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VME bus vs PXI bus | Difference between VME bus and PXI bus

This page compares VME bus vs PXI bus and mentions difference between VME bus and PXI bus.

VME Bus

VME has been designed as platform which fully supports multiprocessing feature as required by all the controllers similar to computer boards. The hardware part implements arbitration while software overhead is not there in VME. VME is asynchronous bus.

Following are the features of VME platform.
• Stable platform
• Good interconnect (backplane)
• Same CPU board works in all the plots
• Good interrupt structure
• Good multiprocessing without software
• 21 slots in a single chassis
• Over 700 Mbps
• No standardized timing and synchronization
• Real time support

PXI Bus

PXI is the short form of PCI eXtensions for Instrumentation. It is rugged PC based platform for test and measurement and automation systems.

PXI combines PCI electrical bus with rugged, modular, Eurocard packaging of compact-PCI along with special synchronization buses and software. It is synchronous bus. PXI is high performance and lower cost platform.

PXI is governed by PXISA (i.e. PXI Systems Alliance) which is a group having more than 70 member companies.

Following are the features of PXI platform.
• Open multi-vendor standard (with more than 70 vendors) with over 1200 modules.
• Plug and Play
• More I/O pins and wide choice of instrumentation
• Faster bus transfer and lower latency
• Off the shelf bus software drivers
• 21 slots in a single chassis
• Over 6 Gbps
• Timing and synchronization with pico-second level accuracy
• Real time support in dual core processors
• continuous movement in processors (Dual core, Quad core etc.)
• Ability to connect with a wide variety of buses (e.g. GPIB, USB, LAN etc.)

There are two buses fall under PXI viz. PCI and PCI Express.

Tabular difference between VME and PXI buses

Following table mentions difference between VME and PXI buses.


Features VME PXI
Data Throughput(Max.) 700 Mbps System will have 6 Gbps while peripheral slot will have 2 Gbps.
EMI/EMC,
Required EMC testing,
electrical safety standard

No
No

Yes (section 3.9.1 of spec)
Yes (section 3.9.2 of spec)
Cooling
Defined Air Flow

No

Yes
Timing and Synchronization
Synchronization Clock
Trigger Lines

No
No

Yes
Yes
Power Voltages +5, -5.2, -2, +/12,+/-24 +5, +3.3, +/-12
Communications standardized protocols Yes, message based, Register based Yes, register based message based, peer to peer bus mastering peripherals



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