AD7294 datasheet(38/45 Pages) AD

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AD7294

Preliminary Technical Data

Rev. PrB | Page 38 of 45

MODES OF OPERATION

When supplies are first applied to the AD7294 the ADC powers

up in sleep mode and normally rmains in this shutdown state

while not converting. There are two different methods of

initiating a conversion on the AD7294.

MODE 1 – COMMAND MODE

In this mode the part cycles through the selected channels on

each subsequent read. To setup the command mode the

command register must first be told which ADC channels to

convert on, see Table 7 . In the case of TSENSE1, TSENSE2 and

TSENSEINT, the command mode is not actually requesting a

conversion but outputting the last automatic conversion in

sequence. In the case of the internal temperature sensor

TSENSEINT, it is not possible to read the result via the ADC result

Figure 35 illustrates a 2–byte read operation from the result

pointer is pointing to the command register. In the command

point the ADC will power up and begin channel conversions.

Also take note that the address pointer must be re-addressed to

the result register to read the conversions results. For each

channel conversion in the sequence, the frame is re-addressed

to the result register to synchronize the frames. When more

then one channel is selected in the command register. The first

read accesses the data from the conversion on channel1. While

this read takes place, a conversion occurs on channel 2. The

second read accesses this data from channel 2 and so on.

The wake-up and conversion time together should take

approximately 5 μs, and the conversion begins when the last bit

in the command register has been clocked in.

SD A

ACK. B Y

AD7294

R/W

SC L

C 6

FR A ME 3

C OMMAND REGISTER VALUE

SC L (CON TIN U ED )

SD A (CO NTINUE D)

ST AR T BY

MA ST ER

ACK. BY

AD7294

A CK. BY

AD7294

FR A ME 1

SERIAL BUS A DDR E SS BYT E + WRITE

FRAME 2

COMMAND PO IN TER RE GIST ER BY TE

ACK. B Y

AD7294

FR A ME 4

POINTER TO RESULT REGISTER

SC L (CON TIN U ED )

SD A (CO NTINUE D)

R/W

A CK. BY

AD7294

FR A ME 5

SERIAL BUS ADDRESS BYTE + READ

REPEATED START

BY MASTER

ACK. BY

MASTER

ALERT CHID

D10

D11

FR A ME 6

MOST SIGNIFICANT DATA BYTE

SC L (CON TIN U ED )

SD A (CONTINUE D)

NO ACK BY

MASTER

FR A ME 7

LEAST SIGNIFICANT DATA BYTE

CHID

STOP BY

MASTER

Figure 35. Command Mode Operation

AD7294 Datasheet(PDF) 38 Page - Analog Devices

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