Military bus protocol testing

The oscilloscopes are. An oscilloscope measures the change in voltage level of electrical as time passes. An oscilloscope has a screen used as a graphical display, with voltage level shown on the vertical axis (Y) and time on the horizontal axis (X). The curve on the screen (representing the signal waveform), shows the changes in the voltage level, with time.

The trigger setting of an oscilloscope determines the time at which the oscilloscope starts to acquire the signal. The basic concept behind the oscilloscope trigger function is that some of the incoming signal is fed into a comparator circuit. When the voltage of the waveform reaches a previously defined trigger condition (e.g. it crosses a threshold level), the data acquisition is initiated. This is the main concept used to debug and decode bus signals, as single or multiple bits can be decoded during each trigger.

Modern digital oscilloscopes support a multitude of specific measurements and applications for troubleshooting circuits or checking the quality of acquired signals. Applications provided by Oscilloscopes can be generic or industry/segment specific.

Examples of MILCOM specific applications are the MILBUS or Arinc-429 bus trigger and decode for debug and, examples of generic applications are the compliance tests (such as USB or Ethernet), jitter measurements, frequency response analysis using Bode plot functions, power electronics measurements, digital signal analysis for mixed signal designs, EMI analysis, automotive radar debugging.

The general statements are:

• For non-sinusoidal waveforms like e.g. rectangular clock-signals, the oscilloscope bandwidth should be at least 3 times the clock signal fundamental frequency for decoding or debugging and 5 times the clock signal for compliance testing.
• For non-periodic signals the “rise time” t_r, i.e. the fastest / steepest edge of the signal, has to be considered. In this case, the required minimum oscilloscope bandwidth f_BW can be approximated using f_BW = 0.5 / t_r.

Considering a 160ns average rise time for the 1553B MILBUS, then the recommended oscilloscope should have a bandwidth of 3.5MHz. Rohde & Schwarz oscilloscope offer starts at 50MHz, so any oscilloscope could fit these bandwidth requirements.