National Instruments 320174B-01 用户手册

The starting-address-detecting circuitry on the Lab-NB matches address lines 23 through 21 to
the starting address specified by the slot in which the Lab-NB board is installed.  The remaining
address lines (19 through 0) are decoded by the Lab-NB address-decoding circuitry to generate
select signals for the registers on the board.  The NuBus interface timing signals are decoded by
the Lab-NB interface timing circuitry, which generates the proper read and write signals for the
remaining Lab-NB circuitry.  The Lab-NB board can cause interrupts in the Macintosh by
driving the NuBus NMRQ* interrupt line.

The Lab-NB provides eight channels of analog input with software-programmable gain and
12-bit A/D conversion.  Using the timing circuitry, the Lab-NB can also automatically time
multiple A/D conversions.  Figure 3-3 shows a block diagram of the analog input and DAQ
circuitry.

Sample-
and-Hold
Amp

NuBus

Mux

Counter

Data

Acquisition

Timing

ADC

Configuration

Register

Mux

Pro-
grammable
Gain Amp

ADC

A/D

FIFO

MUX CTR CLK

External Trigger

Counter/Timer

Signals

ADC WR

CONV
AVAIL

A/D
RD

EXT

CONV*

EXT

TRIG

ACH0
ACH1
ACH2
ACH3
ACH4
ACH5
ACH6
ACH7

12

12

16

3

4

A/D

Data

Data

Data

MUX
OUT

I/O Connector

GAIN0

GAIN1

GAIN2

Convert

Figure 3-3.  Analog Input and DAQ Circuitry Block Diagram