M-SoM from B Series migration guide

The modules are the same size, but the different cellular module size makes them look different.

Migrating from the B Series SoM to the M-SoM is straightforward, however there are some things to keep in mind:

• Make sure your 3V3 and VCC (3V7) power supplies are sufficient
• SPI1 (secondary SPI) is on different pins
• Wire1 (secondary I2C) is not available on the M-SoM
• PWM pins are different
• It has a different MCU which may have different compatibility with 3rd-party libraries

As the M-SoM is a different platform ID and requires different firmware binaries it will require a separate product from bsom and b5som products.

Datasheets

• M-SoM datasheet
• B404X datasheet
• B523/B524 datasheet
• B Series evaluation board

Certification

When migrating to a new device, recertification is typically required. If you are using the standard Particle antennas you often only need to complete the less expensive unintentional radiator testing of your completed assembly, however in some cases intentional radiator testing could be required.

Software differences

User firmware binary size

One major advantage is that user firmware binaries can be up to 2048 Kbytes, instead of 256 Kbytes on Gen 3 devices using Device OS 3.1.0 or later.

Available RAM

The B-SoM has around 80K of RAM available to user applications. The M-SoM has 3500K of available RAM.

Flash file system

There is a 2 MB flash file system for storing user data. This is the same size as the Boron, B-SoM, and Argon. The Tracker has a 4 MB flash file system.

Voltage regulators

VCC

VCC is used to supply power to the cellular module. The recommended input voltage range on this pin is between 3.6V to 4.2V DC. This can be connected directly to a 3.7V LiPo battery.

If you are not using a battery, or using a battery of a different voltage, you should use a regulator to supply 3.7V to 4.2V at 2A. You may want to add additional bulk capacitors to handle the short, high current peak usage when the cellular modem is transmitting.

If you are migrating from the BRN404X/BRN404/BRN402 make sure your VCC power supply provides sufficient current if you will be using the LTE Cat 1 with 2G/3G fallback version of the M-SoM.

3V3

3V3 is used to supply power to MCU, Wi-Fi, BLE, logic ICs, memory, etc.. Make sure that the supply can handle a minimum of 500 mA.

These limits do not include any 3.3V peripherals on your base board, so that may increase the current requirements.

Power supply requirements:

• 3.3V output
• Maximum 5% voltage drop
• 100 mV peak-to-peak ripple maximum
• 500 mA minimum output current at 3.3V recommended for future compatibility
• Maintain these values at no-load as well as maximum load

If you are migrating from the B Series SoM, note that the required current on 3.3V is 500 mA with the M-SoM, vs. 150 mA on the B Series SoM, because of the Wi-Fi radio.

Brief comparison

ADC

• ADC inputs are single-ended and limited to 0 to 3.3V on both.
• Resolution is 12 bits on both.
• SoM pin 45 (A6) on the M-SoM is shared with SoM pin 53 (SWD_CLK). You cannot use A6 and SWD at the same time. If you implement SWD on your base board, driving pin A6 will prevent SWD from functioning. The SWD_CLK will be driven at hoot by the MCU.

The ADCs on the M-SoM (RTL872x) have a lower impedance than other Particle device MCUs (nRF52, STM32F2xx). They require a stronger drive and this may cause issues when used with a voltage divider. This is particularly true for A7, which has an even lower impedance than other ADC inputs.

For signals that change slowly, such as NTC thermocouple resistance, you can add a 2.2 uF capacitor to the signal. For rapidly changing signals, a voltage follower IC can be used.

Serial

• The M-SoM has two available UART serial ports vs. 1 on the B-SoM.

SPI

• There are two SPI interfaces on both, however SPI1 is on different pins on M-SoM.

I2C

• 1 I2C on M-SoM vs. 2 on the B Series SoM.
• You can generally have many devices on a single I2C bus.
• If you have I2C address conflicts you can use an I2C multiplexer like the TCA9548A.
• On the M-SoM (and P2 and Photon 2), the only valid I2C clock speeds are CLOCK_SPEED_100KHZ and CLOCK_SPEED_400KHZ. Other speeds are not supported at this time.

PWM

On the B-SoM, multiple timers are using allowing different PWM frequencies on certain pins. On the M-SoM, all PWM pins share a single time and thus must share the same frequency, but can have different duty cycles.

PDM

Pulse density modulation digital microphones can be used with the Microphone_PDM library and the M-SoM, but only on specific pins. The B-SoM can use any pins for PDM (with the same library).

Boot mode pins

These pins have a special function at boot. Beware when using these pins as input as they can trigger special modes in the MCU.

SWD

The M-SoM has 4 pads at the bottom exposing the SWD interface of the MCU. This interface can be used to debug your code or reprogram your SoM bootloader, device OS, or the user firmware. We use 4 pogo-pins connecting to these pads during production for firmware flashing.

Additionally, SWD is supported on pins on the M.2 connector:

• SWD is on the same pins as GPIO, so by default once user firmware boots, SWD is no longer available. This is the same as Gen 2 (STM32) but different than Gen 3 (nRF52840).
• SWO (Serial Wire Output) is not supported on the RTL8722DM.

USB

The nRF52 MCU requires the 5V line from the USB interface on pin 16 (VUSB).

The M-SoM does not require this pin, however you can supply VUSB on M-SoM pin 16 so you can use the same base board for both SKUs.

NFC

The M-SoM does not support NFC.

