USB-PD TDMP Instruction Manual
Serial Decode
The methods described here at a high level are used by all Teledyne LeCroy serial decoders, differing only slightly for
signals with an embedded clock and separate clock and data signals.
Bit-level Decoding
The first software algorithm examines the embedded clock based on a default or user- specified vertical threshold
level. Once the clock signal is extracted, the algorithm examines the traffic to determine whether a data bit is high or
low. The default High and Low levels are automatically determined from a measurement of the amplitude of the
signals acquired by the oscilloscope. Alternatively, they can be manually set by the user. 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.
Logical Decoding
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 specific to the protocol (Header/ID, Address Labels, Data
Length Codes, Data, CRC, Parity Bits, Start Bits, Stop Bits, Delimiters, Idle Segments, etc.).
Message Decoding
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 for the duration of the acquisition, from as little as one serial data message acquisition to
many thousands. In the case of long acquisitions, only the most important information is highlighted, whereas with
the shortest acquisition, all information is displayed with additional highlighting of the complete message frame.
User Interaction
Your interaction with the software in many ways mirrors the order of the algorithms. You will:
l
Assign a protocol/encoding scheme and input sources to one of the four decoder panels using the Serial Data
and Decode Setup dialogs.
l
Complete the remaining subdialogs required by the protocol/encoding scheme.
l
Work with the decoded waveform, result table, and measurements to analyze the decoding.
2
