This encoder provides a simple ASCII transport layer for serial data. It uses the C0 and C1 ASCII control characters for this. You can find a C++ implementation here and a Python implementation here.
The encoded stream starts with a STX marker and ends with an ETX marker. STX and ETX occurrences in the stream are escaped and internally encoded as well so the receiver side can simply check for STX and ETX markers as frame delimiters. When using a strictly char based reception of packets encoded with DLE, STX can be used to notify a reader that actual data will start to arrive while ETX can be used to notify the reader that the data has ended.
Example:
[0, STX, DLE] -> [STX, 0, 0, DLE, STX + 0x40, DLE, DLE, ETX]
The encoded stream starts with DLE STX and ends with DLE ETX. All DLE occurrences in the stream are escaped with DLE. If the receiver detects a DLE char, it needs to read the next char to determine whether a start (STX) or end (ETX) of a frame has been detected.
Example:
[0, STX, DLE] -> [DLE, STX, 0, DLE, STX, DLE, DLE, DLE, ETX]