EEPROM Dump

With the serial port yielding nothing, I turned to the other accessible memory in the system: the AT24C512 I2C EEPROM at U6, which stores the entire D2Audio DSP firmware.

Identifying the chip

The SOIC-8 package carries Atmel markings: ATMLH007 / 2FCD / CN / 20071YC. The 2FC marking code identifies this as an AT24C512 — a 512Kbit (64KB) I2C serial EEPROM. Date code places manufacture in early 2007, consistent with the amp’s design era. The chip operates at 2.5V to 5.5V with I2C clock speeds up to 1MHz.

The AT24C512’s pinout on this SOIC-8 package:

Pin	Function	Notes
1	A0	Address bit 0 (floats to GND internally)
2	A1	Address bit 1 (floats to GND internally)
3	A2	Address bit 2 (floats to GND internally)
4	GND	Ground
5	SDA	Serial data
6	SCL	Serial clock
7	WP	Write protect (floats to GND = writes enabled)
8	VCC	Power supply

With all address pins at GND, the chip responds at I2C address 0x50.

The read

I used a CH341A USB programmer in I2C mode with an SOIC-8 clip, connected directly to U6 with the amplifier powered off. The CH341 supplies 3.3V to the EEPROM through the clip, keeping the D2-81431 and LPC2103F unpowered to avoid bus contention.

ch341eeprom -v -s 24c512 -r u6_eeprom_dump.bin

The tool detected the CH341 at 1a86:5512 in EPP/I2C mode and read all 65,536 bytes at 100kHz. I performed a second read to verify — both dumps are byte-identical (SHA-256: 54091da5bb3b40a1e909bf781e9a2abce1c6335d0c92f01741efad3fb9707bf3).

What we found

The EEPROM is only 26% utilized:

Region	Address Range	Size	Contents
Data	0x0000 – 0x4298	17,049 bytes	D2-81431 DSP firmware
Empty	0x4299 – 0xFFFF	48,487 bytes	Erased (0xFF)

17,049 bytes divides evenly into 5,683 24-bit words, which is exactly the word size of the D2Audio DSP architecture (Motorola 56300 family). This is not a coincidence — the entire data region is a stream of 24-bit DSP words packed big-endian into the EEPROM’s byte-addressable space.

The data is NOT encrypted

Initial byte-level entropy analysis looked discouraging — all 256 byte values present, roughly uniform distribution. But analyzing at the correct granularity, 24-bit words, told a very different story.

The critical finding: 70.3% of all 24-bit words have their least significant bit set to 0. Truly encrypted or scrambled data would show 50% ± 1%. A 20-point bias is a dead giveaway that we are looking at real coefficient data, not ciphertext.

Why the byte-level analysis was misleading

Byte-level entropy can look uniform even when the underlying 24-bit words have strong structure. A 24-bit coefficient like 0x2C4800 has three bytes (0x2C, 0x48, 0x00) that individually contribute to a flat byte histogram, but the word as a whole has a clear LSB of 0. The D2Audio DSP uses 24-bit fixed-point arithmetic (Q23 format), where small coefficient values naturally cluster around zero with even LSBs.

A reference to “encryption” in the Renesas EEPROM app note (R32AN0006) turned out to refer to encryption within the Audio Canvas III design files on the PC, not in the EEPROM image itself. The boot ROM loads EEPROM data raw.

Boot header

The first two 24-bit words form a complement pair:

• Word 0: 0x000008 (+8 in 24-bit signed)
• Word 1: 0xFFFFF8 (-8 in 24-bit signed)
• Sum = 0 in 24-bit arithmetic — a classic integrity check

This is consistent with a boot header that the D2-81431’s boot ROM validates before loading the rest of the image.

Regional structure

The LSB bias is not uniform across the image — it varies by region, revealing the internal structure of the firmware:

Word Range	Bit-0 = 0	Interpretation
0–499	53.2%	Near random — program code or boot header
500–5500	67–80%	Strong bias — coefficient and parameter data
5500+	55.7%	Returns toward random — possible program tail

The Hamming distance between adjacent words follows a near-perfect binomial distribution centered at 12 bits, consistent with independent coefficient values rather than structured program code.

Identified DSP filters

Analyzing 24-bit word quintuplets as potential biquad filter coefficients revealed recognizable audio processing stages. A second-order IIR biquad filter has the transfer function H(z) = (b0 + b1·z⁻¹ + b2·z⁻²) / (1 + a1·z⁻¹ + a2·z⁻²), requiring five coefficients per stage.

