AD7708 datasheet(32/44 Pages) AD

32 / 44 page

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AD7708/AD7718

Configuring the AD7708/AD7718

All user-accessible registers on the AD7708 and AD7718 are

accessed via the serial interface. Communication with any of

these registers is initiated by first writing to the Communica-

tions Register. Figures 16, 17, and 18 show flow diagrams for

initializing the ADC, a sequence for calibrating the ADC chan-

nels, and a routine that cycles through and reads all channels.

Figure 16 shows a flowchart detailing necessary programming

steps required to initialize the ADC. The following are the general

programming steps required:

1. Configure and initialize the microcontroller or microprocessor

serial port.

2. Initialize the AD7708/AD7718 by configuring the following

registers:

a. IOCON to configure the digital I/O port.

b. FILTER to configure the update rate for each channel.

c. ADCCON to select the active input channel, select

the analog input range, and select unipolar or bipolar

operation.

d. MODE to configure the operating mode. The mode

unbuffered operation of the AINCOM input, 8-/10-

channel mode of operation and reference select along

with the selection of conversion, calibration or idle

modes of operation.

All 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 the specified register. When each sequence

is complete, the ADC defaults to waiting for another write to

the communications register to specify the next operation.

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A WRITE TO THE MODE

OPERATION

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A WRITE TO THE ADC

CONTROL REGISTER. CONFIGURE ADCCON

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A WRITE TO THE FILTER

UPDATE RATE

WRITE TO COMMUNICATIONS REGISTER SELECTING

NEXT OPERATION TO BE A WRITE TO THE IOCON

POWER-ON/RESET FOR AD7708/AD7718

CONFIGURE AND INITIALIZE

C/ P SERIAL PORT

START

Figure 16. Initializing AD7708/AD7718

END

CAL

ANOTHER

CHANNEL

WRITE TO MODE REGISTER SELECTING

FULL-SCALE CALIBRATION

WRITE TO MODE REGISTER SELECTING

ZERO-SCALE CALIBRATION

WRITE TO ADCCON SELECTING CHANNEL AND CONFIGURING

INPUT RANGE AND UNIPOLAR/BIPOLAR MODE

CALIBRATION ROUTINE

MD BITS

= 001?

YES

MD BITS

= 001?

YES

Figure 17. Calibrating the AD7708/AD7718

Figure 17 shows a flowchart detailing necessary programming

steps required when calibrating the AD7708/AD7718. The

AD7708/AD7718 have dedicated calibration register pairs for

each of the fully-differential input channels. Having a dedicated

part of the initialization and the ADC picks up the relevant

coefficients for each channel during normal operation. When

operating is pseudo-differential mode channels share calibration

ured with the same operating conditions to avoid having to

calibrate each time a channel is switched, especially with chop

mode disabled. The AD7708/AD7718 are factory-calibrated

with chop mode enabled and, therefore, if the ADC is operated

at the same conditions as the factory-calibration field calibra-

tions will not be required. Extremely low offset error and offset

and gain drift errors are a by product of the chopping scheme.

When operating with chop mode disabled, the user can achieve

faster throughput times. An offset calibration is required with

chop disabled when a gain or temperature change occurs. The

following are the general programming steps required when

calibrating a channel on the AD7708/AD7718.

AD7708 数据表(PDF) 32 Page - Analog Devices

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