Teledyne LeCroy Line Code and Symbolic Decoders - Manual (Page 5)

Instruction Manual
922663 Rev A 3
NOTE: 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 Teledyne LeCroy software algorithm.
After determining individual data bit values, another algorithm performs a decoding of the serial data
message after separation of the underlying data bits into logical groups (Header/ID, Data Length Codes,
Data, CRC, Start Bits, Stop Bits, etc.) specific to the protocol.
Finally, another algorithm applies a color overlay to the decoded trace with annotations to mark the
transitions in the signal and displays decoded message data in tabular form. 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.
General Approach
The order of your interaction with the decoder software in many ways mirrors the order of the
algorithms. You will:

Assign a protocol/encoding scheme, an input source, and a clock source (if necessary) to one of
the four decoder panels using the Serial Data and Decode Setup dialogs.

Complete the remaining dialogs required by your protocol/encoding scheme to decode
Transitions, Bits and Words.

Work with the decoded waveform and result table to analyze the decode.
While not required, we recommend the following general approach to decoding:
1. Set up the decoder.
2. Acquire a single burst of relevant data, then run the decoder.
NOTE: If the sampling rate (SR) is insufficient to resolve the signal adequately based on the bit rate
(BR) setup or clock frequency, the protocol decoding is turned OFF to protect you from incorrect
data. The minimum SR:BR ratio required is 4:1. It is suggested that you use a slightly higher SR:BR
ratio if possible, and use significantly higher SR:BR ratios if you want to also view perturbations or
other anomalies on your serial data analog signal.
3. Use the various analysis tools to verify that transitions are being correctly decoded. Tune the
decoder settings as needed.
4. Once you know you are correctly decoding transitions, continue making small acquisitions and
running the decoder for bits then words in turn, tuning the decoder as needed for each.
The decoder settings you verify on a few bursts will be reused when handling many packets.
5. Run the decoder on acquisitions of the desired length.
You can disable/enable the decoder as desired without having to repeat the set up and tuning
provided the basic signal characteristics do not change.