ADT7476AARQZ-R datasheet(22/69 Pages) ONSEMI

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ADT7476A

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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 Interrupt

Status Register 1 and Interrupt Status Register 2. The status

measurement and limit comparison on that channel. If a

measurement is within limits, the corresponding status

the corresponding status register bit is set to 1.

The state of the various measurement channels can be

polled by reading the status registers over the serial bus. In

Bit 7 (OOL) of Interrupt Status Register 1 (0x41), 1 means

an out-of-limit event has been flagged in Interrupt Status

Status Register 2. Alternatively, Pin 10 or Pin 14 can be

configured as an SMBALERT output. This hard interrupt

automatically notifies 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 is set, indicating an out-of-limit

condition, it remains 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

registers (0x74 and 0x75) allow individual interrupt sources

to be masked from causing an SMBALERT. However, if one

of these masked interrupt sources goes out of limit, its

associated status bit is set in the status registers.

Table 28. INTERRUPT STATUS REGISTER 1 (0x41)

Bit

Mnemonic

Description

[7]

OOL

1 denotes a bit in Interrupt Status

[6]

R2T

1 indicates that the Remote 2

Temperature High or Low limit has been

exceeded.

[5]

1 indicates that the Local Temperature

High or Low Limit has been exceeded.

[4]

R1T

1 indicates that the Remote 1

Temperature High or Low Limit has

been exceeded.

[3]

5.0 V

1 indicates that the 5.0 V High or Low

Limit has been exceeded.

[2]

VCC

1 indicates that the VCC High or Low

Limit has been exceeded.

[1]

VCCP

1 indicates that the VCCP High or Low

Limit has been exceeded.

[0]

2.5 V

1 indicates that the 2.5 V High or Low

Limit has been exceeded.

If the 2.5 V input is configured as

THERM, this bit represents the status of

THERM.

Table 29. INTERRUPT STATUS REGISTER 2 (0x42)

Bit

Mnemonic

Description

[7]

1 indicates an open or short on

D2+/D2− inputs.

[6]

1 indicates an open or short on

D1+/D1− inputs.

[5]

F4P

1 indicates Fan 4 has dropped below

minimum speed. Alternatively, indicates

that the THERM limit has been

exceeded, if the THERM function is

used. Alternatively, indicates the status

of GPIO6.

[4]

FAN3

1 indicates that Fan 3 has dropped

below minimum speed.

[3]

FAN2

1 indicates that Fan 2 has dropped

below minimum speed.

[2]

FAN1

1 indicates that Fan 1 has dropped

below minimum speed.

[1]

OVT

1 indicates that a THERM

overtemperature limit has been

exceeded.

[0]

12 V/VC

1 indicates a 12 V high or low limit has

been exceeded. If the VID code change

function is used, this bit indicates a

change in VID code on the VID0 to

VID4 inputs.

SMBALERT Interrupt Behavior

The ADT7476A can be polled for status, or an

SMBALERT interrupt can be generated for out-of-limit

conditions. It is important to note how the SMBALERT

output and status bits behave when writing interrupt handler

software.

Figure 29. SMBALERT and Status Bit Behavior

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

CLEARED ON READ

(TEMP BELOW LIMIT)

TEMP BACK IN LIMIT

(STATUS BIT STAYS SET)

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

Figure 29 shows how the SMBALERT output and sticky

status bits behave. Once a limit is exceeded, the

corresponding status bit is set to 1. The status bit remains set

until the error condition subsides and the status register is

read. The status bits are referred to as sticky because they

remain set until read by software. This ensures that an

out-of-limit event cannot be missed if the software is

periodically polling the device.

ADT7476AARQZ-R Datasheet(PDF) 22 Page - ON Semiconductor

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