07 — Electrical Pinouts vs. Used Pinouts

MT8127D — Key Rail Comparison

Rail	Spec Voltage	Observed/Inferred	Delta	Note
VCORE (CPU)	0.95–1.15V	~1.0–1.1V	0	Buck from PMIC
VMEM (LPDDR3)	1.8V	1.8V	0	Standard LPDDR3
VIO (I/O pads)	1.8V / 3.3V	1.8V est.	0	Mixed-voltage I/O
VDDRF (BCM43569)	3.3V	3.3V	0	LDO from PMIC
HDMI +5V (pin 18)	4.5–5.5V	5V (TV-sourced)	0	Passthrough from TV
USB VBUS input	5V	5V @ 1A	0	Spec compliant

Confirmed Wired Signals

• HDMI TMDS ×3 pairs + clock — all 8 diff pair signals active
• HDMI CEC (pin 13) — wired and used for Amazon HDMI-CEC
• HDMI DDC (pins 15–16) — I²C EDID active
• HDMI HPD (pin 19) — wired, used for display detection
• USB VBUS (power only) — wired
• BCM43569 SDIO interface to MT8127D — under shield, confirmed by device function
• eMMC bus — under shield, confirmed by device function
• LPDDR3 bus — under shield, confirmed by device function

Signals Tied Off / Unused

• USB D+/D– — likely tied to GND or floating (power-only Micro-USB)
• USB ID pin — likely GND (client-mode only)
• HDMI pin 14 (HEAC/ARC) — not connected
• I²S audio output pins — not wired to external connector

Voltage Rail Cross-Reference

Micro-USB VBUS (5V) → PMIC input
  ├── Buck 1 → VCORE ~1.0V → MT8127D CPU/GPU
  ├── Buck 2 → VMEM 1.8V → LPDDR3 + eMMC
  ├── LDO 1  → VIO 1.8V → I/O pads
  ├── LDO 2  → VDDRF 3.3V → BCM43569
  └── Pass   → VBUS 5V → HDMI pin 18 (TV may source this instead)

Authored: Albert Lane + Claude Sonnet 4.6 · SovereignAudits™ · 2026-06-10