Front cover of the BroadR-Reach automotive Ethernet specifications.

BroadR-Reach 100BASE-T1 decoder / analyzer

BroadR-Reach (IEEE 802.3 100BASE-T1) is an Ethernet physical layer standard designed for use in automotive networking applications. BroadR-Reach technology allows multiple in-vehicle systems to simultaneously access information over low-cost unshielded single twisted-pair cable. BroadR-Reach delivers relatively high-speed data, 100 Mbps, with low connectivity costs and cabling weight.

BroadR-Reach physical layer 'BR-PHY' uses three-level pulse amplitude modulation (PAM3) signaling and operates as a full-duplex connection (simultaneous Master-Slave / Slave-Master transmissions).

Transmission bandwidth is limited to 33⅓ MHz to meet Automotive Electromagnetic Compatibility requirements, according to CISPR 25 test methods for RF immunity and emissions. Furthermore, a data scrambling technique is employed to randomize the sequence of transmitted symbols to even out the power spectral density.

PicoScope* can separate the bidirectional Master-Slave and Slave-Master interfering waveforms with a non-intrusive Software Directional Coupler, and can decode and analyze the resulting waveforms to display packets in both directions.

Video: Automotive Ethernet - Decoding & Analysis with PicoScope

* Directional coupler and decoder are included with PicoScope release 6.14.10 or later.

100BASE-T1 waveforms captured at test points two metres apart, close to the Master and Slave devices respectively.

100BASE-T1 full duplex waveforms.

Full-duplex signaling

BroadR-Reach physical layer "BR-PHY" uses three-level pulse amplitude modulation (PAM3) signaling and operates as a full-duplex connection (simultaneous Master-Slave / Slave-Master transmissions) using a differential pair of wires.

Where signals are being transmitting in opposite directions simultaneously they interfere with each other and must be separated into upstream and downstream waveforms in order to be decoded.

A hardware directional coupler can be used for the job, but it has several drawbacks; mainly that it is an "intrusive" device that has to be inserted in the network and can interfere with the very signals being tested.

Software Directional Coupler

The PicoScope BroadR-Reach decoder / analyzer includes an innovative non-intrusive Software Directional Coupler math channel function that utilizes two probing points a known distance apart, and a velocity of propagation algorithm to separate the transmitted data waveforms in each direction.

Velocity of Propagation (VOP) is a specification that describes the speed of a signal down a given cable relative to the speed of light in a vacuum (3.0 x 108 m/s). The VOP of a Cat 5 twisted-pair Ethernet cable is around 0.66. This means that a signal will travel down a Cat 5 cable at a speed of 0.66 x 3.0 x 108m/s ≈ 2 x 108 m/s.

PicoScope software directional coupler - setup panel

Software Directional Coupler - Settings

The Software Directional Coupler outputs the waveform that is being transmitted from the first to the second test point. (Make sure they are set up in the correct order in the software directional coupler.)

Use the Zoom control to expand the trace to observe the characteristic three-level PAM3 waveform.

Use horizontal rulers set at the specified PAM3 threshold voltages (typically +1, –1 V) for initial inspection of the waveform integrity.

BroadR-Reach Master to Slave directional waveform; output from the PicoScope software directional coupler.

BroadR-Reach decoder

To decode a BroadR-Reach waveform in PicoScope, go to the Tools menu and select Serial Decoding.

PicoScope Tools menu, with Serial Decoding shown selected.

PicoScope Serial Decoders menu, with BroadR-Reach highlighted.

PicoScope BroadR-Reach decoder settings panel.

In the BroadR-Reach Settings menu choose the differential signal that you want to analyze.

If using the PicoScope Software Directional Coupler described above, select that Math channel.

Set the High and Low Thresholds to match the PAM3 waveform standard, typically +1 V and –1 V.

Tick Master to identify Master > Slave data transmission, matched to the direction of the signal that you selected in the software directional coupler. Left unticked, the decoder will be set for Slave > Master decoding.

(The decoder needs to know the transmission direction because Master uses slightly different parameters for the scrambling algorithm than the Slave.)

Decoded waveform in graph

The decoder displays the decoded data in a ribbon underneath the Master > Slave directional waveform.

100BASE-T1 decoded waveform on PicoScope

Decoded data in table

The decoded data can be displayed in tabular listing format for ease of viewing.

Doubleclicking a particular frame takes you to the same frame in the graph display.

For convenience you can place the table on a second display monitor, if you have one available.

PicoScope BroadR-Reach data decoded in tabular format.

View fields

You can choose which fields to display in the table.

PicoScope BroadR-Reach field selector for table view.

Filter on field values

Use the Filter button and enter the field data to filter on in the column heading(s).

Example of filtering on field data values in the PicoScope BroadR-Reach decoder.

Search on field values

Use the Search function and enter the search field plus search data to find frames of interest.

Use the Forward and Backward buttons to find further instances.

PicoScope BroadR-Reach decoder, search function setup.

TA045 200 MHz differential voltage probe for probing high frequency differential signals such as 100BASE-T1 Ethernet.

Hardware requirements for a complete BroadR-Reach solution on PicoScope

The BroadR-Reach decoder / analyzer, including the Software Directional Coupler, is included as standard with PicoScope software version 6.14.10 and later. So, if you already have the right PicoScope hardware (see below) it’s free of charge! The required hardware is:

PicoScope 6000 – any model. With bandwidths from 250 to 500 MHz, 5 GS/s sampling and capture memory up to 2 gigasamples.

TA045 200 MHz differential probes (x2) for probing the two test points on the BroadR-Reach network.

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