For UART Debugging, Triggering is Key

Figure 1: A typical screen capture of UART
serial decode/trigger software

In our survey of how modern oscilloscopes and trigger/decode software (Figure 1) can ease the task of debugging embedded systems, we've covered the I²C and SPI protocols. Now we'll turn to the UART format, where triggering capabilities are of particular importance.

Shaking Bugs Out of SPI Buses

Figure 1: Debugging of SPI on a Teledyne LeCroy
WaveSurfer 3000 oscilloscope

In the first post of this series, we considered some of the challenges of debugging embedded systems in general and I²C buses in particular. Modern digital oscilloscopes equipped with powerful trigger/decode software for the serial protocol in play go a long way toward easing the path to a properly functioning embedded system. Now we'll consider the particularities of the Serial Peripheral Interface and how the proper tools can make debugging SPI buses easier.

Test Challenges for PAM4 Signals

The major test challenges posed by PAM4 signals

PAM4 encoding offers the advantage of doubling the bit rate in a serial data channel, doing so by increasing the number of voltage levels from two to four. It's a fairly complex modulation scheme, so it should be no surprise that it presents some test and measurement challenges.

Why High Oscilloscope Sampling Rates Matter

Figure 1: Here is an example of aliasing that results from
sampling a signal at less than the Nyquist rate of 2f_max

A key to accurate measurements with an oscilloscope is to ensure that the instrument maintains a high sampling rate. This applies to most measurements; conversely, for many measurements, accuracy may suffer as sample rate decreases. In the worst case, some signal components may be "aliased," meaning that the true signal shape is corrupted by the addition of bogus signal components that arise from undersampling of real signal components.

Debugging I2C Buses in Embedded Systems

Figure 1: Debugging of I²C on a Teledyne LeCroy
WaveSurfer 3000 oscilloscope

Embedded systems became ubiquitous decades ago and are now found in everything from mobile devices to vehicles to the traffic lights that control their movements. These days, they're typically based on microcontrollers and perform some specific task(s) within a larger system, such as controlling your car's ABS system. They may or may not have any sort of user interface, and can range widely in terms of complexity and functionality.

PAM4 Test Setups Vary With Applications

Figure 1: A high-level view of PAM4 use cases

In an earlier post, we surveyed the basic properties of PAM4 signals. Now, we will examine some of the ways in which PAM4 is finding application in the real world and what test and measurement setups might look like for those applications.

The Fundamentals of PAM4

PAM4 doubles the number of bits in serial data transmissions
by increasing the number of levels of pulse-amplitude modulation,
but does so at the cost of noise susceptibility

As our society's hunger for data grows—not only more data, but more data delivered faster—older modulation schemes based on NRZ-type encoding grow increasingly inadequate. We need to get data from point A to point B as efficiently as possible, whether that means between chips on a PC board or from one end of a long-haul optical fiber to the other. A modulation scheme that's gaining favor in many quarters is PAM4, and in this post we'll look at the basics of PAM4 before turning to the test and analysis challenges it poses.