Subwoofer crossover (word 3299): b0 = −0.3476, b1 = −0.6833, b2 = −0.3120. The frequency response shows +47.5 dB at 20 Hz rolling off to −4.2 dB at 10 kHz — a textbook low-pass filter for subwoofer duty.

Subsonic high-pass stages: Multiple HPF groups found in words 0–500, consistent with subsonic rumble protection (removing content below approximately 20 Hz to protect the driver from inaudible excursion).

PWM correction filters: Approximately 20 filter groups with peaking behavior at 8–16 kHz, consistent with the D2-81431’s patented adaptive PWM frequency response correction — compensating for the output LC filter and speaker impedance characteristics.

Parametric EQ: Several groups matching peaking/parametric EQ patterns, likely the speaker EQ presets (FLAT and model-specific profiles that the front panel menu exposes).

Auto-correlation analysis reveals weak periodicity spikes at intervals of 6 and 12 words, consistent with the DSP’s biquad cascade structure: five coefficients per biquad plus one control/routing word equals six words per filter stage.

Two layers of DSP configuration

The firmware analysis of the LPC2103F decoded the complete I2C protocol for the D2-81431, which reveals how this EEPROM image fits into the system. There are two independent layers of DSP configuration, and this EEPROM is the foundation layer.

Layer 1 — EEPROM boot image (this dump): The D2-81431 loads all 5,683 24-bit words from U6 at power-on via its own I2C master on GPIO6/7. This establishes the baseline DSP topology: the filter chain structure, biquad routing, protection limiters, PWM correction stages, and initial coefficient values. The subsonic HPFs, the PWM correction filters, and the base crossover filter identified above are all part of this boot image. They define the canvas — the audio processing architecture the D2-81431 runs.

Layer 2 — MCU runtime commands (LPC2103F firmware): After the D2-81431 boots from this EEPROM, the LPC2103F sends I2C commands at slave address 0xB2 to modify specific coefficient registers in the running DSP. The six speaker EQ presets (FLAT, DUAL8, BSUB8, BSUB10, BSUB12, HSUB10) each overwrite between 11 and 17 biquad coefficient sets. The sound modes (BYPASS, MUSIC, MOVIE) modify 2 coefficient slots each. Crossover, phase, and volume each write to their own register addresses. These runtime commands do not replace the EEPROM image — they modify the live coefficient RAM on top of whatever the boot image loaded.

The parametric EQ groups identified in the EEPROM are the baseline coefficient slots that the MCU’s speaker EQ presets reprogram at runtime. When the user selects BSUB10, the MCU sends 17 seven-byte I2C packets, each writing a 24-bit fixed-point coefficient to a specific register address in the D2-81431’s coefficient RAM — overwriting 17 of the biquad stages that the EEPROM originally loaded with enclosure-specific corrections for a bass reflex 10-inch subwoofer. When the user selects FLAT, the MCU sends 11 packets that presumably restore those same register addresses to unity-gain or bypass values.

Two different EEPROMs

The AT24C512 at U6 is the D2-81431’s firmware EEPROM — it stores the DSP boot image (this dump). User settings (volume, crossover, phase, EQ preset selection, etc.) are stored separately in the D2-81431’s small on-chip EEPROM, accessed by the LPC2103F via I2C register 0 as a 16-byte read/write. These are two different storage locations on two different chips. U6 holds the DSP program; the D2-81431’s internal EEPROM holds the 16-byte settings array that tells the MCU which presets to load at boot.

The MCU’s I2C command packets are stored in the LPC2103F’s .data section (flash offset 0x7A88, copied to SRAM at boot). The SRAM-to-flash mapping is flash_offset = (sram_addr - 0x40000000) + 0x7A88. Every coefficient the MCU sends at runtime can be traced to a specific address in the LPC2103F’s flash dump, and every register it writes to corresponds to a biquad filter slot in the D2-81431 that was originally populated by this EEPROM boot image. The Audio DSP Pipeline page documents the complete I2C protocol.

What the dump is good for

The EEPROM dump is a byte-perfect backup of the DSP firmware. If the EEPROM ever fails or gets corrupted — a real risk with a chip from 2007 that has been through thousands of thermal cycles — this dump can restore the amplifier’s audio processing to its exact factory state. Writing it back requires either a CH341 clip (offline) or the LPC2103F’s I2C relay procedure via the UPDATE switch (online, but requires the dealer tool).