Theory of Operation
Chapter 3
AT-MIO-16D User Manual
3-4
© National Instruments Corporation
accessed, when the board is ready for another transfer, and the data bit size of the current I/O
transfer.
The interrupt control circuitry routes any enabled interrupt requests to the selected interrupt request
line. The interrupt requests are tristate output signals allowing the AT-MIO-16D board to share the
interrupt lines with other devices. Eleven interrupt request lines are available for use by the
AT-MIO-16D: IRQ3, IRQ4, IRQ5, IRQ6, IRQ7, IRQ9, IRQ10, IRQ11, IRQ12, IRQ14, and
IRQ15. Five different interrupts can be generated by the MIO-16 circuitry of the AT-MIO-16D:
¥
When an A/D conversion is available to be read from the A/D FIFO memory
¥
When a data acquisition operation completes
¥
When a DMA terminal count pulse is received
¥
When a rising edge signal is detected on the OUT2 pin of the Am9513A Counter/Timer
¥
When either an OVERFLOW or an OVERRUN error occurs
Each one of these interrupts is individually enabled and cleared. See Chapter 4,
Programming
, for
more information about programming with interrupts.
The DMA control circuitry generates DMA requests whenever an A/D measurement is available
from the A/D FIFO, if the DMA transfer is enabled. The DMA circuitry supports full PC AT I/O
channel 16-bit DMA transfers. DMA channels 5, 6, and 7 of the PC AT I/O channel are available
for such transfers. With the DMA circuitry, either single-channel transfer mode or dual-channel
transfer mode can be selected for DMA transfer.
Analog Input and Data Acquisition Circuitry
The AT-MIO-16D handles 16 channels of analog input with software-programmable gain and 12-
bit A/D conversion. In addition, the AT-MIO-16D contains data acquisition circuitry for automatic
timing of multiple A/D conversions and includes advanced options such as external triggering,
gating, and clocking. Figure 3-3 shows a block diagram of the analog input and data acquisition
circuitry.
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