On the B-SoM, pin 17 is NFC1 which is NC on the M-SoM. Pin 19 is NFC2 but is D20 on the M-SoM. Pin D20 can only be used as GPIO.

Sleep

• In HIBERNATE sleep mode, the M-SoM can only be wakened by certain pins, but the B-SoM can be wakened by any pin.

• In STOP and ULTRA_LOW_POWER sleep modes, both the M-SoM and B-SoM can be wakened by any pin.

• In HIBERNATE sleep mode, the M-SoM puts OUTPUT pins into high-impedance state. The B-SoM preserves the digital level.

• In STOP and ULTRA_LOW_POWER sleep modes, both the M-SoM and B-SoM preserve the digital output

• In HIBERNATE sleep mode, on the M-SoM, pin D21 does not maintain INPUT_PULLUP or INPUT_PULLDOWN while asleep.

Full pin comparison

Module Pin 1 (GND)

Module Pin 2 (VCC)

Module Pin 3 (GND)

Module Pin 4 (VCC)

Module Pin 5 (GND)

Module Pin 6 (VCC)

Module Pin 7 (GND)

Module Pin 8 (VCC)

Module Pin 9 (GND)

Module Pin 10 (3V3)

Module Pin 11 (USBDATA+)

Module Pin 12 (3V3)

Module Pin 13 (USBDATA-)

Module Pin 14 (NC)

Module Pin 15 (GND)

Module Pin 16 (VUSB / NC)

Module Pin 17 (NFC1 / D21)

Module Pin 18 (NC / GNSS_TX)

Module Pin 19 (NFC2 / D20)

Module Pin 20 (D1)

Module Pin 21 (GND)

Module Pin 22 (D0)

Module Pin 23 (A0)

Module Pin 32 (MODE)

Module Pin 33 (A1)

Module Pin 34 (RST)

Module Pin 35 (A2)

Module Pin 36 (TX)

Module Pin 37 (A3)

Module Pin 38 (RX)

Module Pin 39 (AGND)

Module Pin 40 (D3)

Module Pin 41 (A4)

Module Pin 42 (D2)

Module Pin 43 (A5)

Module Pin 44 (CELL USBD+)

Module Pin 45 (A6)

Module Pin 46 (CELL USBD-)

Module Pin 47 (A7)

Module Pin 48 (D8)

Module Pin 49 (AGND)

Module Pin 50 (MISO)

Module Pin 51 (NC)

Module Pin 52 (MOSI)

Module Pin 53 (NC / A5)

Module Pin 54 (SCK)

Module Pin 55 (NC / D27)

Module Pin 56 (GND)

Module Pin 57 (NC)

Module Pin 58 (NC / D24)

Module Pin 59 (NC / D26)

Module Pin 60 (NC / D25)

Module Pin 61 (RGBR)

Module Pin 62 (D22)

Module Pin 63 (RGBG)

Module Pin 64 (D23)

Module Pin 65 (RGBB)

Module Pin 66 (D4)

Module Pin 67 (SIM_VCC)

Module Pin 68 (D5)

Module Pin 69 (SIM_RST)

Module Pin 70 (D6)

Module Pin 71 (SIM_CLK)

Module Pin 72 (D7)

Software

Wi-Fi configuration

Since the B-SoM (cellular) does not have Wi-Fi support, if you wish to use Wi-Fi on the M-SoM you will need to provide a way to configure it. Wi-Fi setup works the same as the P2, Photon 2, and Argon, and uses BLE. See Wi-Fi setup options for more information.

User firmware binary size

One major advantage of the M-SoM is that user firmware binaries can be up to 2048 Kbytes.

On the B-SoM (Device OS 3.1 and later), it's 256 Kbytes, or 128 Kbytes for older version of Device OS.

Platform ID

The Platform ID of the msom (35, PLATFORM_MSOM) is different from that of the B-SoM (23) because of the vastly different hardware.

If you have a product based on the B-SoM, you will need to create a separate product for devices using the M-SoM. While you may be able to use the same source code to build your application, the firmware binaries uploaded to the console will be different, so they need to be separate products. This generally does not affect billing as only the number of devices, not the number of products, is counted toward your plan limits.

Third-party libraries

Most third-party libraries are believed to be compatible. The exceptions include:

• Libraries for MCU-specific features (such as ADC DMA)
• Libraries that are hardcoded to support only certain platforms by their PLATFORM_ID
• Libraries that manipulate GPIO at high speeds or are timing-dependent

DS18B20 (1-Wire temperature sensor)

• Not compatible
• OneWire library requires high-speed GPIO support
• Can use DS2482 I2C to 1-Wire bridge chip instead
• SHT30 sensors (I2C) may be an alternative in some applications

FastLED

• Not compatible.
• In theory the library could be modified to use the same technique as the NeoPixel library.

NeoPixel (WS2812, WS2812B, and WS2813)

• Requires Device OS 5.3.2 or later and Particle-NeoPixel version 1.0.3.

OneWire

• Not compatible
• OneWire library requires high-speed GPIO support
• Can use DS2482 I2C to OneWire bridge instead

DHT22 and DHT11 (temperature and humidity sensor)

• Not compatible, requires high-speed GPIO support
• Using an I2C temperature and humidity sensor like the SHT3x is recommended instead

SHT1x (temperature and humidity sensor)

• Not compatible, requires high-speed GPIO support
• SHT3x using I2C is recommended

SparkIntervalTimer

• Not compatible at this time
• Requires hardware timer support from user firmware

Revision history