M-SoM from E-Series Migration Guide

Pictures are not the same scale

The M-SoM (system-on-a-module) is a 4th-generation cellular and Wi-Fi device. It plugs into an M.2 NGFF connector on your custom circuit board and is intended for mass production use.

Like the E-Series module, it requires your own custom base board. One difference is that the M-SoM does not contain the PMIC and fuel gauge chips that the E-Series does.

Additionally, different dimensions makes it possible to include a LTE Cat 1 with 2G/3G fallback cellular modem, such as the Quectel EG91-E on the B524.

All E-Series models (except for the E404X) have been deprecated. It is recommended that you migrate to the B-SoM or M-SoM, and it is required to get LTE Cat 1 with 2G/3G fallback support in Europe, Australia, and New Zealand. While the E404X has the same footprint as the other E-Series modules, it contains the same MCU as the B-SoM.

¹The PMIC (power management IC) and fuel gauge are used with battery-powered applications. They're omitted from the SoM as they are not needed for externally powered solutions (grid or automotive power, for example). Additionally, you may want to use different models if you are making a solar-powered device, or using a different battery technology or multiple battery pack.

²The built-in Particle SIM card is free for use up to certain limits, no credit card required.

Datasheets

• M-SoM datasheet
• B-Series evaluation board
• E-Series datasheet

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.

Prototyping

The M-SoM cannot be used without a base board. Typically you will create your own board, however there are two off-the-shelf options available:

B-Series Eval board

The B-Series evaluation board provides a variety of interfaces and access to all ports and pins on the M-SoM. You can use the expansion connector to connect the evaluation board to a breadboard for prototyping. You can also add sensors and accessories using the Grove expansion connectors.

Mikroe Gen 3 SoM shield

The Gen 3 SoM shield connects a B-Series SoM to mikroBUS Click boards:

There is a huge library of mikroBUS Click expansion boards, however the caveat is that most of them do not already have a Particle software library. If the board is for a common sensor or chip, however, existing Particle libraries for the chip will typically work, even if not designed work with the Click.

For more information, see the Mikroe community page.

Creating a board

First SoM board tutorial

The SoM first board tutorial shows how to get started with the M.2 SoM boards by making the simplest possible design. It's an introduction to working with surface mount components you will need in order to make your own SoM base board.

Basic SoM design

This design is a bit more complicated, and includes the PMIC and Fuel Gauge chips that are present on the E-Series:

• RGB LED
• bq24195 PMIC
• MAX17043 Fuel Gauge
• USB Connector
• LiPo Connector (JST-PH)
• M.2 SoM Connector

This is the basic set of features you'll probably want to include in a LiPo battery-powered design. The Evaluation Board is also a good reference to use. This design, however, is simple enough that it can be hand-assembled, though you still need a reflow oven and some of the parts (in particular the fuel gauge and PMIC) are tiny and there are a lot of them.

This board a two-layer circuit board so it can be manufactured inexpensively and edited using the free version of Eagle CAD.

As this board doesn't really do much, you'll unlikely use it as-is, but you can use it as a tutorial for how to hook up the PMIC and fuel gauge.

Power requirements

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. Make sure that the supply can handle currents of at least 2 A.

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.

3V3

3V3 is used to supply power to RTL8722 MCU, 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

Software differences

User firmware binary size

One major advantage is that user firmware binaries can be up to 2048 Kbytes, instead of 128 Kbytes on Gen 2 devices.

Flash file system

There is a 2 MB flash file system for storing user data on the M-SoM. This is not available on the E-Series (except for the E404X).

Combined and resumable OTA

Over-the-air (OTA) updates have two features that can improve the speed and reliability of OTA updates:

• Combined OTA can combine Device OS and user firmware updates into a single binary that requires only one download and one reboot to install.
• Resumable OTA allows an update to resume from the point it stopped, instead of starting over from the beginning if interrupted.

Asset OTA

Asset OTA makes it possible to include bundled assets in an OTA software update that can be delivered to other processors and components in your product.

Increased API field limits

The maximum size of a variable, function parameter, or publish is 1024 bytes on the M-SoM vs. 864 bytes on the E-Series.

• These comparisons are between the STM32F205-based E-Series models, other than the E404X. The API field limits for the E404X (nRF52840) are the same as as the M-SoM.

