, the ADC performs round-robin

conversions. The total monitoring cycle time for averaged

voltage and temperature monitoring is 145 ms. The total

monitoring cycle time for voltage and temperature monitoring

with averaging disabled is 19 ms. The ADT7467 is a derivative

of the ADT7468. As a result, the total conversion time for the

ADT7467 and ADT7468 are the same, even though the

ADT7467 has less monitored channels.

ADT7467ARQZ-R7 Datasheet(PDF) 21 Page - ON Semiconductor

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