Datasheet AD7708, AD7718 (Analog Devices) - 33

AD7708/AD7718
1. Write to the ADCCON register to select the channel to be 4. When the data is read, increment the channel address pointer calibrated, its input range, and operation in unipolar or to select the next channel, poll the RDY pin, or RDY bit in bipolar mode. the status register, and again read the data. Continue until all channels have been read. 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.
CYCLE THROUGH AND READ ALL CHANNELS
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.
WRITE TO MODE REGISTER SELECTING CONTINUOUS CONVERSION MODE
3. The calibration is initiated following the write to the mode register. The user then needs to determine when the calibra- tion is complete. This can be performed in two ways, by
WRITE TO ADCCON SELECTING CHANNEL N
polling the RDY pin or flag or by monitoring the MD2,
AND ITS OPERATING RANGE
MD1, MD0 bits in the mode register. These bits are reset to 0, 0, 1 when the calibration is complete. The flowchart uses
POLL RDY PIN
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.
RDY LOW?
Using system calibration the user must supply the full-scale signal to the analog inputs for the duration of the calibration.
NO
Again the MD2, MD1, MD0 bits in the mode register are
YES
monitored to determine when the calibration is complete.
WRITE TO COMMUNICATIONS REGISTER SETTING UP
Figure 18 shows a flowchart detailing the necessary program-
NEXT OPERATION TO BE A READ OF DATA REGISTER
ming steps required to cycle through and read data results from
AND THEN READ DATA RESULT
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
INCREMENT CHANNEL ADDRESS (N = N+1)
channels in a multiplexed application. 1. The AD7708/AD7718 is put into continuous conversion mode. In this mode the part continually converts on the
ALL NO
specified channel and the RDY line indicates when valid
CHANNELS READ
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/
YES
bipolar mode.
END
3. In this flowchart hardware polling of the RDY line is per- formed to determine when it is valid to read data from the Figure 18. Multichannel Read Operation 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. REV. 0 –33–