Oscilloscope Serial Data Measurements and DAC: Trigger, Decode, Measure/Graph and Eye Diagram Software

Figure 1. Serial bus measurements made available
with "TDME" and "TDMP "decoder options.

All Teledyne LeCroy oscilloscopes support a rich set of standard waveform measurement parameters, but the installation of any "TDME" or "TDMP" serial decoder software option adds special parameters designed for measuring serial data buses. Besides automating the measurement of serial bus timing, these parameters allow you to access encoded serial data and extract it to analog values for what is essentially a Digital-to-Analog Converter (DAC)!

What’s in a Name?

Teledyne LeCroy has adopted the convention of using a key in the name of our serial trigger and decode products that tells you what capabilities they offer.  The “ME” or “MP” in the name of a Teledyne LeCroy serial decoder option (e.g., CAN FDbus TDME or USB4-SB TDMP) refers to "Measure/Graph and Eye Diagram" or "Measure/Graph and Physical Layer Tests." All these options include the following 10 serial bus measurements. Physical Layer Test options will also include measurements designed specifically to meet the requirements of the standard.

Physical-Layer Collision Avoidance in 10Base-T1S Automotive Ethernet

Fig.1, 10Base-T1S PLCA cycle. If there is no data
traffic (top), only BEACONs are seen on the bus. 
Data from a node (bottom) will expand the time
between two BEACONs.

10Base-T1S (IEEE 802.cg) is a variant of Automotive Ethernet  that supports half-duplex and full-duplex communication, allowing either a point-to-point direct connection between two nodes, or use of a multidrop topology with up-to-eight nodes connected on a single 25 m bus segment.

Multidrop cabling of one bus line provides options to extend and scale with fewer physical wires and less weight than point-to-point topologies. With minimum connector space at the ECU, the bus line can be expanded simply by adding sensor units. A bus line with additional sensor units for ultrasonic and short-range radar is an example of how multidrop cabling can be scaled.  

Among the main objectives of the 10Base-T1S PHY layer are reconciliation of transmissions from a variety of mediums, ensuring cooperative behavior by the nodes on a multidrop bus. One way it does this is through the use of Physical-Layer Collision Avoidance (PLCA) technology to minimize dead time and avoid collisions. In this post, we'll describe the workings of PLCA and in a future post, how you can debug PLCA timing issues using an oscilloscope with the 10Base-T1S TDME software.

Correlating Sensor and Serial Data in Complex Embedded Systems

Figure 1: Voltage output of a temperature sensor.
As the temperature rises, the output voltage falls. 

The microcontrollers/microprocessors in deeply embedded systems often are set up to monitor and control operational parameters.  Take, for example, a deeply embedded system where a microcontroller is used to control temperature that has been sensed by a temperature sensor.  The sensor is read through one of the microcontrollers analog interfaces.  As temperature changes are sensed, the microcontroller adjusts the speed of a cooling fan, which is driven by a pulse width modulated signal. The microcontroller uses a program algorithm to convert the DC level of the sensor into a PWM signal with an appropriate duty cycle to set the fan speed to correct any changes in temperature. 

Where it is possible to probe the temperature sensor, the output is a DC signal that changes very slowly over time.  Figure 1 shows a direct measurement of the temperature sensor using a heavily filtered oscilloscope channel to minimize noise pickup.

TDME Primer: Automated Timing Measurements of USB-C Protocols

Figure 1: Interleaved decoding of USB-PD and DP-AUX signals.

Increasingly, serial data analysis is analysis of the interoperability of the many protocols that must perform together within interconnects and embedded systems. Nowhere is this more true than for USB-C® devices, which we’ll focus on in this post, although these examples of cross-protocol timing measurements could apply to any two protocols supported by our TDME and DME options.

The USB-C connector packs many protocols onto one, small pin set, and maintaining signal and power integrity is a compliance challenge. Besides high-speed data delivery, USB-PD (power delivery) provides flexible power distribution, while auxiliary sideband signals, like DisplayPort™, transport video. Troubleshooting these capabilities requires the ability to measure timing between serial data packets, as well as between data packets and analog signals. 

For example, DisplayPort over USB-C (DPoC) in alternate mode (alt-mode) can manifest as an interoperability failure if there is a timing issue between alt-mode initiation and the start of DP-AUX.

Debugging Low-Speed Serial Data on IoT Devices

Figure 1: Serial-data links handle traffic between ICs
and peripheral devices in the IoT world

Our last post discussed the difficulties in acquiring the many sensor signals that may be input to a deeply embedded system such as an IoT device as well as a hardware solution to the problem. Another aspect of IoT debugging and validation is the low-speed serial data standards used to facilitate communication between ICs and between controllers and peripheral devices (Figure 1). To that end, let's take a look at three such low-speed standards: I2C, SPI, and UART.

Getting The Most Out Of Your Oscilloscope: Physical-Layer Tools

Figure 1: Trigger dialog boxes will
match the protocol of interest

Debugging and validation of the physical layer of serial-data links is a preeminent oscilloscope application area these days. Today's real-time digital oscilloscopes have a wealth of tools to help you dig into any/all serial protocols and learn what's really going on electrically with your serial links.

The Periodic Table of Oscilloscope Tools: Analyze (Part II)

Figure 1: The Analysis
tools in an oscilloscope
lend it debug power

Oscilloscopes are central to many engineering tasks, but perhaps to none more so than debugging. Something is going on with your design but you don't know what it is. However, armed with an oscilloscope with the sort of sophisticated analysis tools found in Teledyne LeCroy's instruments, even Mr. Jones can get to the bottom of the problem. Let's continue our survey of the Periodic Table of Oscilloscope Tools with more on analysis tools.