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Keysight Technologies
FlexRay Physical Layer
Eye-diagram Mask Testing
Application Note
Introduction
Eye-diagram mask testing is one of the most important physical layer measurements that you can use
to test the overall signal integrity of your FlexRay system. Keysight Technologies, Inc. provides seven
different FlexRay mask files based on FlexRay physical layer standards/specifications for use with
InfiniiVision 3000X, 4000X, 6000X, 6000, and 7000 Series oscilloscopes (DSO or MSO) from
Keysight. Which particular mask file you use is determined by the baud rate of your system, the test
plane where testing will be performed (receiver input or transmitter output), and the type of output
device that may be under test (Bus Driver or Active Star).
Eye-diagram testing is used in a broad range of today's higher speed serial bus applications including
FlexRay. An eye-diagram is basically an overlay of digitized bits that shows when bits are valid (high
or low). This provides a composite picture of the quality of a system's physical layer characteristics,
which includes amplitude variations due to transmission line affects, reflections, over-shoot, ringing,
signal edge placement, and jitter.
Keysight scopes are the only scopes that can perform hardware-based FlexRay eye-diagram mask
testing. With hardware-based mask testing, up to 200,000 waveforms can be tested per second.
This enables you to test more bits faster to insure reliable operation of your FlexRay system.
This application note will first provide you with an overview of the various types of FlexRay eye-
diagram mask testing that can be performed. We will then provide you with simple step-by-step
instructions on how to set up eye-diagram mask tests on a Keysight InfiniiVision series oscilloscope.
03 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
A basic understanding of FlexRay eye-diagram mask testing
Using FlexRay mask test files only requires that your
InfiniiVision series scope be equipped with the latest
FlexRay option as well as the Mask Test option. The
following FlexRay mask test files are available to download
from Keysight's website at no charge.
FlexRay 10Mbs TP4 Mask.msk
FlexRay 5Mbs TP4 Mask.msk
FlexRay 2,5Mbs TP4 Mask.msk Figure 1: TP4 mask test setup.
FlexRay 10Mbs TP1 Mask.msk
FlexRay 10Mbs TP1-Incr V Mask.msk
FlexRay 10Mbs TP11 Mask.msk
FlexRay 10Mbs TP11-Incr V Mask.msk
Receiver Input Mask Testing
The three different TP4 mask files are for testing signals at
the input of any FlexRay receiver. You should select the one
that matches the baud rate of your FlexRay system.
TP4 mask testing is the most common eye-diagram mask
test for evaluating the overall quality of your synchronous
multi-node FlexRay system.
The scope's differential probe should be connected as close
as possible to the BP and BM inputs of the receiving node
that is under test as shown in Figure 1. To test all receiving
nodes in the system, multiple TP4 mask tests must be
Figure 2: FlexRay 10Mbs TP4 mask test on "all" frames at the receiver input
performed with the probe re-connected to each receiving of a specific node.
node's BP and BM test points.
Figure 2 shows an example of a FlexRay eye-diagram mask
test based on a TP4-10 Mbps standard. The triggering
reference for the TP4 mask test is each Byte Start Sequence
(BSS) event. This is the same reference signal that FlexRay
receivers use to re-synchronize and recover clocks for
sampling received data. The Keysight InfiniiVision series
oscilloscopes utilize a unique repetitive hardware clock
recovery technique to capture and overlay each bit of every
byte in the system. We will discuss later how you can "filter"
testing on specific frame IDs.
04 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
A basic understanding of FlexRay eye-diagram mask testing (continued)
Transmitter Output Mask Testing
The TP1 mask files are for testing the output of either a
standard-voltage or increased-voltage Bus Driver (BD)
device. The TP11 mask files are for testing the output of
either a standard-voltage or increased-voltage Active Star
(AS) device.
The differential output characteristics of these devices
should be tested using a pulse/pattern generator as a Figure 3: TP1 and TP11 mask test setup.
source that drives the single-ended inputs of the device
under test. The generator should be setup to output a
continuous 1-0-1-0... serial pattern at 10 Mbs (5 MHz square
wave) with a near-perfect 100 ns bit time and gated by
TxEn-low as shown in Figure 3.
