Troubleshooting Modern Serial Bus Signals with Siglent SDS Series Oscilloscopes

The Siglent SDS series digital storage oscilloscopes available from Circuit Specialists feature advanced triggering capabilities that are not available on most analog oscilloscopes. These advanced triggering functions are useful for troubleshooting glitches and dropouts as well as complex serial data streams. A brief tutorial will be presented with a simple example of the usefulness of these features.

In addition to the standard edge and slope triggering modes used in all oscilloscopes, the Siglent SDS series scopes provide advanced triggering capabilities — including video, slope, pulse, window, interval, drop out, runt, and pattern modes — that are invaluable in troubleshooting modern digital signals and waveforms. These oscilloscopes are also capable of triggering on and decoding the complex serial data streams used is essentially all modern electronic systems from industrial controls to automotive systems. Serial data such as the I2C, SPI, UART/RS232, CAN, and LIN formats are all presently supported.

This tutorial will focus on the Siglent SDS2074, SDS2104, and SDS2204 digital storage oscilloscopes, which feature four channels, 2 GSa/s real-time sampling rates (maximum), and up to 200 MHz bandwidth.

Video mode is useful for troubleshooting the signals found in video surveillance systems and supports NTSC, PAL, several HDTV formats, or a custom user-defined format. The oscilloscope may be set to trigger on specific pulses, video frames, or even video line numbers. A custom video trigger setup is available that allows the user to specify his or her own video standards with frame rates of 25, 30, 50, or 60 Hz and line numbers from 300 to 2000.

In slope, pulse, window, interval, and drop out modes, the user has the option of selecting the trigger signal based on the width of the pulse or time period of interest. The choices are < (less than), > (greater than), <> (within a range), and >< (outside a range). The range is an adjustable slope or pulse width in the range of 20 nanoseconds to 10 seconds. This mode is useful for viewing and troubleshooting complex analog or digital signals that may vary in amplitude and time and may or may not be repetitive in nature. Serial Bus signals may be easily viewed using this triggering mode if one does not need to decode the signal.

The runt triggering mode is extremely useful in observing and capturing those elusive “runt” pulses that are essentially impossible to view on an analog or low-cost digital oscilloscope. The user has the option of <, >, <>, or >< triggering conditions as well as the amplitude value and polarity of the unacceptable pulse.

Pattern triggering mode uses both channels of the oscilloscope and enables the user to perform logical operations on the signals from the two channels to produce the oscilloscope trigger. The four logical functions of AND, OR, NAND, and NOR are supported as well as the ability to specify time values for the duration of the logical condition.

An extremely useful and powerful feature of the Siglent SDS series oscilloscopes is the ability to decode a variety of serial bus signals commonly used in modern electronic circuitry. The Inter_IC bus (I2C) serial format may be decoded and displayed as well as the ability to trigger on specific serial bus signals such as the start/stop condition, restart signal, missing ACK, data read, or even a specific device address, data value, or data length.


The Serial Peripheral Interface (SPI) bus may also be effectively troubleshot using this unit. The setup is similar to the I2C, but with obvious changes due to the differences of the characteristics of this bus. The triggering can be set to various framing signals based on Chip Select (CS) and Clock Timeout periods. Additionally the Idle Level may be selected as either High or Low and the Bit order may be specified as either MSB or LSB to accommodate all possible variations allowable with this serial bus type. The data length and even a specific data word value may be used to start the data acquisition process.

UART and RS232 signals can be quite difficult to troubleshoot due the asynchronous nature of this bus. The Siglent SDS series oscilloscopes can make this process less daunting by providing an easy-to-use interface for viewing and decoding UART signals. The user has the ability to select Baud rate, Parity, number of Stop bits, and data length. A specific data value may be used to begin the data acquisition cycle that can be most effective when receiving long data streams.

Controller Area Network (CAN) bus and the Local Interconnect Network (LIN) bus are used extensively in modern automobile electronic systems. The CAN bus can provide for baud rates between 5 Kb/s up to 1 Mb/s. The trigger condition can then be set to Start, Remote, ID bits, ID+Data, or Error. The data displayed consists of the frame number, type of frame, frame ID, data length, the decoded data, the CRC value, and the ACK signal.

The Local Interconnect Network (LIN) bus is a lower cost alternative to the CAN bus and is used for less demanding, lower bandwidth applications. Baud rates can range from 1 b/s up to 20 Kb/s. Data displayed is Frame ID, decoded data, length of data, ID parity check, and data error check.

The Siglent SDS series digital storage oscilloscopes provide powerful triggering and decoding features for use with modern serial buses. These advanced features can save many hours of engineering development and debugging time at a relatively low initial investment cost.


George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

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