Hardware differences

MCU

• These comparisons are between the STM32F205-based E-Series models, other than the E404X. The specifications for the E404X (nRF52840) are different.

BLE (Bluetooth LE)

• Bluetooth LE (BLE 5.0) is supported on M-SoM but not the E-Series (except for the E404X, which does support BLE).

GPIO

The MCP23008 is an 8-port GPIO expander that connects to I2C and works well with Gen 3 devices. You can connect up to 8 of them to a single I2C interface. the MCP23017 has 16-ports, and you can also connect 8 of them, for a total of 128 GPIO ports.

The application note AN013 Tracker GPIO shows how you can add additional GPIO to your Tracker One using the external M8 connector, however the same technique can also be used with the M-SoM. It includes both 3.3V and 5V design options.

5V tolerance

The other difference in the GPIO between Gen 2 and the M-SoM is with 5V tolerance. While both devices are 3.3V devices and only will drive 3.3V, the I/O pins on Gen 2 devices (with the exception of A3 and A6) are 5V tolerant. This allows a Gen 2 device to connect to some 5V peripherals directly.

You must not connect 5V peripherals to a Gen 3 or Gen 4 device. This includes GPIO, ports (serial, I2C, SPI), and ADC.

Interfacing with 5V peripherals can be done with a level shifter, a MOSFET, or a 5V GPIO expander.

SPI

• The M-SoM and E-Series both have two SPI ports.
• In most cases, you can share a single SPI bus with many peripherals.
• On the E-Series, SPI1 and SPI2 share the same MCU SPI interface but have different pin locations. You can only use one or the other.

Serial (UART)

There are more UART ports on the E-Series than the M-SoM. If you need more hardware serial ports, the best option is to use the SC16IS740 or its relatives like the SC16IS750. These devices connect by I2C or SPI, and you can add multiple ports this way.

¹CTS/RTS flow control only on Serial1. It is optional.

Supported Baud Rates:

Analog input (ADC)

The M-SoM does not have an many ADC ports as the E-Series. You can add additional ADC ports using a SPI or I2C ADC.

I2C

• 1 I2C on M-SoM. While it appears that there are 2 on the E-Series, they're just alternative pin assignments and you can really only use one at a time.
• 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.
• The E-Series I2C is 5V tolerant. This is not the case on the M-SoM, be sure you don't have pull-ups to 5V!
• If you need to interface to a 5V I2C bus you will need an I2C level shifter such as the PCA9306.
• 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 (Pulse-width modulation)

These are differences in pins that support PWM between the E-Series and M-SoM.

PWM - M-SoM

All available PWM pins on the M-SoM share a single timer. This means that they must all share a single frequency, but can have different duty cycles.

It is also possible to add an external PWM driver such as the PCA9685 which adds 16 outputs via I2C. You can add 62 of these to a single I2C bus for 992 PWM outputs! The Adafruit_PWMServoDriver library supports this chip on all Particle devices.

PWM - Gen 2

On the Electron and E-Series, this function works on pins D0, D1, D2, D3, A4, A5, WKP, RX, TX, B0, B1, B2, B3, C4, and C5 with a caveat: PWM timer peripheral is duplicated on two pins (A5/D2) and (A4/D3) for 7 total independent PWM outputs. For example: PWM may be used on A5 while D2 is used as a GPIO, or D2 as a PWM while A5 is used as an analog input. However A5 and D2 cannot be used as independently controlled PWM outputs at the same time.

Internal pull-up or pull-down

Internal (MCU) pull-up and pull-down can be enabled using the pinMode() function and INPUT_PULLUP or INPUT_PULLDOWN.

On the M-SoM, different GPIO pins have different pull values. On the E-Series pull is always approximately 40K.

Retained memory

The M-SoM has limited support for retained memory, also referred to as Backup RAM or SRAM.

Retained memory is preserved on RTL872x devices in the following cases:

Calling System.backupRamSync() will manually save the contents of retained memory to a dedicated flash page on the RTL872x processor and will be restored after the device is reset. You should avoid saving the data extremely frequently as it is slower than RAM and will cause flash wear and is relatively slow to execute.

Prior to Device OS 5.3.1, retained memory is not supported on RTL872x devices. The flash file system can be used, or you can use an external chip such as an I2C or SPI FRAM.

Retained memory is 3068 bytes.

