AD7708 datasheet(33/44 Pages) AD

33 / 44 page

REV. 0

AD7708/AD7718

–33–

1. Write to the ADCCON register to select the channel to be

calibrated, its input range, and operation in unipolar or

bipolar mode.

2. Write to the mode register selecting chop or nonchop mode

of operation, select the reference, buffered/unbuffered opera-

tion on the AINCOM, and select zero-scale offset calibration.

Zero-scale calibration can be either self-calibration, where

the ADC determines the zero point internal to the ADC, or a

system calibration where the user must supply the zero-scale

voltage to the input for the duration of the calibration.

3. The calibration is initiated following the write to the mode

tion is complete. This can be performed in two ways, by

polling the

RDY pin or flag or by monitoring the MD2,

MD1, MD0 bits in the mode register. These bits are reset to

0, 0, 1 when the calibration is complete. The flowchart uses

polling of the mode bits in the mode register to determine

when the calibration is complete.

4. The next step is to perform the full-scale calibration. Full-scale

calibration can be a self-calibration or system calibration.

Using system calibration the user must supply the full-scale

signal to the analog inputs for the duration of the calibration.

Again the MD2, MD1, MD0 bits in the mode register are

monitored to determine when the calibration is complete.

Figure 18 shows a flowchart detailing the necessary program-

ming steps required to cycle through and read data results from

all channels in a multiplexed application. This flowchart assumes

that all channels have been previously calibrated. The following

are the general programming steps required when reading all

channels in a multiplexed application.

1. The AD7708/AD7718 is put into continuous conversion

mode. In this mode the part continually converts on the

specified channel and the

RDY line indicates when valid

data is available to be read from the data register.

2. The ADCCON register is written to select the channel

for conversion, its input range and operation is unipolar/

bipolar mode.

3. In this flowchart hardware polling of the

RDY line is per-

formed to determine when it is valid to read data from the

converter. When

RDY is low, valid data is available in the

data register. The

RDY line is set high on a channel change

and will not go low until a new valid data word is available.

Alternatively, the RDY bit in the status register can be polled

in software to determine when to read data from the converter.

4. When the data is read, increment the channel address pointer

to select the next channel, poll the

RDY pin, or RDY bit in

the status register, and again read the data. Continue until all

channels have been read.

POLL RDY PIN

WRITE TO ADCCON SELECTING CHANNEL N

AND ITS OPERATING RANGE

END

WRITE TO COMMUNICATIONS REGISTER SETTING UP

NEXT OPERATION TO BE A READ OF DATA REGISTER

AND THEN READ DATA RESULT

WRITE TO MODE REGISTER SELECTING

CONTINUOUS CONVERSION MODE

CYCLE THROUGH AND

READ ALL CHANNELS

RDY

LOW?

YES

ALL

CHANNELS

READ

YES

INCREMENT CHANNEL ADDRESS (N = N+1)

Figure 18. Multichannel Read Operation

AD7708 数据表(PDF) 33 Page - Analog Devices

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