Support Question of the Week: To Save Board Space and Not Include a Connector on the PCB, How Should I Connect the Beagle USB Protocol Analyzer?

I am working on a new design that will be installed in a system. To do so, I need to save board space. My target USB bus is inside of an embedded system. To analyze and verify the results, I'll need to tap off the lines to monitor the USB bus. To use the Beagle USB 480 Protocol Analyzer, I think I'll only need to wire in GND and the D+/D- signal pair - is that correct?

Thanks for your question! Section 3.1 of the Beagle Protocol Analyzer User Manual describes the four main architectures for connecting devices to the Beagle analyzer.

Beagle USB Protocol Analyzer Connections Figure 1: Beagle USB Protocol Analyzer Connections

As the system that you will be analyzing is embedded, the architecture to use is probably (d), as shown above in Figure 1. You are correct that GND and the D+/D- signals are needed. The D+/D- signal path of a USB does not have to be broken to be monitored by a Beagle USB protocol analyzer. The VBUS, GND, D+, and D- lines can be connected to either the Type A or Type B connector on the Beagle analyzer using "T" connections.

The method of connecting the analyzer to the embedded bus will vary depending on the accessibility of the signals on the target system. You may need to cut open a USB cable to attach the wires to the target system.

If the signal lines are easily accessible through a header or test pads, then connecting to it should be straightforward. If the signals are not easily accessible, the wires may need to be soldered directly to IC pins or to traces on the printed circuit board. Extreme caution of this is required; note that Total Phase cannot be held responsible if equipment is damaged from such activities.

Following are some of the factors to consider when monitoring an embedded USB:

  • How to connect to the signal lines
  • Ensuring signal integrity between the target device and the Beagle USB analyzer
  • Ensuring 5V is present on the VBUS so that the Beagle USB analyzer recognizes the presence of the host

For details about connecting the Beagle USB analyzer, please refer to the knowledge base article Monitoring an embedded USB with a Beagle USB Protocol Analyzer.

For more information, please refer to the following documents:

We hope this answers your question. If you have other questions about our host adapters or other Total Phase products, feel free to email us at or submit a request for technical support.

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