Analog Input And Data Acquisition Circuitry; Analog Input Circuitry; Figure 4-3. Analog Input And Data Acquisition Circuitry Block Diagram - National Instruments Corporation DAQCard-500 User Manual

Chapter 4
When you first insert the card, the system examines information stored in the DAQCard-500
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.

Analog Input and Data Acquisition Circuitry

The DAQCard-500 has 8 channels of analog input with 12-bit A/D conversion. Using the timing
circuitry, the DAQCard-500 can also automatically time multiple A/D conversions. Figure 4-3
shows a block diagram of the analog input and data acquisition circuitry.
PCMCIA
I/O
Channel
Interface
Interrupt
Interface
1 MHz

Figure 4-3. Analog Input and Data Acquisition Circuitry Block Diagram

Analog Input Circuitry

The analog input circuitry consists of an input multiplexer, a buffer, and a 12-bit sampling ADC.
The 12-bit output is sign-extended to 16 bits, then stored in a 16-word-deep FIFO memory.
The input multiplexer is an 8-channel CMOS analog input multiplexer. The input multiplexer
selects one of 8 analog input channels (channels 0 through 7). With the input multiplexer stage,
input overvoltage protection of ± 25 V is available, powered on or off.
The DAQCard-500 uses a 12-bit successive-approximation ADC. The ADC has a fixed input
range of ±5 V.
When an A/D conversion is complete, the ADC clocks the result into the A/D FIFO. The A/D
FIFO is 16 bits wide and 16 words deep. This FIFO serves as a buffer to the ADC and has two
© National Instruments Corporation
16-Word 12-Bit
16 12
FIFO, Sampling
Sign
Data
A/D
Extension
Data
A/D RD
DAVAIL
OUT0
MSM82C54
Buffer
ADC
A/D Timing
4-3
Theory of Operation
Input
Mux
8
8-Channel
Single-
Ended
3
Scanning Counter
EXTCONV*
1 MHz
DAQCard-500 User Manual