Do you know about FlexChannel for multi-bus system debugging?

Do you know FlexChannel for debugging multi-bus systems? What does it do? Most embedded systems adopt a multi-bus structure. In order to observe these systems, debugging and verification tools must be able to display the activities of multiple buses, as well as sensors and actuators. , display and interface signals. The challenge is not only looking at multiple buses, but each bus requires a different signaling method and therefore a different probing method. Some buses can be observed using single-ended measurements, others require differential measurements. In order to view multiple buses, you may want to leverage digital logic channels, greatly expanding the number of channels.

New FlexChannel input channels allow the widest range of probes to be used to measure multiple different signals. Each FlexChannel can measure:

ŸMeasuring a single-ended analog signal using a passive probe

ŸUse TLP058 logic probe to connect to 8 digital channels and measure 8 digital logic signals.

ŸUse TekVPI® differential voltage probe to measure a differential voltage signal.

ŸUse IsoVuTM isolation measurement system to measure an optically isolated differential voltage signal

ŸMeasure 1 current signal using TekVPI® current probe

FlexChannel technology on Tektronix's new 4 Series MSO oscilloscopes allows each channel input to be used as an analog channel or as 8 digital logic inputs (using the TLP058 logic probe), or simultaneously with analog and spectrum views, with independent Collection control can be flexibly configured according to needs. To capture high-fidelity bus signals, several factors need to be considered.

Acquire single-ended bus signals

Many commonly used low- and medium-speed buses use single-ended signaling, representing digital signals at a specific voltage relative to system ground. These analog signals are typically captured using passive voltage probes that come standard with the oscilloscope or using digital probes on a mixed-signal oscilloscope. The FlexChannel input supports both probe types, some important factors to consider include:

ŸThe ground wire should be as short as possible. In order to successfully acquire analog signals, first ensure that each channel's reference voltage is connected to the oscilloscope through a low-inductance path.

Ÿ Ensure that the rise time of the measurement system is less than one-fifth of the signal rise time. The performance of the oscilloscope and probe must provide an adequate and realistic representation of the signal. A common guideline is to ensure that the bandwidth of the measurement system is at least five times the signal bandwidth and the sampling rate is at least 3-5 times the signal bandwidth.

ŸFor digital logic circuits on the MSO, the combined system bandwidth of the oscilloscope and probe should be sufficient to capture the signal, and the sampling rate on the digital channel should be at least 10 times the signal frequency. Performance is usually expressed in terms of bandwidth or the minimum pulse width that can be detected.

ŸEnsure that the probe impedance is large relative to the signal source impedance to minimize the impact of probe loading on the signal.

ŸFor low-power circuits, this is mainly the input resistance of the probe; for high-speed signals, this is mainly the input capacitance of the probe.

Acquire differential bus signals

To improve the bus's immunity to noise, and to improve the signal integrity of higher-speed buses, differential signaling is often used. Unlike single-ended signaling, differential signaling is represented by the voltage difference between two signals. For some low-frequency applications, single-ended probes can be used to capture each side of the differential signal, and the oscilloscope can calculate the mathematical difference. In practice, this technique is particularly prone to errors due to differences in probe gain, propagation delays, and compensation. The most reliable way to capture differential signals is to use an active differential probe, which uses a differential amplifier at the probe tip to sense voltage differences.

The performance considerations listed above for single-ended probes also apply to digital probes. However, it is important to note that differential probes have the ability to ignore or reject common-mode signals. A primary specification for these probes is the common-mode rejection ratio (CMRR) at the frequency of interest. Tektronix offers a variety of differential probes with varying capabilities, including the optically isolated IsoVuTM differential measurement system designed for the most demanding measurement environments.

For all signaling methods - thresholds are key

Regardless of the technique used to capture the signal, an analog representation of the bus signal is typically connected to an oscilloscope. Before the bus signal can be correctly interpreted, the analog signal must be compared with a threshold. If it exceeds the threshold, it is generally interpreted as high ("1"); if it is below the threshold, it is generally interpreted as ("0"). (In some cases, the analog voltage is compared to a threshold inside the digital logic probe.)

Many embedded designs are based on multiple logic families, requiring the use of various numerical thresholds. Some oscilloscopes support setting dedicated thresholds for each channel to achieve maximum debugging flexibility and acquisition fidelity.

Isolating Signal Integrity Issues Using Waveform Trigger Mode

When debugging signal integrity issues on a parallel or serial bus, the first step is to capture signals that violate design specifications using the standard trigger modes in advanced oscilloscopes:

ŸPulse width triggering can be used to isolate glitches and minimum pulse width violations on clock and data lines.

ŸYou can use timeout triggering to isolate missed pulses, such as in clock signals.

ŸYou can use rise time and fall time triggering to isolate signal edges that are too fast or too slow in your design.

ŸYou can use runt pulse and window triggering to isolate digital signals with incorrect, too low, or too high amplitudes.

ŸMulti-channel setup and hold time triggering function compares the timing of one or more data signals with a clock signal to detect component setup and hold time violations.

Embedded system design is becoming more and more complex, and more and more types of signals are integrated. Once any signal integrity issues have been resolved, the next step is to verify that the wider system is working as expected. The new series of MSO provides the best tools for debugging and testing multi-bus systems. It uses a 15.6-inch ultra-large high-definition display with twice the display area of ​​a 10.4-inch display. The high-definition resolution can support multiple signals and buses. The above is the FlexChannel analysis for debugging multi-bus systems. I hope it can help you.