AD7992 datasheet(18/21 Pages) AD

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AD7992

–18–

REV. PrH

PRELIMINARYTECHNICAL DATA

Figure 14. Reading two bytes of data from the Conversion

Result Register

Figure 13. Reading a single byte of data from a selected

SMBus ALERT to signal the host device that it wants to

talk. The SMBus ALERT on the AD7992 is used as an

out of conversion range indicator.

The ALERT pin has an open-drain configuration which

allows the ALERT outputs of several AD7992 devices to

be wired-AND together when the ALERT pin is active

low. D0 of the Configuration Register is used to set the

active polarity of the ALERT output. The power-up de-

fault is active low. The ALERT function can be disabled

or enabled by setting D2 of the Configuration Register to

1 or 0 respectively.

The host device can process the ALERT interrupt and

simultaneously access all SMBus ALERT devices through

the alert response address. Only the device which pulled

the ALERT low will acknowledge the ARA (Alert Re-

sponse Address). If more than one device pulls the

ALERT pin low, the highest priority (lowest address)

device will win communication rights via standard I2C

arbitration during the slave address transfer.

The ALERT output becomes active when the value in the

Conversion Result Register exceeds the value in the

DATAHIGH Register or falls below the value in the

DATALOW Register . It is reset when a write operation to

the Configuration register sets D1 to a 1, or when the

conversion result returns N LSBs below or above the value

stored in the DATAHIGH Register or DATALOW Register

respectively. N is the value in the Hysteresis register. (See

Limit Registers section)

The ALERT output requires an external pull-up resistor.

This can be connected to a voltage different from VDD

provided the maximum voltage rating of the ALERT out-

put pin is not exceeded. The value of the pull-up resistor

depends on the application, but should be as large as pos-

sible to avoid excessive sink currents at the ALERT out-

put.

SDA

NO ACK. BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

SINGLE DATA BYTE FROM AD7992

ACK. BY

AD7992

SCL

STOP BY

MASTER

SDA

ACK. BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

MOST SIGNIFICANT DATA BYTE FROM AD7992

ACK. BY

AD7992

Alert_

Flag

D10

SCL

D11

NO ACK. BY

MASTER

FRAME 3

LEAST SIGNIFICANT DATA BYTE FROM AD7992

STOP BY

MASTER

SCL (CONTINUED)

SDA (CONTINUED)

CH ID0

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