A bus with low (meaning good) latency would introduce less delay between the time data was transmitted on one end and processed on the other end. By analogy, if we were to compare an instrumentation bus to a highway, bandwidth would correspond to the number of lanes and the speed of travel, while latency would correspond to the delay introduced at the on and off-ramps. Latency measures the delay in data transmission across the bus. Bandwidth versus Latency for Instrumentation Buses

Figure 1 charts the bandwidth (and latency) of all the instrumentation buses examined in this paper.įigure 1.

The functionality and personality of a virtual or synthetic instrument is defined by software in most cases, this means data must be moved to a host PC for processing and analysis. High-speed data transfer is particularly important for virtual and synthetic instrumentation architectures. Bandwidth is important in applications such as complex waveform generation and acquisition as well as RF and communications applications. Most users recognize the importance of bandwidth because it affects whether their data can be sent across the bus to or from a shared host processor as fast as it is acquired or generated and how much onboard memory their instruments will need. A bus with high bandwidth is able to transmit more data in a given period than a bus with low bandwidth. Bandwidth measures the rate at which data is sent across the bus, typically in MB/s (106 bytes per second). When considering the technical merits of alternative buses, bandwidth and latency are two of the most important bus characteristics. Specific bus technologies discussed below include GPIB, USB, PCI, PCI Express, and Ethernet/LAN/LXI.įirst, it is important to outline the relevant performance criteria for instrument control buses, in order to set a baseline for evaluation and comparison. This paper presents a head-to-head comparison of the most popular instrumentation buses, so that test engineers can make informed decisions when choosing the bus and platform technologies to meet their application-specific needs. The challenge for today’s test engineer is not to choose a single bus or platform on which to standardize every single application, but to choose a bus or platform appropriate for a specific application or even a specific part of an application. In reality, it is most likely that two or more bus technologies will continue to coexist in future test and measurement systems because each bus has its own strengths. Some test and measurement vendors and industry pundits have claimed that one of these buses, by itself, represents a solution for all instrumentation needs. Today, USB, PCI Express, and Ethernet/LAN have gained attention as attractive communication options for instrument control.

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