Chapter 3 Theory of Operation
National Instruments Corporation 3-3 PC-LPM-16/PnP User Manual
PC I/O Channel Interface Circuitry
The PC I/O channel interface circuitry consists of an address bus, a data
bus, interrupt lines, and several control and support signals. The
components making up the PC-LPM-16PnP PC I/O channel interface
circuitry are shown in Figure 3-2.
Figure 3-2.
PC I/O Interface Circuitry Block Diagram
The circuitry consists of Plug and Play address decoders, data buffers,
I/O channel interface timing control circuitry, and interrupt control
circuitry. The circuitry monitors address lines SA4 through SA15 to
generate the board enable signal, and uses lines SA0 through SA3 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 bidirectional data lines based on whether the transfer is a read or
write operation.
The interrupt control circuitry routes any enabled interrupts to the
selected interrupt request line. The PC-LPM-16PnP has six interrupt
Address Bus
Control Lines
Data Bus
IRQ
Register Selects
Read & Write Signals
Internal Data Bus
Interrupt Requests
Plug and 
Play Circuitry
Timing
Interface
Data
Buffers
Plug and
Play Interrupt
Control
Address
Decoder
PC I/O Channel
a.Book : g.chapter 3 Page 3 Wednesday, November 20, 1996 6:36 PM