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BMI270 Molecule — Hardware Reference

~16×16 mm breakout for the Bosch BMI270 low-power 6-axis IMU (accelerometer + gyroscope). Brings out the full interface including the BMI270's auxiliary I²C master bus for slaving an external magnetometer.

Source: adom-inc/bosch-molecules/Moecule_BMI270_Bosch_V1 — imported 2026-04-17 (folder name misspelled Moecule upstream; we preserve that on disk)
KiCad project: Moecule_BMI270_Bosch_V1.kicad_pro
Wiki page: molecules/bmi270-bosch-v1-666000
Board: 17 contacts arranged as two rows at X=82 mm (west edge) and X=90 mm (east edge), single-sided, silk revision V1: 2025-09-04
IC: BMI270 (Bosch LGA-14, U1)

Component summary

Ref	Part	Function
U1	BMI270	6-axis IMU (accel + gyro), LGA-14
C1	100 nF 0402	VDDIO decoupling
C2	100 nF 0402	VDD decoupling
R1	10 kΩ 0402	Default pull-up on the `I2C / 0x69` strap net → +VDDIO
Logo1	Adom logo	silkscreen only

External contact map

Positions in mm on the front copper. Two columns: west edge (X=82, silk labels on the left side) and east edge (X=90, silk labels on the right side).

West edge (primary interface column)

Ref	Silk	Net	Role
MP2	`VDD`	`+VDD`	Main rail — 1.71–3.6 V
MC13	`VDD`	`+VDD`	(duplicate — a second VDD tap)
MC11	`VIO`	`+VDDIO`	Logic rail — 1.2–3.6 V (typically tied to VDD)
MC3	`CSB`	`CSB`	Interface select: tie high for I²C (default via R1), tie low for SPI
MC12	`I2C`	`/0x69/I2C`	I²C/SPI mode strap (see below)
MC1	`SDO`	`SDO/0x68/0x69`	I²C address strap (see below)
MC2	`0x69`	`/0x69/I2C`	Strap option: bridge to MC1 for 0x69
MC10	`0x68`	`GND`	Strap option: bridge to MC1 for 0x68
MP1	`GND`	`GND`	Ground

East edge (aux bus + interrupts + SPI lines)

Ref	Silk	Net	Role
MP3	`SDX`	`SDX`	BMI270 primary serial data (I²C = SDA, SPI = MOSI)
MC6	`INT1`	`INT1`	Interrupt / data-ready output 1
MC5	(no silk)	`ASCX`	Aux I²C SCL (BMI270 as I²C master to external mag)
MC4	`ASDX`	`ASDX`	Aux I²C SDA (BMI270 as I²C master to external mag)
MC7	`ASDX` (silk overlap)	`OSCB`	OSCB — SPI aux-bus clock for 4-wire internal slave-SPI debug
MC9	`OSCB` (silk overlap)	`OSDO`	OSDO — SPI aux-bus data out
MC8	`INT2`	`INT2`	Interrupt / data-ready output 2
MP4	`SCX`	`SCX`	BMI270 primary serial clock (I²C = SCL, SPI = SCK)

Reading the silk

The silk is cramped on the east edge and labels overlap. Use the netlist (above) as ground truth; the .kicad_pcb coordinates give the true ordering top-to-bottom (Y=60 → Y=76) on that side:

Y=60  MP3  SDX                 (primary MOSI / SDA)
Y=62  MC6  INT1
Y=64  MC5  ASCX  (aux I²C SCL)
Y=66  MC4  ASDX  (aux I²C SDA)
Y=70  MC7  OSCB
Y=72  MC9  OSDO
Y=74  MC8  INT2
Y=76  MP4  SCX                 (primary SCK / SCL)

Interface strap (CSB — I²C vs SPI)

CSB net state	Mode
Pulled high (default)	I²C
Pulled low (bridge MC3 to GND)	4-wire SPI

Schematic text annotation: "CSB shares SDO pullup when high." In practice: leave MC3 floating and the default R1 pull-up holds the chip in I²C mode.

I²C address strap

BMI270 I²C slave address is set by the SDO pin at power-up. On this molecule, SDO is brought out as a 3-way strap:

Strap	SDO tied to	I²C address
Bridge MC1 ↔ MC10 (silk `0x68`)	GND	0x68 (demo firmware target ✓, Bosch default)
Bridge MC1 ↔ MC2 (silk `0x69`)	`I2C/0x69` net (pulled up via R1)	0x69

Schematic text: "Jumper to GND (LOW): 0x68 (Default). Jumper to VDDIO (HIGH): 0x69."

