Using M.2 Connectors for MicroMod Modules

Overview

SparkFun's MicroMod ecosystem uses the M.2 Key E edge connector (75 pins, 0.5 mm pitch) to create swappable processor modules. A processor board (e.g., RP2040, ESP32, STM32) plugs into any compatible carrier board via a single M.2 edge connector.

In tscircuit, you model the M.2 connector as a <chip> component. The same component definition works on both sides:

• Processor board — the processor module exposes signals through the M.2 edge pads.
• Carrier board — the carrier hosts the physical M.2 socket and routes those signals to headers, sensors, or other peripherals.

MicroMod Signal Map

The MicroMod specification assigns each M.2 pin a fixed function. Odd-numbered pins are GND; even-numbered pins carry signals:

Pin	Signal	Notes
2	3V3	Regulated 3.3 V from carrier
4	3V3_EN	3.3 V enable (active high)
6	RESET	System reset (active low)
8	BOOT	Bootloader entry
10	USB_DM	USB D−
12	USB_DP	USB D+
16	UART_TX1	Primary UART transmit
18	UART_RX1	Primary UART receive
24	I2C_SDA	Primary I²C data
26	I2C_SCL	Primary I²C clock
34	SPI_CS	SPI chip select
36	SPI_SCK	SPI clock
38	SPI_COPI	SPI controller out
40	SPI_CIPO	SPI controller in
50	A0	Analog input 0
52	A1	Analog input 1
56	PWM0	PWM output 0
58	PWM1	PWM output 1
60	D0	Digital I/O 0
62	D1	Digital I/O 1
64–74	G0–G5	General-purpose I/O

All odd pins (1, 3, 5 … 75) are GND.

Defining the MicroMod Edge Connector

Model the connector as a <chip> with the full 75-pin label map. Because every odd pin is GND, omit them from schPinArrangement to keep the schematic readable — only signal pins appear on the schematic side.

Connecting a Processor Module

On the processor board, map your MCU's GPIO/peripheral pins to the correct M.2 pin numbers using the connections prop. Use pin number references (sel.U1.pin6) rather than label names when referencing chip pins — label names are not part of the global sel type union.

import { sel } from "@tscircuit/core"

// RP2040 processor mapped to MicroMod signals
<MicroModEdge
  name="J1"
  connections={{
    pin2: "net.3V3",                  // 3.3 V rail
    pin6: sel.U1.pin42,               // RUN / nRESET
    pin8: "net.BOOT",                 // BOOTSEL
    pin10: "net.USB_DM_EXT",          // USB D−
    pin12: "net.USB_DP_EXT",          // USB D+
    pin16: sel.U1.pin2,               // GPIO0 → UART_TX1
    pin18: sel.U1.pin3,               // GPIO1 → UART_RX1
    pin24: sel.U1.pin6,               // GPIO4 → I2C_SDA
    pin26: sel.U1.pin7,               // GPIO5 → I2C_SCL
    pin34: sel.U1.pin21,              // GPIO17 → SPI_CS
    pin36: sel.U1.pin22,              // GPIO18 → SPI_SCK
    pin38: sel.U1.pin23,              // GPIO19 → SPI_COPI
    pin40: sel.U1.pin20,              // GPIO16 → SPI_CIPO
    pin50: sel.U1.pin28,              // GPIO26/ADC0 → A0
    pin52: sel.U1.pin29,              // GPIO27/ADC1 → A1
    pin56: sel.U1.pin25,              // GPIO21 → PWM0
    pin60: sel.U1.pin8,               // GPIO6 → D0
    pin64: sel.U1.pin10,              // GPIO8 → G0
  }}
/>

Carrier Board Pattern

On the carrier board, the same connector definition appears but connections go outward to headers, sensors, or other chips:

<MicroModEdge
  name="J1"
  connections={{
    pin2: "net.3V3",
    pin16: "net.TX_TO_HOST",   // route UART_TX1 to debug header
    pin24: sel.SENSOR.SDA,     // route I2C_SDA to an on-board sensor
    pin26: sel.SENSOR.SCL,
    pin50: sel.ADC.IN1,        // route A0 to ADC chip
  }}
/>

All GND pins connect to net.GND via netlabel:

{/* Connect all GND pins with net labels instead of individual connections */}
<netlabel net="GND" anchorSide="top" connection="J1.pin1" />
<netlabel net="GND" anchorSide="top" connection="J1.pin3" />
{/* ... repeat for all odd pins up to pin75 */}

Footprint Note

The MicroMod Key E footprint string edge_connector_75p_m2_key_e is a custom footprint. If the autorouter or renderer does not recognize it, import the footprint from KiCad using the KiCad library importer:

import footprint from "@tscircuit/kicad-footprint/SparkFun-MicroMod/MicroMod_Key_E_Connector.kicad_mod"

See the Importing from KiCad guide for details on using .kicad_mod files in tscircuit.

Full Example: RP2040 Processor Board

The SparkFun MicroMod RP2040 Processor is a complete example that uses this connector. The tscircuit implementation is available in the sparkfun-boards repository as a reference for both the processor module and the M.2 edge connector wiring pattern.