AD7709 datasheet(19/32 Pages) AD

19 / 32 page

REV. A

AD7709

–19–

CONFIGURING THE AD7709

The four user-accessible registers on the AD7709 are accessed via

the serial interface. Communication with any of these registers

is initiated by first writing to the Communications Register. The

AD7709 begins converting on power-up without the need to

write to the registers. The default conditions are used, i.e., the

AD7709 operates at a 19.79 Hz update rate that offers 50 Hz

and 60 Hz rejection.

Figure 10 outlines a flow diagram of the sequence used to

configure all registers after a power-up or reset on the AD7709.

The flowchart shows two methods of determining when it is valid

to read the data register. The first method is hardware polling of

the

RDY pin and the second method involves software interrogation

of the RDY bit in the status register. The flowchart details all the

necessary programming steps required to initialize the ADC and

read data from the ADC channel following a power-on or reset.

The steps can be broken down as follows:

1. Configure and initialize the microcontroller or microproces-

sor serial port.

2. Initialize the AD7709 by configuring the following registers:

a) Filter Register to configure the update rate for the channel.

The AD7709 must be placed in standby mode before the

Filter Register can be written to.

b)Configuration Register to select the input channel to be

converted, its input range, and reference. This register is also

used to configure internal current sources, power switches,

and I/O port.

Both of these operations consist of a write to the Communi-

cations Register to specify the next operation as a write to a

specified register. Data is then written to this register. When

each sequence is complete, the ADC defaults to waiting for

another write to the Communications Register to specify the

next operation.

3. When configuration is complete, the user needs to determine

when it is valid to read the data from the data register. This is

accomplished either by polling the

RDY pin (hardware polling)

or by interrogating the RDY bit in the STATUS register

(software polling). Both are shown in Figure 10.

POLL

RDY PIN

HARDWARE

POLLING

START

SOFTWARE

POLLING

POWER-ON-RESET FOR AD7709

CONFIGURE AND INITIALIZE

C/ P SERIAL PORT