4.6 A/D Converter and Data FIFO
The DAQP card always assumes a bipolar input range of ±10V if the gain is one. The output data format will always be in 2's complement (and left justified for
The A/D converter, once triggered, will complete conversion for every analog input channel specified in the scan list at the specified scan speed and then feed the results into the data FIFO. In between scans, the DAQP card waits until another trigger is received
The data FIFO has two programmable thresholds, one for almost full and the other for almost empty. The DAQP card uses the almost full threshold and ignores the other one.
The data FIFO should always be flushed prior to using the arm/trig command to start data acquisition. When the FIFO is flushed or emptied by the host reading its content, the FIFO empty flag will be set. As long as there are samples left in the data FIFO, the empty flag will be cleared.
When the number of data samples in the FIFO becomes greater than the programmed almost full threshold, the almost full flag is set. When the number becomes less than or equal to the specified almost full threshold, the flag will be cleared. On power up or reset, the threshold is defaulted at 7 bytes to full (3.5 samples). Correct setting of the threshold will help achieve optimal performance of the card.
When the FIFO is full, the full flag will be set, and no more samples can be written into the FIFO. At the end of each scan, the DAQP card will set the data lost flag if the data FIFO is already full. This flag will not be set before or during the scan, but at the end of it. Once the data lost flag is set, it will not be cleared until the status register is read.
The data lost bit in the status register (base + 2) will be set when data continues to enter the A/D data FIFO while it is already full. With the
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