PXI vs. PCI: Key Differences in Bus Standards

This article explores the distinctions between PXI (PCI eXtensions for Instrumentation) and PCI (Peripheral Component Interconnect), two important bus standards in the world of computer hardware and instrumentation.

PXI: PCI eXtensions for Instrumentation

PXI, which stands for PCI eXtensions for Instrumentation, is a modular instrumentation platform built upon the PCI and PCI Express standards. These standards are overseen by the PCISIG. PXI has gained immense popularity, especially in the test and measurement industry, effectively becoming a successor to the older GPIB standard. Currently, the PXI System Alliance boasts about 70 vendor members, showcasing its wide adoption.

The latest iterations of PXI utilize PCI Express, allowing for impressive data throughputs of up to 6 Gbps. Here are some key features of the PXI backplane:

• 100 MHz differential system reference clock: Provides a stable timing reference.
• 10 MHz reference clock signal: Another important timing signal for system synchronization.
• Differential star trigger: Allows for precise triggering of modules.
• Star trigger bus: This bus features matched-length traces, minimizing delays and timing skew between modules.
• High-speed trigger bus: Facilitates the transmission of high-speed timing and trigger signals.
• Differential signals for multichassis synchronization: Enables synchronized operation across multiple chassis.

For a more in-depth comparison, you might want to explore resources on PXI Bus vs. VME Bus.

PCI: Peripheral Component Interconnect

PCI, or Peripheral Component Interconnect, is a local bus standard originally developed by Intel. It’s a fundamental part of the PXI architecture but also has a life of its own as a widely used standard in computer systems. PCI successfully replaced the older ISA bus and is implemented in a parallel multi-drop configuration.

PCI is incredibly versatile, supporting a wide range of peripherals and high-performance devices. It’s commonly used for applications like graphics, full-motion video, SCSI, and LAN connections.

Here are the technical specifications of the PCI bus:

• 64-bit bus capabilities: While it can support a 64-bit bus, it’s typically implemented as a 32-bit bus.
• Operating Speeds: It operates at either 33MHz or 66MHz.
• Data Rate: A 32-bit bus running at 33MHz can achieve a data rate of approximately 133 Mbyte/sec.

Key Differences Summarized

In essence, while PXI leverages PCI technology, it builds upon it to cater specifically to the needs of instrumentation and measurement, adding features designed for precise timing and modular system design. PCI, on the other hand, serves as a more general-purpose standard for connecting various components within a computer system.