AD7705 datasheet(25/32 Pages) AD

25 / 32 page

AD7705/AD7706

–25–

REV. A

POWER-ON/RESET FOR AD7705

CONFIGURE & INITIALIZE

C/ P SERIAL PORT

WRITE TO COMMUNICATIONS REGISTER SELECTING

CHANNEL & SETTING UP NEXT OPERATION TO BE A

WRITE TO THE CLOCK REGISTER (20 HEX)

WRITE TO CLOCK REGISTER SETTING THE CLOCK

BITS IN ACCORDANCE WITH THE APPLIED MASTER

CLOCK SIGNAL AND SELECT UPDATE RATE FOR

SELECTED CHANNEL (0C HEX)

WRITE TO COMMUNICATIONS REGISTER SELECTING

CHANNEL & SETTING UP NEXT OPERATION TO BE A

WRITE TO THE SETUP REGISTER (10 HEX)

WRITE TO SETUP REGISTER CLEARING F SYNC,

SETTING UP GAIN, OPERATING CONDITIONS &

INITIATING A SELF-CALIBRATION ON SELECTED

CHANNEL (40 HEX)

POLL

DRDY PIN

YES

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A READ FROM THE DATA

READ FROM DATA REGISTER

WRITE TO COMMUNICATIONS REGISTER SETTING UP NEXT

OPERATION TO BE A READ FROM THE COMMUNICATIONS

READ FROM COMMUNICATIONS REGISTER

POLL

DRDY BIT OF COMMUNICATIONS REGISTER

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A READ FROM THE DATA

START

READ FROM DATA REGISTER

DRDY

LOW?

YES

DRDY

LOW?

Figure 18. Flowchart for Setting Up and Reading from the AD7705

CONFIGURING THE AD7705/AD7706

The AD7705/AD7706 contains six on-chip registers that the

user can accesses via the serial interface. Communication with

any of these registers is initiated by writing to the Communica-

tions Register first. Figure 18 outlines a flow diagram of the

sequence used to configure all registers after a power-up or reset

on the AD7705, similar procedures apply to the AD7706. The

flowchart also shows two different read options—the first where

the

DRDY pin is polled to determine when an update of the

data register has taken place, the second where the

DRDY bit of

the Communications Register is interrogated to see if a data

gram is a series of words that should be written to the registers

for a particular set of operating conditions. These conditions

are gain of one, no filter sync, bipolar mode, buffer off, clock of

4.9512 MHz and an output rate of 50 Hz.

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