Teledyne LeCroy ENETbusD Decoder - Manual (Page 5)

Instruction Manual
922665 Rev A 3
Serial Decode Technical Overview
The algorithms described here at a high level are used by all Teledyne LeCroy serial decoders sold for
oscilloscopes. They differ slightly for serial data signals that have a clock embedded in data or a clock
separate from data.
The first software algorithm examines the embedded clock for each message based on a default (or user
specified) vertical level. Once the clock signal is extracted or known, the algorithm examines the
corresponding data signal at a predetermined vertical level to determine whether a data bit is high or
low. The default vertical 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. The algorithm intelligently applies a hysteresis to the rising and falling edge of the serial data
signal to minimize the chance of perturbations or ringing on the edge affecting the data bit decoding.
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.
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 with annotations to the decoded waveform to mark
the transitions in the signal. Decoded message data is displayed in tabular form below the grid. 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.