CRITICAL for bring-up: the default with MC1 floating is undefined — SDO is weakly coupled through R1 (10 kΩ pull-up) to the I2C/0x69 net, which would resolve to 0x69 if the user hasn't bridged anything. The firmware expects 0x68, so MC1 must be solder-bridged to MC10 (the GND strap silk'd 0x68). Verify this physically on the board before flashing.

Aux I²C bus (for standalone BMM350 fusion)

The BMI270 can act as an I²C master to a single external sensor via its aux bus (ASCX / ASDX). On this molecule the aux pads are brought out to external contacts (MC4 / MC5) — they are NOT auto-wired to anything on the PCB. If you want the BMI270 to fuse with an external BMM350, you have to wire MC4/MC5 off-board to the BMM350 breakout's SDA/SCK pins.

For our demo firmware, the arm-side magnetometer fusion is handled by the BHI360/BHI385 combo molecules (which have the BMM350 on their own internal aux bus). The standalone BMI270 therefore runs in 6-DOF mode only; MC4/MC5 can be left unconnected.

Power

Rail	Voltage	Source
VDD	1.71–3.6 V	Host via MP2 (or MC13 as alternate tap)
VDDIO	1.2–3.6 V	Host via MC11

Datasheet annotation: "VDD/IO: 1.8 to 3.3. Typ: 685 µA." Typical active current is 685 µA with accelerometer + gyroscope in normal mode. For the demo: tie both VDD and VDDIO to +3.3 V.

Interrupts

INT1 (MC6) and INT2 (MC8) are push-pull active-low by default. Programmable for FIFO watermark, data-ready, any-motion, orientation, and the 8 kB feature engine (wrist-tilt, pickup, step counter). If unused → "If INT1,2 unused: DNC" (schematic note). Leave floating.

Wiring to the Arm RM2 I²C bus

BMI270 MP2 (VDD)  ──── RM2 +3V3
BMI270 MC11 (VIO) ──── RM2 +3V3           (tie VDDIO = VDD)
BMI270 MP1 (GND)  ──── RM2 GND
BMI270 MP3 (SDX)  ──── RM2 GPIO4 (I²C0 SDA, shared bus)
BMI270 MP4 (SCX)  ──── RM2 GPIO5 (I²C0 SCL, shared bus)
BMI270 MC6 (INT1) ──── (optional)
BMI270 MC8 (INT2) ──── (optional)
BMI270 MC4/MC5    ──── (unused — aux bus)
BMI270 MC7/MC9    ──── (unused — slave-SPI debug)

Bridge MC1 ↔ MC10 (solder blob or 0 Ω) to force SDO → GND → address 0x68.

Gotchas for firmware bring-up

SDO strap is not GND by default — on the bare v1 board, the default (unbridged) state is 0x69 via R1. Bridge MC1↔MC10 before powering up or the firmware will miss the 0x68 probe.
CSB must be high for I²C mode. The R1 pull-up handles this; just don't accidentally ground MC3.
BMI270 needs a config blob upload at boot (~8 KB) before accel/gyro work — already handled in firmware/sensors/bmi270.c, but it means a cold-boot read of raw registers before config upload returns garbage.
VDDIO must come up before or with VDD, otherwise the chip can latch up. Sequencing is fine if both rails are tied together on the carrier.
Silk is cramped on the east edge — when in doubt, trust the netlist above or probe with a multimeter.
Aux bus (ASCX/ASDX) is NOT connected on-board to any slave sensor on this molecule. If you expect magnetometer data, you need the BHI combo molecule instead (or wire an external BMM350 manually to MC4/MC5).

# BMI270 Molecule — Hardware Reference

~16×16 mm breakout for the Bosch BMI270 low-power 6-axis IMU (accelerometer + gyroscope). Brings out the full interface including the BMI270's **auxiliary I²C master bus** for slaving an external magnetometer.

