Theory of Operation Chapter 3
Lab-NB User Manual 3-2 © National Instruments Corporation
The following are the major components making up the Lab-NB board:
• NuBus interface circuitry
• Analog input and DAQ circuitry
• Analog output circuitry
• Digital I/O circuitry
• Timing I/O circuitry
DAQ functions can be executed by using the analog input circuitry and some of the timing I/O
circuitry. The internal data and control buses interconnect the components. The theory of
operation for each of these components is explained in the remainder of this chapter. The theory
of operation for the DAQ circuitry is included with the discussion of the analog input circuitry.
NuBus Interface Circuitry
The Macintosh NuBus is a 32-bit multiplexed address and data bus with a 10-MHz bus clock. In
addition, the NuBus provides interface signals for interrupt and read/write operations. The
NuBus interface circuitry consists of a starting address detector, interface timing signals, and
address-decoder circuitry. This interface circuitry generates the signals necessary to control and
monitor the operation of the Lab-NB multifunction circuitry.
Data
Transceivers Internal Data Bus
AD<0..31>
16 16
Address
Decoder
NuBus
Interface
Timing
1-MHz
Timebase
2-MHz
Timebase
10-MHz Clock Register Selects
Read & Write Signals
1-MHz Clock
(to 8253s)
2-MHz Clock
(to 8253s)
÷ 5
÷ 10
NuBus
Figure 3-2. NuBus Interface Circuitry Block Diagram