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Chapter 4 Theory of Operation
© National Instruments Corporation 4-3 PCI-1200 User Manual
The PCI-1200 generates an interrupt in the following five cases (each of
these interrupts is individually enabled and cleared):
• When a single A/D conversion can be read from the A/D FIFO
memory.
• When the A/D FIFO is half-full.
• When a DAQ operation completes, including when either an
OVERFLOW or an OVERRUN error occurs.
• When the digital I/O circuitry generates an interrupt.
• When a rising edge signal is detected on the DAC update signal.
Timing
The PCI-1200 uses two 82C53 counter/timer integrated circuits for internal
DAQ and DAC timing and for general purpose I/O timing functions.
Figure 4-3 shows a block diagram of both groups of timing circuitry
(counter groups A and B).