LeCroy DDA 7 Zi series, Operator'S Manual

Page: 209 / 544

Operator's Manual
WP700Zi-OM-E-RevA
208
Decode
Protocol
Selections As serial decode options are added to your oscilloscope,
additional protocol selections are available in a pop-up menu
within the Decode Setup dialog box.
Technical Overview
LeCroy’s offering of serial trigger and decode options utilize advanced trigger circuitry and advanced software
algorithms to provide powerful capability for serial data triggering and decoding.
Serial Trigger
TD options contain advanced serial data triggering. This serial data triggering is implemented directly within the
hardware of the oscilloscope acquisition system, and contains advanced algorithms to protocol decode,
recognize, and trigger on user-defined serial data patterns. This allows a recognized serial data pattern to be
used to trigger the oscilloscope at a pre-determined time, and other signals coincident with the desired serial data
pattern can be captured simultaneously.
Serial Decode
Both the D and TD options contain powerful protocol decoding and annotation software algorithms. This algorithm
is used in all LeCroy serial decoders sold with oscilloscopes, and differs slightly for serial data signals that have a
clock embedded in data or a clock separate from data.
The software algorithm examines the embedded clock (CAN) or separate clock line (I
2
C, SPI) for each message
based on a default (or user set) vertical level. The algorithm is intelligent in that it applies a hysteresis to the rising
and falling edge of the serial data signal to minimize the chance that perturbations or ringing on the edge will
affect the decoding. The default level is usually set to 50% and is determined from a measurement of peak
amplitude of the signals acquired by the oscilloscope. It can also be set to an (absolute) voltage level, if desired.
For serial data signals with embedded clocks (i.e., CAN), the algorithm then performs an analysis of the serial
data message to determine the nominal bit width. The clock rate/bit width is measured directly from the clock line
for other serial data formats (i.e., I
2
C and SPI). Once the clock signal is acquired and the decoding is completed
for a serial data message with separate clock and data lines, the oscilloscope channel can be turned OFF to
reduce screen clutter.
After determining bit width, a different algorithm performs a decoding of the serial data message into binary format
after separation of the underlying data into logical groups (Header/ID, Data Length Codes, Data, CRC, Start Bits,
Stop Bits, etc.). Finally, another algorithm provides the appropriate color coding of the message, and displays the
protocol message data on the screen, as desired, overlaid on the source trace. Various compaction schemes are
utilized to show the data during a long acquisition (many hundreds or thousands of serial data messages) or a
short acquisition (one serial data message acquisition). In the case of the longest acquisition, only the most
important information is highlighted. In the case of the shortest acquisition, all information is displayed (Header/ID,
Data Length Codes, Data, CRC, Start Bits, Stop Bits, etc.) with additional highlighting of the complete message
frame.
Note that although the decoding algorithm is based on a clock extraction software algorithm using a vertical level,
the results returned are the same as those from a traditional protocol analyzer using sampling point-based
decode. In addition, the clock extraction technique allows partial decoding of messages in the event of physical
layer noise, in many cases, whereas a protocol analyzer usually cannot. This is a significant advantage for the
LeCroy software algorithm.