EVAL-ADM1026EB datasheet(27/56 Pages) AD

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ADM1026

Rev. A | Page 27 of 56

Chassis Intrusion Input

The chassis intrusion input is an active high input intended for

detection and signaling of unauthorized tampering with the

system. When this input goes high, the event is latched in Bit 6

of Status Register 4, and an interrupt is generated. The bit

remains set until cleared by writing a 1 to CI clear, Bit 1 of

Configuration Register 3 (05h), as long as battery voltage is

connected to the VBAT input. The CI clear bit itself is cleared by

writing a 0 to it.

The CI input detects chassis intrusion events even when the

ADM1026 is powered off (provided battery voltage is applied to

VBAT) but does not immediately generate an interrupt. Once a

chassis intrusion event is detected and latched, an interrupt is

generated when the system is powered on.

The actual detection of chassis intrusion is performed by an

external circuit that detects, for example, when the cover has

been removed. A wide variety of techniques may be used for the

detection, for example:

•

A microswitch that opens or closes when the cover is

removed.

•

A reed switch operated by magnet fixed to the cover.

•

A hall-effect switch operated by magnet fixed to the cover.

•

A phototransistor that detects light when the cover is

removed.

The chassis intrusion input can also be used for other types of

alarm input. Figure 49 shows a temperature alarm circuit using

an AD22105 temperature switch sensor. This produces a low-

going output when the preset temperature is exceeded, so the

output is inverted by Q1 to make it compatible with the CI

input. Q1 can be almost any small-signal NPN transistor, or a

TTL or CMOS inverter gate may be used if one is available.

See the AD22105 data sheet on the Analog Devices, Inc.

website (www.analog.com) for information on selecting RSET.

VCC

RSET

AD22105

TEMPERATURE

SENSOR

10k

Ω

Figure 49. Using the CI Input with a Temperature Sensor

General-Purpose I/O Pins (Open Drain)

The ADM1026 has eight pins that are dedicated to general-

purpose logic input/output (Pins 1, 2, and 43 to 48), eight pins

that can be configured as general-purpose logic pins or fan

speed inputs (Pins 3 to 6, and 9 to 12), and one pin that can

be configured as GPIO16 or the bidirectional THERM pin

(Pin 42). The GPIO/FAN pins are configured as general-

purpose logic pins by setting Bits 0 to 7 of Configuration

setting Bit 0 of Configuration Register 3, or as the THERM

function by clearing this bit.

Each GPIO pin has four data bits associated with it, two bits in

one of the GPIO configuration registers (Addresses 08h to 0Bh),

one in the GPIO status registers (Addresses 24h and 25h), and

one in the GPIO mask registers (Addresses 1Ch and 1Dh)

Setting a direction bit = 1 in one of the GPIO configuration

registers makes the corresponding GPIO pin an output.

Clearing the direction bit to 0 makes it an input.

Setting a polarity bit = 1 in one of the GPIO configuration

registers makes the corresponding GPIO pin active high.

Clearing the polarity bit to 0 makes it active low.

When a GPIO pin is configured as an input, the corresponding

bit in one of the GPIO status registers is read-only, and is set

when the input is asserted (“asserted” may be high or low

depending on the setting of the polarity bit).

When a GPIO pin is configured as an output, the corresponding

bit in one of the GPIO status registers becomes read/write.

Setting this bit then asserts the GPIO output. (Here again,

“asserted” may be high or low depending on the setting of the

polarity bit.)

The effect of a GPIO status register bit on the INT output can

be masked out by setting the corresponding bit in one of the

GPIO mask registers. When the pin is configured as an output,

this bit is automatically masked to prevent the data written to

the status bit from causing an interrupt, with the exception of

GPIO16, which must be masked manually by setting Bit 7 of

Mask Register 4 (Reg 1Bh).

When configured as inputs, the GPIO pins may be connected to

external interrupt sources such as temperature sensors with

digital output. Another application of the GPIO pins would be

to monitor a processor’s voltage ID code (VID code).

EVAL-ADM1026EB Datasheet(PDF) 27 Page - Analog Devices

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