- **Source:** [adom-inc/bosch-molecules/Moecule_BMI270_Bosch_V1](https://github.com/adom-inc/bosch-molecules/tree/main/Moecule_BMI270_Bosch_V1) — imported 2026-04-17 (folder name misspelled `Moecule` upstream; we preserve that on disk)
- **KiCad project:** `Moecule_BMI270_Bosch_V1.kicad_pro`
- **Wiki page:** [molecules/bmi270-bosch-v1-666000](https://wiki-ufypy5dpx93o.adom.cloud/wiki/molecules/bmi270-bosch-v1-666000)
- **Board:** 17 contacts arranged as two rows at X=82 mm (west edge) and X=90 mm (east edge), single-sided, silk revision `V1: 2025-09-04`
- **IC:** BMI270 (Bosch LGA-14, U1)

## Component summary

| Ref | Part | Function |
|---|---|---|
| U1 | BMI270 | 6-axis IMU (accel + gyro), LGA-14 |
| C1 | 100 nF 0402 | VDDIO decoupling |
| C2 | 100 nF 0402 | VDD decoupling |
| R1 | 10 kΩ 0402 | Default pull-up on the `I2C / 0x69` strap net → +VDDIO |
| Logo1 | Adom logo | silkscreen only |

## External contact map

Positions in mm on the front copper. **Two columns:** west edge (X=82, silk labels on the left side) and east edge (X=90, silk labels on the right side).

### West edge (primary interface column)

| Ref | Silk | Net | Role |
|---|---|---|---|
| MP2 | `VDD` | `+VDD` | Main rail — 1.71–3.6 V |
| MC13 | `VDD` | `+VDD` | (duplicate — a second VDD tap) |
| MC11 | `VIO` | `+VDDIO` | Logic rail — 1.2–3.6 V (typically tied to VDD) |
| MC3 | `CSB` | `CSB` | **Interface select:** tie high for I²C (default via R1), tie low for SPI |
| MC12 | `I2C` | `/0x69/I2C` | I²C/SPI mode strap (see below) |
| MC1 | `SDO` | `SDO/0x68/0x69` | I²C address strap (see below) |
| MC2 | `0x69` | `/0x69/I2C` | Strap option: bridge to MC1 for 0x69 |
| MC10 | `0x68` | `GND` | Strap option: bridge to MC1 for 0x68 |
| MP1 | `GND` | `GND` | Ground |

### East edge (aux bus + interrupts + SPI lines)

| Ref | Silk | Net | Role |
|---|---|---|---|
| MP3 | `SDX` | `SDX` | BMI270 primary serial data (I²C = SDA, SPI = MOSI) |
| MC6 | `INT1` | `INT1` | Interrupt / data-ready output 1 |
| MC5 | *(no silk)* | `ASCX` | **Aux I²C SCL** (BMI270 as I²C master to external mag) |
| MC4 | `ASDX` | `ASDX` | **Aux I²C SDA** (BMI270 as I²C master to external mag) |
| MC7 | `ASDX` *(silk overlap)* | `OSCB` | OSCB — SPI aux-bus clock for 4-wire internal slave-SPI debug |
| MC9 | `OSCB` *(silk overlap)* | `OSDO` | OSDO — SPI aux-bus data out |
| MC8 | `INT2` | `INT2` | Interrupt / data-ready output 2 |
| MP4 | `SCX` | `SCX` | BMI270 primary serial clock (I²C = SCL, SPI = SCK) |

### Reading the silk

The silk is cramped on the east edge and labels overlap. Use the netlist (above) as ground truth; the `.kicad_pcb` coordinates give the true ordering top-to-bottom (Y=60 → Y=76) on that side:

```
Y=60  MP3  SDX                 (primary MOSI / SDA)
Y=62  MC6  INT1
Y=64  MC5  ASCX  (aux I²C SCL)
Y=66  MC4  ASDX  (aux I²C SDA)
Y=70  MC7  OSCB
Y=72  MC9  OSDO
Y=74  MC8  INT2
Y=76  MP4  SCX                 (primary SCK / SCL)
```

## Interface strap (CSB — I²C vs SPI)

| CSB net state | Mode |
|---|---|
| Pulled high (default) | I²C |
| Pulled low (bridge MC3 to GND) | 4-wire SPI |

Schematic text annotation: *"CSB shares SDO pullup when high."* In practice: leave MC3 floating and the default R1 pull-up holds the chip in I²C mode.