The output of the device under test (bus driver or active
star) should be terminated with a 40- resistor in parallel
with a 100-pF capacitor across BP (bus plus output) and BM
(bus minus output). The scope's differential probe should be
connected to BP and BM as close as possible to the output
of the device under test.
Figure 4 shows an example of a FlexRay mask test based on
a "TP1-Standard V" mask file. TP1 and TP11 mask tests are
based on the scope triggering on alternate rising and falling
edges of the output differential signal.
Note that 5Mbs and 2.5 Mbs masks do not exist for testing Figure 4: TP1-Std V mask test at the output of a Bus Driver device.
the output characteristics of bus drivers and active stars at
TP1 and TP11. Even if these devices will be used in 5 Mbs
or 2.5 Mbs FlexRay systems, they should be tested to the
10Mbs standard.
Although the TP1 and TP11 mask files are intended for will actually consist of both transmitted and received signals
testing output devices using a signal/pattern generator as (signals generated from the "buddy" node). If the test
the device input source, these mask files can also be used passes when testing signals generated by both nodes, then
to test actual 10 Mbs FlexRay output traffic generated by you can be confident that the output characteristics of the
a FlexRay Communication Controller within "closed" ECU particular transmitting node that is under test meets required
systems. However, it is critical that the network under output device specifications. But if the test fails, then this
test be carefully controlled and the test results should be could be due to testing the "received" signals from the
carefully interpreted. "buddy" node. There is no way to isolate TP1 and TP11 eye-
diagram testing on particular frame IDs as there is with TP4
eye-diagram mask testing (receiver input testing).
To test the output characteristics of a particular node within
a synchronous system, such as a single ECU along with a
second "buddy" node, first of all make sure that the length You should be cautioned to never test an actual in-car multi-
of the transmission line network is minimized and is tightly node system consisting of a long and complex transmission
controlled. Secondly, be aware that the results of a TP1 or line network (or a simulated in-car network) using either the
TP11 eye-diagram mask test on this type of 2-node system TP1 or TP11 eye-diagram mask files.
05 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
Step-by-step instructions on how to begin executing a FlexRay
eye-diagram mask test
After downloading, unzipping, and storing the various
FlexRay eye-diagram mask files onto a USB memory
stick, insert the memory stick into the scope's USB
port on the scope's front panel and then follow these
simple steps:
1. Turn OFF all channels of the oscilloscope except for
the channel that the differential probe is connected
to. If you plan to use channel-1, it is recommended
that you begin by pressing the [Default Setup] front
panel key.
2. Press the [Save/Recall] front panel key.
3. Press the Recall menu softkey.
4. Press the Recall: XXX softkey (left-most menu key),
and then select Mask as the file type to recall
using the selection knob.
5. Press the Location softkey key, and then select the
specific mask file to recall from the "/usb0"
drive using the selection knob (shown in Figure 5).
6. Press the Press to Recall softkey.
When the mask file is loaded, in addition to recalling
the pass/fail mask, the scope automatically detects
which channel of the scope is turned on, sets the probe
attenuation factor and input coupling, optimizes the
V/div setting, sets the trigger level, and sets up the
timebase to display two bits centered on-screen. In
addition, the scope will perform a one-time time-skew
calibration in order to place the mask in its proper
location relative to the trigger event. The scope will
then begin running the mask test sequence.
When the mask test sequence is running repetitively,
you cannot change the scope's timebase settings
(s/div and delay). Although you have the ability to
re-scale the vertical settings of the scope after the
mask test sequence begins, after making any vertical
scale changes (V/div and/or offset) or trigger level
changes, you should press the [Run/Stop] front panel
key two times. The first time you press the [Run/
Stop] key, mask testing will pause. The second time
you press the [Run/Stop] key, the scope will perform
a new time-skew calibration based on the new vertical
and trigger level settings, and then begin repetitive
mask testing again. Figure 5. Recalling a FlexRay eye-diagram mask test file.
