Data Translation DT9824, User Manual, Page: 53 / 102

Principles of Operation
53
In software, the analog input value is returned as a code. To convert the code to voltage, use
the following formulas:
LSB = FSR
2
N
Vin = Code * LSB + Offset
where,
• LSB is the least significant bit.
• FSR is the full-scale range. For the DT9824, the full-scale range is 20.
• N is the input resolution (24 bits).
• Vin is the analog voltage.
• Code is the raw count used by the software to represent the voltage.
• Offset is the actual minus full-scale value. The minus full-scale value is –10 V.
For example, if the software returns a code of 2010 for the analog input operation, determine
the analog input voltage as follows:
LSB = 20 = 0.00000119 V
16777216
Vin = 2010 * 0.00 –10.0
Vin = –9.998 V
Data Transfer
The DT9824 module transfers data to a user buffer that you allocate in the host computer.
Keep the following recommendations in mind when allocating user buffers for continuous
analog input operations on the DT9824 module:
• Allocate a minimum of two user buffers.
• Specify the width of the buffer as 4 bytes.
Data is written to the allocated buffers continuously until no more empty buffers are available
or you stop the operation. The data is gap-free.
Error Conditions
The DT9824 module can report an A/D overrun error if the A/D sample clock rate is too fast.
The error occurs if a new A/D sample clock pulse occurs while the ADC is busy performing a
conversion from the previous A/D sample clock pulse. The host computer can clear this error.
To avoid this error, use a slower sampling rate.