Chapter 4
Theory of Operation
DAQCard-1200 User Manual
4-12
ni.com
Digital I/O
The DIO circuitry has an 82C55A integrated circuit. The 82C55A is a
general-purpose programmable peripheral interface (PPI) containing
24 programmable I/O pins. These pins represent the three 8-bit I/O ports
(A, B, and C) of the 82C55A, as well as PA<0..7>, PB<0..7>, and
PC<0..7> on the DAQCard-1200 I/O connector. Figure 4-6 shows the DIO
circuitry.
Figure 4-6.
Digital I/O Circuitry
All three ports on the 82C55A are TTL-compatible. When enabled, the
digital output ports are capable of sinking 2.4 mA of current and sourcing
2.6 mA of current on each DIO line. When the ports are not enabled, the
DIO lines act as high-impedance inputs.
PCMCIA
I/O
Channel
PCMCIA
P
or
t
Interf
ace
Data
8
Decode
Circuitry
DATA<0..7>
DIO RD/WRT
2
82C55A
Programmable
Peripheral
Interface
8
8
8
I/O
Connector
PA<0..7>
PB<0..7>
PC<0..7>
To
Interrupt
Control
PC0
PC3
Содержание DAQPad-1200
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