To exit a FlexRay mask test sequence, select either
Clear Mask or Mask Test = OFF in the mask test
menu. The scope will then restore most setup
conditions to the state they were in prior to beginning
the FlexRay eye-diagram mask test
06 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
Performing FlexRay Eye-diagram Mask Tests on Specific Frame IDs
The TP4 mask files provided by Keysight will capture and
perform mask testing on all bits of all bytes of all frames in the
system. But in order to isolate signal integrity issues down
to specific transmitting nodes, it may be desirable to perform
TP4 mask testing on user-specified frame IDs. If you are using
a Keysight 3000, 4000 or 6000 X-Series oscilloscope, select
the scope's [Trigger] front panel key, and then change from
triggering on BSS events from All frames to a specific frame
ID value.
If you are using a Keysight 7000 Series oscilloscope, Figure 6: Editing a TP4 mask file in order to test specific frame IDs.
triggering on BSS events can be accomplished by editing a
single parameter within the TP4 mask file on your PC using Note that it is not generally necessary to test every frame ID
a standard text editor, such as Windows NotePad. First, generated by each node. The purpose of TP4 mask testing is
open the TP4 mask file using a common text editor on your to test the quality of signals generated from a specific node
PC. Then scroll down to the second to last line of this text over the FlexRay network. Signals of different frame IDs that
file (Figure 6) and modify the "ALL" text that is within the are generated from the same node (same transmitter) will all
mask test sequence SCPI command (:MTES:TSEQ:FLEX:TP4 have similar analog signal quality characteristics, which are
1000000, ALL) to the frame ID number (decimal format) that usually determined by the network; not the specific frame ID
you want to test. In other words, if you want to perform an or transmitter. For this reason it is usually only necessary to
eye-diagram mask test on just frame ID:33, then change test one frame ID from each transmitting node in the system
"ALL" to "33" (:MTES:TSEQ:FLEX:TP4 1000000, 33). in order the test the network from a specific transmitter to a
specific receiver test plane.
Note that although not required, you may also want to modify
the "mask test label" in this file in order to indicate which Figure 7a shows an example of testing a multi-node
frame is being tested. The "mask test label" is specified on synchronous FlexRay system at a specific receiver's TP4
the 2nd line near the top of this text file. The default label is, input test plane using the mask file's default "all" mask test
"FlexRay 10-Mbs TP4". This label will appear in the scope's sequence command. From this test we can see that various
mask test menu after the file in recalled. transmitting nodes are generating signals that exhibit different
characteristics at our particular TP4 test plane. And we can
When you have finished editing the TP4 mask file, save also see that one or more transmitting nodes are producing
this file as a text file using a ".msk" extension. It is also mask violations due to insufficient signal amplitude. When
recommended to give this edited mask file a new file name testing the entire system (all frames), the mask failure rate is
in order to preserve the original "all" mask test file. Next, approximately 0.5%.
re-insert your memory stick into the scope's USB front-panel
port and recall this edited mask file to begin performing TP4 Figure 7b shows a mask test at the same input test plane, but
mask testing on a specific frame ID. the mask file was edited in order to test just frame ID:13. Now
we can see that the mask failure rate is over 30% and we have
isolated our mask testing down to the troublesome transmitting
node and its associated transmission line network.
Figure 7a. TP4 mask test on ALL frames. Figure 7b. TP4 mask test on frame ID:13.
07 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
System Requirements
To perform FlexRay eye-diagram mask testing on a 3000, 4000 with the FlexRay triggering and decode option (Option FLX
or 6000 X-Series oscilloscope, your scope must be licensed or N5432C). Although the mask test option is also required,
with the FlexRay triggering and decode option (DSOX3FLEX, this option (Option LMT) comes standard with the FlexRay
DSOX4FLEX or DSOX6FLEX), as well as the mask test option option. In addition, your 6000 or 7000 Series oscilloscope
(DSOX3MASK, DSOX4MASK or DSOX6MASK). In addition, must be running on firmware revision 6.0 or later. If your
your 3000 X-Series oscilloscope must be running on firmware 6000 or 7000 Series oscilloscope is licensed with a previous
revision 2.0 or later. version of the FlexRay option (Option FRS) that utilizes the
VPT1000 FlexRay acquisition module, contact Keysight about
To perform FlexRay eye-diagram mask testing on a 6000 upgrading to the latest FlexRay option (Option FLX).
or 7000 Series oscilloscope, your scope must be licensed
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08 | Keysight | FlexRay Physical Layer Eye-diagram Mask Testing - Application Note
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