The author conducted a reverse engineering project on the A2B digital audio bus in an Evolute i-Space (Dongfeng Landian E5) crossover. The goal was to extract a digital audio signal for an aftermarket amplifier without interfering with the factory system.
Measurements using a 50 MHz FNIRSI 2C53T oscilloscope identified two separate interfaces on the 20-pin connector. Pins 5 and 15 were identified as a CAN bus operating at 500 kbit/s, while pins 6 and 16 carried a high-speed A2B signal.
The A2B bus analysis revealed a superframe frequency of 48 kHz and a data rate of 49.152 Mbit/s, consistent with Analog Devices documentation. However, direct extraction of audio data is complicated by the bus's master-slave architecture and the need for specific initialization commands.
The author opted to use an FPGA-based approach to capture and decode the raw A2B stream. A Sipeed Tang Primer 20K board with 128 MB of DDR3 memory was selected for its ability to record continuous traffic, costing approximately 5555 ₽ on AliExpress.
The project aims to create a passive device that records raw A2B data for analysis, followed by real-time decoding into S/PDIF or Toslink formats. This method avoids modifying the factory amplifier or violating the vehicle warranty.
