ADM1027 datasheet(18/56 Pages) AD

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REV. A

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ADM1027

ANALOG MONITORING CYCLE TIME

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

start bit (Bit 0) of Configuration Register 1(Reg. 0x40). The

ADC measures each analog input in turn and as each mea-

surement is completed, the result is automatically stored in the

appropriate value register. This round-robin monitoring cycle

continues unless disabled by writing a 0 to Bit 0 of Configura-

tion Register 1.

Since the ADC will normally be left to free-run in this manner,

the time taken to monitor all the analog inputs will normally not

be of interest as the most recently measured value of any input

can be read out at any time.

For applications where the monitoring cycle time is important,

it can easily be calculated.

The total number of channels measured is

∑ Four dedicated supply voltage inputs

∑ 3.3 VSTBY or 5 V supply (VCC pin)

∑ Local temperature

∑ Two remote temperatures

As mentioned previously, the ADC performs round-robin con-

versions and takes 11.38 ms for each voltage measurement,

12 ms for a local temperature reading, and 25.5 ms for a remote

temperature reading.

The total monitoring cycle time for averaged voltage and tem-

perature monitoring is therefore nominally

11.38) + 12 + (2

25.5) = 120 ms

Fan TACH measurements are made in parallel and are not

synchronized with the analog measurements in any way.

STATUS REGISTERS

The results of limit comparisons are stored in Status Registers 1

and 2. The status register bit for each channel reflects the status of

the last measurement and limit comparison on that channel.

If a measurement is within limits, the corresponding status

the corresponding status register bit will be set to 1.

The state of the various measurement channels may be polled by

reading the status registers over the serial bus. When 1, Bit 7

(OOL) of Status Register 1 (Reg. 0x41) means that an out-of-

limit event has been flagged in Status Register 2. This means that

the user need read only Status Register 2 when this bit is set.

Alternatively, Pin 10 can be configured as an

SMBALERT output.

This will automatically notify the system supervisor of an

out-of-limit condition. Reading the status registers clears the

appropriate status bit as long as the error condition that caused

the interrupt has cleared. Status register bits are “sticky.”

Whenever a status bit gets set, indicating an out-of-limit

condition, it will remain set even if the event that caused it has

gone away (until read). The only way to clear the status bit is to

read the status register after the event has gone away. Interrupt

status mask registers (Reg. 0x74, 0x75) allow individual inter-

rupt sources to be masked from causing an

SMBALERT.

However, if one of these masked interrupt sources goes out-

of-limit, its associated status bit will get set in the interrupt

status registers.

STATUS REGISTER 1 (REG. 0x41)

Bit 7 (OOL) = 1, denotes a bit in Status Register 2 is set and

Status Register 2 should be read.

Bit 6 (R2T) = 1, Remote 2 temp high or low limit has been

exceeded.

Bit 5 (LT) = 1, Local temp high or low limit has been exceeded.

Bit 4 (R1T) = 1, Remote 1 temp high or low limit has been

exceeded.

Bit 3 (5 V) = 1, 5 V high or low limit has been exceeded.

Bit 2 (VCC) = 1, VCC high or low limit has been exceeded.

Bit 1 (VCCP) = 1, VCCP high or low limit has been exceeded.

Bit 0 (2.5 V) = 1, 2.5 V high or low limit has been exceeded.

STATUS REGISTER 2 (REG. 0x42)

Bit 7 (D2) = 1, indicates an open or short on D2+/D2– inputs.

Bit 6 (D1) = 1, indicates an open or short on D2+/D2– inputs.

Bit 5 (FAN4) = 1, indicates Fan 4 has dropped below mini-

mum speed.

Bit 4 (FAN3) = 1, indicates Fan 3 has dropped below mini-

mum speed.

Bit 3 (FAN2) = 1, indicates Fan 2 has dropped below mini-

mum speed.

Bit 2 (FAN1) = 1, indicates Fan 1 has dropped below mini-

mum speed.

Bit 1 (OVT) = 1, indicates that a THERM overtemperature

limit has been exceeded.

Bit 0 (12 V) = 1, 12 V high or low limit has been exceeded.

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