National Instruments AT-AI-16XE-10, Programmer'S Manual

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Chapter 2 Theory of Operation
© National Instruments Corporation 2-23 AT-MIO E Series RLPM
many times a buffer should be repeated. These counters define an analog
output sequence.
The DAQ-STC will transfer the data values for the next update after each
update pulse. This data transfer will be from the analog output FIFO. Some
of the boards have large 2 kword FIFOs; others are zero-deep virtual FIFOs.
The large FIFOs are true FIFOs, where data can be written to the FIFOs so
long as they are not full and can be read from when they are not empty. In
this case, the DAQ-STC will transfer the data from the FIFO to the DACs
when the FIFO is not empty. If the FIFO is empty, the DAQ-STC will delay
the transfer until more data is written into the FIFO.
The zero-deep virtual FIFOs are not true FIFOs, but they do provide a
software compatible method for waveform generation. When the
DAQ-STC generates an update signal and is ready to transfer data, the
DAQ-PnP will clear the FIFO full flag. This FIFO full flag can be used by
interrupts or DMA to transfer data to the virtual FIFO. The virtual FIFO
will not actually buffer the data, instead it will transfer it directly to the first
buffer of the destination DAC. After the data has been transferred, the
DAQ-PnP will set the FIFO full flag, indicating that no more data is
required. Note that the half-full and empty flags do not provide useful
information for data transfer and should not be used.
The large FIFOs can also be used to generate repetitive waveforms at very
high speeds and without using any bus bandwidth. The FIFOs can be
loaded with the desired waveform and the DAQ-STC can be programmed
to retransmit the same FIFO data to the DACs over and over. When the
FIFO is empty, the retransmit signal is asserted, which restores that FIFO
data to its original state.
When both DACs are used in waveform generation, the data in the FIFO is
interleaved; in other words, every alternate sample belongs to one DAC.
Digital I/O Circuitry
The AT E Series boards have eight digital I/O lines. Each of the eight
digital lines can be individually programmed to be input or output, if used
in parallel. For serial data transfer, DIO4 is used as the serial data in pin,
and DIO0 is used as the serial data out pin.
You can use handshaking with the EXTSTROBE* pin to do either parallel
or serial data transfer. Refer to the DAQ-STC Technical Reference Manual
for more details on the DIO features.