AD7708 Analog Devices, AD7708 Datasheet - Page 33

• Manufacturer Part Number: AD7708
• Description: 16-Bit 8/10-Channel, Low Voltage, Low Power, Sigma Delta ADC
• Manufacturer: Analog Devices

Specifications of AD7708

• Resolution (bits): 16bit
• # Chan: 10
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOIC,SOP

1. Write to the ADCCON register to select the channel to be
2. Write to the mode register selecting chop or nonchop mode
3. The calibration is initiated following the write to the mode
4. The next step is to perform the full-scale calibration. Full-scale
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
2. The ADCCON register is written to select the channel
3. In this flowchart hardware polling of the RDY line is per-
calibrated, its input range, and operation in unipolar or
bipolar 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.
register. The user then needs to determine when the calibra-
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.
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.
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.
for conversion, its input range and operation is unipolar/
bipolar mode.
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.
WRITE TO COMMUNICATIONS REGISTER SETTING UP
NEXT OPERATION TO BE A READ OF DATA REGISTER
AND THEN READ DATA RESULT
WRITE TO ADCCON SELECTING CHANNEL N
AND ITS OPERATING RANGE
INCREMENT CHANNEL ADDRESS (N = N+1)
WRITE TO MODE REGISTER SELECTING
CONTINUOUS CONVERSION MODE
NO
NO
CYCLE THROUGH AND
READ ALL CHANNELS
POLL RDY PIN
CHANNELS
READ
LOW?
RDY
ALL
END
AD7708/AD7718
YES
YES