AD7709

–17–

REV. PrA

January 2001

PRELIMINARY TECHNICAL DATA

CONFIGURING THE AD7709

On the AD7709 there are only four user accessable registers and these are configured via the serial interface. Communica-

tion with any of these registers is initiated by firstly writing to the Communications Register. The AD7709 starts convert-

ing after a power up without the requiring any register to be written to. The defaults conditions are used and the AD7709

operates at a 20Hz update rate offering 50 and 60Hz rejection.

Figure 5 outlines a flow diagram of the sequence used to configure the registers on the AD7709 following a power-up.

The flowchart shows two methods of determining when its valid to read the data register. The first method is hardware

polling of the RDY pin and the second method involves software interrogation of bits in the status and mode registers. The

flowchart details all the necessary programming steps required to initialize the ADC and read data from the selected ADC chan-

nel following a power-on or reset.The steps can be broken down as follows:

1. Configure and initialize the microcontroller or microprocessor serial port.

2. Initialize the AD7709 by configuring the following registers:

a)FILTER registers which determines the update rate. The AD7709 must be put into standby mode before writing to the

filter register.

b) CONFIGURATION register to select the input channel to be converted, its input range and reference. This register is

also used to configure the internal current sources, power switches and I/O port.

Both of these operations consist of a write to the communications 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 its valid to read the data from the data register. This

is accomplished by either polling the RDY pin (hardware polling) or by interrogating the bits in the STATUS register

(software polling). Both are shown in the following flowchart.

HARDWARE

POLLING

SOFTWARE

POLLING

POWER-ON/RESET FOR AD7709

CONFIGURE & INITIALIZE

C/ P SERIAL PORT

WRITE TO COMMUNICATIONS REGISTER SELECTING

NEXT OPERATION TO BE A WRITE TO

THE FILTER REGISTER (WRITE 22HEX TO COMMS REG)

WRITE TO FILTER REGISTER TO CONFIGURE

THE REQUIRED UPDATE RATE.

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A WRITE TO THE

CONFIGURATION REGISTER (WRITE 01Hex TO COMMS REG)

START

WRITE TO CONFIGURATION REGISTER TO SELECT INPUT

CHANNEL, INPUT RANGE AND REFERENCE. CURRENT

SOURCES AND I/O PORT CAN ALSO BE CONFIGURED

WRITE TO COMMUNICATIONS REGISTER SETTING UP NEXT

OPERATION TO BE A READ FROM THE STATUS REGISTER

WRITE 40HEX TO COMMS REGISTER

READ STATUS REGISTER

NO

YES

RDY=1

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A READ OF THE DATA

REGISTER. WRITE 43HEX TO COMMS REGISTER

SOFTWARE POLLING

POLL

RDY PIN

NO

RDY

LOW?

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A READ OF THE

DATA REGISTER (WRITE 43HEX TO COMMS REGISTER)

READ16-BIT DATA RESULT

YES

ANOTHER

READ?

NO

CHANNEL

CHANGE

NO

YES

END

HARDWARE POLLING

READ DATA FROM OUTPUT REGISTER

READ16-BIT DATA RESULT

YES

ANOTHER

READ?

NO

CHANNEL

CHANGE

NO

YES

END

Figure 5. Flowchart for Configuring and reading from AD7709