National Instruments 700 - Manual (Page 40)

Chapter 4 Theory of Operation
© National Instruments Corporation 4-3 DAQCard-700 User Manual
When you first insert the card, the system examines information stored in the DAQCard-700
Card Information Structure. This data is used to configure the card appropriately for the system
in which it is used. When the system has assigned the card to a section of memory, it updates the
PCMCIA control registers and initializes the card.
The rest of the circuitry consists of address decoders, data buffers, I/O channel interface timing
control circuitry, and interrupt control circuitry. The circuitry monitor uses CE1* (controlled by
the PCMCIA Card and Socket Services Software) as the card enable signal, and uses lines A0
through A4 plus timing signals to generate the onboard register select signals and read/write
signals. The data buffers control the direction of data transfer on the bi-directional data lines
based on whether the transfer is a read or write. The interrupt control circuitry routes any
enabled interrupts to the IREQ* line, which is routed to an available interrupt request line by the
system motherboard. The DAQCard-700 generates interrupts in three different situations:
• When a prescribed number of A/D conversions can be read from FIFO
• When an active low-level signal is detected on the EXTINT* line
• When a rising-edge signal is detected on counter 2 output
Each one of these interrupts is individually enabled and cleared. If you want more detailed
information on externally generating interrupts, refer to the optional DAQCard-700 Register-
Level Programmer Manual.
Analog Input and Data Acquisition Circuitry
The DAQCard-700 has 16 channels of analog input with 12-bit A/D conversion. Using the
timing circuitry, the DAQCard-700 can also automatically time multiple A/D conversions.
Figure 4-3 shows a block diagram of the analog input and data acquisition circuitry.