AD7731

–36–

REV. 0

CONFIGURING THE AD7731

The AD7731 contains twelve on-chip registers which can be accessed via the serial interface. Figure 5 and Figure 6 have outlined a

flowchart for the reading and writing of these registers. Table XIX and Table XX outline sample pseudo-code for some commonly

used routines. The required operating conditions will dictate the values loaded to the Mode and Filter Registers. The values given

here are for example purposes only.

Table XIX. Pseudo-Code for Initiating a Self-Calibration after Power-On/Reset

Write 03 Hex to Serial Port

1

/* Writes to Communications Register Setting Next Operation as Write to

Filter Register*/

Write 1332 Hex to Serial Port

1

/* Writes to Filter Register Setting a 1 kHz Output Rate in nonCHOP

Mode*/

Write 02 Hex to Serial Port

/* Writes to Communications Register Setting Next Operation as Write to

Mode Register*/

Write B174 Hex to Serial Port

/* Writes to Mode Register Initiating Internal Full-Scale Calibration for

0 V to +1.28 V Input Range on Channel Pair AIN1/AIN2*/

Wait for

RDY Low

/* Wait for

RDY pin to go low to indicate end of calibration cycle*/

Write 02 Hex to Serial Port

/* Writes to Communications Register Setting Next Operation as Write to

Mode Register*/

Write 9174 Hex to Serial Port

/* Writes to Mode Register Initiating Internal Zero-Scale Calibration for

0 V to +1.28 V Input Range*/

Wait for

RDY Low

/* Wait for

RDY pin to go low to indicate end of calibration cycle*/

/* The part has now completed self-calibration and is in idle mode*/

Table XX. Pseudo-Code for Looping AD7731 Through Three Fully-Differential Channels

CHANNEL = 4 Hex

/* Sets a Variable Called CHANNEL*/

CH_LOOP: MODE = 2177 Hex

/* Sets a Variable Called MODE */

MODE = MODE AND CHANNEL

/* Logical AND of Both Variables */

Write 02 Hex to Serial Port

/* Writes to Communications Register Setting Next Operation as Write to

Mode Register*/

Write MODE to Serial Port

/* Writes to Mode Register Setting Continuous Conversion Mode for 0 V

to +1.28 V Input Range on Channel Determined by CHANNEL Variable*/

Wait for

RDY Low

/* Wait for

RDY pin to go low to Indicate Output Update*/

Write 11 Hex to Serial Port

/* Writes to Communications Register Setting Next Operation as Read

From Data Register*/

Read 24-Bit Data From Serial Port

/* Read Conversion Result from AD7731’s Data Register*/

Increment CHANNEL

/* Increments Channel Address*/

If CHANNEL = 7Hex Then Set CHANNEL = 4 Hex

/* Resets Channel Address*/

Loop to CH_LOOP