Chapter 1
Getting Started
©
National Instruments Corporation
1-7
Local Bus
The PXI backplane local bus is a daisy-chained bus that connects each
peripheral slot with adjacent peripheral slots to the left and right as shown
in Figure 1-3. For example, the Slot 2 right local bus connects to the Slot 3
left local bus, and so on.
The left local bus signal lines on Slot 2 are used for the star trigger and do
not connect to Slot 1. The right local bus signal lines on Slot 4 are used for
SCXI communication.
Each local bus is 13 lines wide and can pass analog signals up to
42 V between cards or provide a high-speed TTL side-band digital
communication path that does not reduce the PXI bus bandwidth.
Initialization software uses the configuration information specific to
adjacent peripheral modules to evaluate local bus compatibility.
SCXI Control Slot
Slot 4 of the PXI backplane has connections for a PXI peripheral module
such as an NI PXI DAQ module, an NI PXI DMM module, or an
NI-Switch controller module to control the SCXI subsystem. These
connections use the available local bus right pins (PXI_LBR0:12). The
SCXI connection passes communication, timing, and low-voltage analog
bus signals between the SCXI subsystem and the PXI module in Slot 4.
Note
For more information about the local bus right pins, refer to the
PXI Specification
,
Revision 2.0
.
Trigger Bus
All slots on each PXI bus segment share eight PXI trigger lines. You can
use these trigger lines in a variety of ways. For example, you can use
triggers to synchronize the operation of several different PXI peripheral
modules. In other applications, one module located in Slot 2 can control
carefully timed sequences of operations performed on other modules in the
system. Modules can pass triggers to one another, allowing precisely timed
responses to asynchronous external events the system is monitoring or
controlling.
