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Chapter 3
Theory of Operation
© National Instruments Corporation
3-17
AT-MIO-16D User Manual
The block diagram in Figure 3-9 illustrates the key functional components of the AT-MIO-16D
DIO-24 circuitry.
I/O Connector
Interrupt
Control
Circuitry
82C55A
PPI
PC AT I/O
Channel
Control
Circuitry
Address
Decoder
Bus
Transceivers
PA
PB
PC
/
8
/
8
/
8
PC3
PC0
+5 V
PC AT I/O Channel
1A Fuse
Figure 3-9. AT-MIO-16D DIO-24 Block Diagram
DIO-24 Interrupt Control Circuitry
The interrupt level used by the DIO-24 circuitry of the AT-MIO-16D is selected by the onboard
jumper W13. Another onboard jumper, W14, is used to enable interrupts from the DIO-24
circuitry. The setting for W14 selects PC2, PC4, or PC6 as the active low interrupt enable signal.
Selecting N/C for W14 disables interrupts from the DIO-24 circuitry. When the onboard jumpers
are set to enable interrupts, the 82C55A can be programmed to generate an interrupt request by
setting INTRA for Group A or INTRB for Group B. When interrupts are enabled for Group A, an
active high signal on the PC3 line generates an interrupt request. When interrupts are enabled for
Group B, an active high signal on the PC0 line generates an interrupt request.
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