## I²C address strap

BMI270 I²C slave address is set by the SDO pin at power-up. On this molecule, SDO is brought out as a 3-way strap:

| Strap | SDO tied to | I²C address |
|---|---|---|
| **Bridge MC1 ↔ MC10 (silk `0x68`)** | GND | **0x68** (demo firmware target ✓, Bosch default) |
| Bridge MC1 ↔ MC2 (silk `0x69`) | `I2C/0x69` net (pulled up via R1) | 0x69 |

Schematic text: *"Jumper to GND (LOW): 0x68 (Default). Jumper to VDDIO (HIGH): 0x69."*

**CRITICAL for bring-up:** the default with MC1 floating is **undefined** — SDO is weakly coupled through R1 (10 kΩ pull-up) to the `I2C/0x69` net, which would resolve to 0x69 if the user hasn't bridged anything. The firmware expects **0x68**, so MC1 **must** be solder-bridged to MC10 (the GND strap silk'd `0x68`). Verify this physically on the board before flashing.

## Aux I²C bus (for standalone BMM350 fusion)

The BMI270 can act as an I²C master to a single external sensor via its aux bus (ASCX / ASDX). **On this molecule the aux pads are brought out to external contacts (MC4 / MC5)** — they are NOT auto-wired to anything on the PCB. If you want the BMI270 to fuse with an external BMM350, you have to wire MC4/MC5 off-board to the BMM350 breakout's SDA/SCK pins.

For our demo firmware, the arm-side magnetometer fusion is handled by the BHI360/BHI385 combo molecules (which have the BMM350 on their own internal aux bus). The standalone BMI270 therefore runs in 6-DOF mode only; MC4/MC5 can be left unconnected.

## Power

| Rail | Voltage | Source |
|---|---|---|
| VDD | 1.71–3.6 V | Host via MP2 (or MC13 as alternate tap) |
| VDDIO | 1.2–3.6 V | Host via MC11 |

Datasheet annotation: *"VDD/IO: 1.8 to 3.3. Typ: 685 µA."* Typical active current is 685 µA with accelerometer + gyroscope in normal mode. For the demo: tie both VDD and VDDIO to +3.3 V.

## Interrupts

INT1 (MC6) and INT2 (MC8) are push-pull active-low by default. Programmable for FIFO watermark, data-ready, any-motion, orientation, and the 8 kB feature engine (wrist-tilt, pickup, step counter). If unused → *"If INT1,2 unused: DNC"* (schematic note). Leave floating.

## Wiring to the Arm RM2 I²C bus

```
BMI270 MP2 (VDD)  ──── RM2 +3V3
BMI270 MC11 (VIO) ──── RM2 +3V3           (tie VDDIO = VDD)
BMI270 MP1 (GND)  ──── RM2 GND
BMI270 MP3 (SDX)  ──── RM2 GPIO4 (I²C0 SDA, shared bus)
BMI270 MP4 (SCX)  ──── RM2 GPIO5 (I²C0 SCL, shared bus)
BMI270 MC6 (INT1) ──── (optional)
BMI270 MC8 (INT2) ──── (optional)
BMI270 MC4/MC5    ──── (unused — aux bus)
BMI270 MC7/MC9    ──── (unused — slave-SPI debug)
```

**Bridge MC1 ↔ MC10** (solder blob or 0 Ω) to force SDO → GND → address 0x68.

## Gotchas for firmware bring-up

- **SDO strap is not GND by default** — on the bare v1 board, the default (unbridged) state is 0x69 via R1. Bridge MC1↔MC10 before powering up or the firmware will miss the 0x68 probe.
- **CSB must be high** for I²C mode. The R1 pull-up handles this; just don't accidentally ground MC3.
- **BMI270 needs a config blob upload at boot** (~8 KB) before accel/gyro work — already handled in `firmware/sensors/bmi270.c`, but it means a cold-boot read of raw registers before config upload returns garbage.
- **VDDIO must come up before or with VDD**, otherwise the chip can latch up. Sequencing is fine if both rails are tied together on the carrier.
- **Silk is cramped** on the east edge — when in doubt, trust the netlist above or probe with a multimeter.
- **Aux bus (ASCX/ASDX) is NOT connected on-board** to any slave sensor on this molecule. If you expect magnetometer data, you need the BHI combo molecule instead (or wire an external BMM350 manually to MC4/MC5).

BMI270_Bosch_v1