National Instruments AT-MIO-64F-5, Руководство пользователя

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Theory of Operation Chapter 3
AT-MIO-64F-5 User Manual 3-18 © National Instruments Corporation
the waveform can be stopped by disabling the timer trigger. The result of this action is to leave
the DAC at some unknown value, for example the last updated value. The advantage of the
CYCLICSTOP control signal is that DAC updating ends gracefully. When this signal is set, the
waveform ends after it encounters the next retransmit signal. Thus, it will always end in a
known state at the end of the buffer.
FIFO Programmed Cyclic Waveform Generation
One step beyond the continuous waveform generation is the programmed cyclic waveform
generation. This mode is also available only when the entire buffer fits within the DAC FIFO.
Figure 3-14 shows the operation of this mode.
COUNTER 1, 2, or 5
5 4 3 2 1 0 5
DACFIFORT*
Figure 3-14. FIFO Programmed Cyclic Waveform Timing
In this case, one of the counters in the Am9513A Counter/Timer is programmed to count the
number of DAC FIFO Retransmit signals. When the counter counts the appropriate number of
occurrences, it terminates the waveform sequence. A bit is available in Status Register 1 to
indicate termination of a waveform sequence.
FIFO Pulsed Waveform Generation
Another step beyond cycle counting is pulsed waveform generation. Again, this mode is
applicable only if the entire buffer fits within the DAC FIFO. Figure 3-15 shows the operation
of this mode and the resulting waveform.
2 1 2 1 2 1 2 CTR 1
DACFIFORT*
CTR 2 Terminal Count
CTR 1 Output
Figure 3-15. FIFO Pulsed Waveform Generation Timing