Table of Contents
Instrument cluster — board teardown & chip map
A look inside the U5 instrument cluster (the IP module, board marked MAS861 EXCITE, hardware 861921104, built 2022-05). It is a small embedded-Linux computer: an NXP i.MX6 application processor driving the dashboard panels, with a companion safety MCU for the warning lamps. Photos and chip identification below.
The main chips
| Ref | Part | What it is / does |
|---|---|---|
| U100 | NXP i.MX6 Dual (``MCIMX6D6AVT08AD``) | The main processor — two Arm Cortex-A9 cores at 800 MHz, automotive grade. Runs the Linux UI and draws all the gauges, drive-mode artwork and start-up animation. |
| U500 | NXP MMPF0100 (PMIC) | Power-management IC. Generates every voltage rail the i.MX6 needs from the board's supply. |
| U300 (+ U301) | ISSI ``IS46TR16128C`` DDR3 SDRAM | The processor's working memory (DDR3). Two devices for a 32-bit bus. |
| U401 | TI ``DS90UB940A`` FPD-Link III deserializer | The single coax (FAKRA) link to the head unit. The head unit sends the cluster the reverse/backup-camera video over it (shown on the cluster when you select reverse — handled by ``libmas861video.so`` on ``/dev/video0``), and the same link is the bidirectional data + firmware-update back-channel to the head unit. |
| U900, U902 | TI/National ``DS90CF386`` LVDS receivers (two of them) | Convert the LVDS display signal into the parallel RGB that drives the two LCD panels (left “trip data” and the centre speedometer). |
| U804 (pair) | NXP ``TJA1044`` CAN transceivers | The physical interface to the vehicle CAN bus. Everything the cluster shows (speed, gear, lamps) arrives as CAN messages through these. Paired with EPCOS B82793 common-mode chokes. |
| companion MCU | NXP S12 / HCS12 | Separate safety microcontroller that drives the legally-mandated warning lamps. Deliberately independent of Linux, so the tell-tales keep working even if the UI hangs. |
| UGSP3708 | buzzer | The chime/gong speaker for the warning sounds. |
Also on the board: a 20-pin debug header, a USB port, the FAKRA coax for the FPD-Link video, the blue 32-way vehicle connector (power, ignition, Infotainment CAN), and the display ribbon (FFC) connectors.
Photos — front side
U100 — NXP i.MX6 Dual (the processor)
U500 — NXP MMPF0100 (power management)
U300 — ISSI DDR3 memory
U401 — TI DS90UB940A (FPD-Link III: reverse-camera + head-unit back-channel)
U900 / U902 — TI DS90CF386 (LVDS display receivers)
U804 — NXP TJA1044 (CAN transceiver)
The other side of the board
The reverse of the PCB carries the companion microcontroller and the cluster's audio and power-supervision support. The board-ID sticker reads 型号 (model) 861921104E and 名 (name) S22060123-1 — a hardware-revision E (the EU track), matching the ``861921104E`` part number the cluster reports over UDS.
| Ref | Part | What it is / does |
|---|---|---|
| U800 | NXP / Freescale ``S912XHY256VLM`` (MC9S12XHY256) | The companion 16-bit “safety” microcontroller — an S12X automotive part made specifically for instrument clusters: on-chip CAN + LIN, stepper-motor control with stall detection, and LCD drive; 256 KB flash, 12 KB RAM, 8 KB EEPROM, 100-pin LQFP. It is the node actually on the vehicle CAN bus, and it guarantees the mandatory warning lamps independently of the Linux side. This is the chip that runs the ``mas861.s19`` MCU firmware. |
| U301 | ISSI ``IS46TR16128C`` DDR3 SDRAM | The second DDR3 device of the i.MX6's memory pair (its twin U300 is on the front) — mounted on the back under the processor to complete the 32-bit bus. |
| U700 | ROHM ``BD4275FP2`` | Automotive 5 V / 0.5 A LDO regulator with a built-in reset / voltage-detector (TO-263-5F). Supplies and supervises the microcontroller rail — it holds the MCU in reset until the rail is good (reset threshold ~4.6 V). |
| U803 | Nuvoton ``ISD2360SYI`` ChipCorder | A voice record / playback IC (SPI, up to 64 s of audio, 16-SOIC). This is the cluster's chime / warning-sound store-and-play engine — the source for the buzzer. |
| U903 | MPS ``MPSM24`` / ``M3387L`` (24-pin QFN) | A Monolithic Power Systems device next to the audio section — most likely the amplifier that drives the chime speaker from the ISD2360 (identification tentative). |
| U801 | Microchip / Atmel ``AT24`` I²C EEPROM (``ATMLH119 04CM``) | A small serial EEPROM for configuration / calibration data. |
Also on this side: the input-protection diodes D701 / D703, a switching-supply module (TUS700, top-left) and the bulk of the board's decoupling.
U800 — NXP/Freescale S912XHY256 (the companion safety MCU)
U700 — ROHM BD4275FP2 (5 V LDO + reset supervisor)
U803 — Nuvoton ISD2360 (chime / warning-sound playback)
U903 — MPS audio amplifier (chime speaker)
U301 — ISSI DDR3 (second device)
U801 — Atmel AT24 I²C EEPROM
Power input (D703 / TUS700 region)
Chip markings read directly from the dies; U800 confirmed against NXP's ``S912XHY256`` product listing. Date / lot codes: U800 lot ``QNH2202C``, U803 date ``2142`` (2021 wk 42), U301 ``IS46TR16128C-125KBLA1``.
How it all connects
- Vehicle CAN → TJA1044 (U804) → the S12 microcontroller (U800, ``S912XHY256``): the MCU is the only node on the bus. It reads speed, gear, state-of-charge and the lamp requests, drives the mandatory warning lamps itself, and passes the rest to the i.MX6 over a private SPI link. The cluster cannot be driven by the head unit directly.
- i.MX6 (U100) → LVDS → DS90CF386 (U900/U902) → the two dashboard LCD panels (it draws all the gauges and artwork).
- Head unit → coax (FPD-Link III) → DS90UB940A (U401): the reverse-camera image, plus the data/firmware back-channel. (The right “media” strip itself is drawn locally by the i.MX6, not fed from here.)
- MMPF0100 (U500) powers the i.MX6; BD4275FP2 (U700) supplies and supervises the S12 MCU rail, which independently holds the safety tell-tales.
- Warning sounds: ISD2360 (U803) stores and plays the chimes → audio amp (U903) → the UGSP3708 buzzer on the front.
Photos and identification from a bench teardown of a spare unit. Chip markings read directly from the dies. The companion safety MCU — previously known only from the firmware — is now pinpointed as U800 on the reverse side (NXP/Freescale ``S912XHY256VLM``).