Reverse Engineering the Protocol

Using a logic analyzer, I captured I2C communication between a working Sony system and the wireless module.

Two key addresses control the system:

  • 0x40 → Control & Status
    • 0x13 → Status polling
    • 0x50 → 17-byte data blocks
    • 0x74 → Link trigger
  • 0x41 → DSP Configuration
    • Structured 5-byte sequences
    • Likely digital filter coefficients

Sony continuously polls these registers, expecting realistic responses and correct timing.

The Breakthrough

After emulating the correct I2C behavior—especially interactions around register 0x74—the system:

  • Accepts the emulated module
  • Raises the LINK signal
  • Transitions into an active state

This confirmed that pairing is enforced entirely through protocol behavior.

Timing Matters

Correct data alone is not enough.

  • Slight timing mismatch → system rejects the module
  • Accurate timing → successful pairing

Key signals involved:

  • INT → Event notification (pulsed)
  • LINK → Indicates successful pairing
  • RESN → Reset signal from Sony

Audio Injection (I2S)

Once pairing succeeds, audio can be injected via I2S.

Expected signals:

  • MCK ≈ 12.288 MHz
  • LRCK = 48 kHz
  • BCK ≈ 3.072 MHz

Important observation:

Without valid pairing, the system does not output I2S data at all.

Results

  • LINK signal goes HIGH
  • Front LED turns solid green
  • Audio plays normally

The TA-SA100WR is fully functional again—without the original Sony transmitter.

What This Reveals

  • The system is controlled entirely through I2C protocol
  • DSP parameters are dynamically configured
  • Audio is gated until pairing succeeds
  • The hardware itself isn’t locked—the protocol is

Future Work

  • Decode DSP data at address 0x41
  • Replace sniffed data with a smarter emulator
  • Explore multi-device pairing

Final Thought

Most proprietary systems aren’t truly locked—they’re just undocumented.