National Instruments DAQ PCI-1200, Руководство пользователя

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Chapter 4 Theory of Operation
PCI-1200 User Manual 4-12 © National Instruments Corporation
voltage increment corresponding to an LSB change in the digital code
word. For both outputs:
DAC Timing
There are two modes in which you can update the DAC voltages. In
immediate update mode , the DAC output voltage is updated as soon as you
write to the corresponding DAC. In delayed update mode , the DAC output
voltage does not change until a low level is detected either from counter A2
of the timing circuitry or EXTUPDATE*. This mode is useful for
waveform generation. These two modes are software selectable.
Digital I/O
The digital I/O circuitry has an 82C55A integrated circuit. The 82C55A
is a general purpose programmable peripheral interface 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 PCI-1200 I/O connector. Figure 4-6 shows the digital I/O
circuitry.
Figure 4-6. Digital I/O Circuitry
1 LSB
10
V
4 095
,
--------------- =
82C55A
Programmable
Peripheral
Interface
DIO RD/WRT
DATA<0..7>
PC0
PC3
PC<0..7>
PB<0..7>
PA<0..7>
I/O Connector
2
8
8
8
PCI Bus
Digital
Control
Logic
MITE
PCI
Interface
Chip
Data/Address
Interface Control
Error Reporting
Arbitration
System
Interrupt
1
2
2
2
6
37
Address
Data
Control
Interrupt
1
4
8
5