In the early 2000’s, the performance of the PCI bus, which is the backbone of PXI, was greatly enhanced through the development of PCI Express (PCIe). Within a few years, PCIe signaling was brought into the PXI standard, resulting in PXI Express (PXIe).
With the introduction of PXIe, the PXI platform saw multiple performance enhancements such as increasing backplane bandwidth 45X from 132 MB/s to 6 GB/s and improving PXI timing and synchronization by incorporating a 100 MHz differential reference clock and differential trigger lines. Additionally, since data is sent serially through pairs of transmit and receive connections with PCIe, data on PXIe can transfer at 250 MB/s per direction, and multiple lanes can be grouped together to increase bandwidth to a particular slot.
PXI and PXIe – A Symbiotic Relationship
It is important to recognize that PXIe is not intended to be a replacement for PXI. Thus, one of the key features of the PXIe platform is that it maintains backwards compatibility for PXI software and hardware, making it fully compatible with existing PXI systems. From the software side, this is possible because PCIe uses the same operating system (OS) and driver model as PCI, which means the OS and driver model are the same for PXI and PXIe. This software compatibility is also ensured by the PCI Special Interest Group (PCI-SIG).
On the hardware side, many PXIe chassis provide PXI slots, PXIe slots, and hybrid slots. If this is the case, you can use PXI and PXIe peripheral modules together in a single chassis. However, some PXIe chassis only have PXI hybrid-compatible slots and do not have full PXI peripheral slots, therefore the chassis will not accept standard PXI peripheral cards. Additionally, if a chassis is a PXI chassis and not a PXIe chassis, it will not be compatible with any PXIe cards since it can only accommodate either a PXI peripheral module or hybrid slot-compatible PXI module.
Is PXIe Right for Your Application?
As previously mentioned, PXIe does not replace PXI. Instead, PXIe helps expand the PXI platform by offering a bus with higher data transfer speeds and the lowest latency of all mainstream commercial off-the-shelf (COTS) test and measurement bus technologies. In general, PXIe delivers latency comparable to – and in some cases better than – PXI.
However, many applications, including general data acquisition and motion control, do not require the increased bandwidth of PXIe. Thus, PXIe should not be used in applications where the speeds offered by PXI are suitable, because even though the transmission speed is faster with PXIe, a system may have features that reduce speeds elsewhere in the circuit. Overall, instead of replacing PXI, PXIe gives engineers the ability to use COTS technology to create unique applications for high-speed imaging and high-channel-count data acquisition systems where expensive engineered solutions were previously the only option.
To ensure you are making the best decision for your application needs, it is best to consult with a third-party expert, such as General Technics. Our engineers will work with you to understand the exact requirements of your application and help navigate the options offered by PXI and PXIe technology.