Flash file system

The E-Series did not have a flash file system.

The M-SoM has 2 MB flash file system using the same POSIX API as Gen 3 devices. A small amount of space is reserved for system use including configuration data. Most of the space is available for user application use.

EEPROM

The EEPROM emulation API is the same across the E-Series and M-SoM.

• The E-Series had 2047 bytes of emulated EEPROM.
• The M-SoM has 4096 bytes of emulated EEPROM. On the M-SoM, P2, Photon 2, and Gen 3 devices, the EEPROM is actually just a file on the flash file system.

Interrupts

Interrupts - Gen 2

Not supported on the Electron/E series (you can't use attachInterrupt on these pins):

• D0, A5 (shared with MODE button)
• D7 (shared with BATT_INT_PC13)
• C1 (shared with RXD_UC)
• C2 (shared with RI_UC)

No restrictions on the Electron/E-Series (all of these can be used at the same time):

• D5, D6

Shared on the Electron/E-Series (only one pin for each bullet item can be used at the same time):

• D1, A4, B1
• D2, A0, A3
• D3, DAC
• D4, A1
• A2, C0
• A7 (WKP), B2, B4
• B0, C5
• B3, B5
• C3, TX
• C4, RX

Interrupts - M-SoM

There are no restrictions on interrupt pins on the M-SoM.

DAC

• Gen 2 devices have two DAC (digital-to-analog converter), on pins A3 and A6.

• The M-SoM and Gen 3 devices do not have built-in DAC, however they can easily be added by I2C or SPI to your base board.

CAN bus

• The M-SoM and Gen 3 devices do not support CAN on the MCU.
• The Tracker SoM includes CAN via a MCP25625 CAN interface with integrated transceiver.
• Both the MCP2515 and MCP25625 work with the library used on the Tracker and can be used to add CAN to other Gen 3 devices.

Sleep

• In HIBERNATE sleep mode, both the M-SoM and E-Series can only be wakened via the WKP pin.

• In HIBERNATE sleep mode, both the M-SoM and E-Series put pin in OUTPUT mode into high-impedance state.

• In STOP and ULTRA_LOW_POWER sleep modes, the M-SoM preserves the digital output, but the E-Series puts the pins in OUTPUT mode into high-impedance state.

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

M-SoM pins related to HIBERNATE sleep mode:

E-Series pins related to HIBERNATE sleep mode:

RTC (Real-time clock)

The E-Series module has support for an external lithium coin cell battery or supercap to power the STM32 internal RTC via the VBAT pin.

The M-SoM MCU does not have a dedicated RTC module that can be externally powered. This is also the case with the P2, Photon 2, and Gen 3 devices. If you need an externally powered RTC, one option is the AM1805/AB1805 real-time clock and hardware watchdog module, which is used on the Tracker SoM.

USB

• Both the E-Series and M-SoM assume the USB connector will be mounted on your base board. It is recommended that you add one to your base board for programming and troubleshooting.
• Gen 2 devices can emulate a USB mouse or keyboard over the USB port. This feature is available on the M-SoM but not available on Gen 3 (including B-SoM).
• Gen 2 devices can support two separate USB serial emulation streams over the USB port. Gen 3 devices only support the normal Serial interface.

PMIC and Fuel gauge

The E-Series, E-Series, Boron, and Tracker SoM all include the PMIC (bq24195) and battery fuel gauge (MAX17043) on the module itself.

On the M-SoM, the PMIC and fuel gauge are optional. For example, if you are powering by an external power supply and not using a battery, you can omit the components entirely.

PMIC Notes

When using the B-Series SoM with a bq24195 PMIC, note the following:

By default, the bq24195 sets the input current limit, which affects powering by VIN and VUSB, to 100 mA. This affects the VSYS output of the PMIC, which powers both the cellular modem and 3V3 supply, and is not enough to power the B-Series SoM in normal operation.

If your device has the default firmware (Tinker), it will attempt to connect to the cloud, brown out due to insufficient current, then the device will reset. This may result in what appears to be the status LED blinking white, but is actually rolling reboot caused by brownout.

A factory new B-Series SoM does not enable the PMIC setup. To enable the use of the bq21415, you must enable the system power feature PMIC_DETECTION in your code. This defaults to off because the B-Series SoM can be used without a PMIC, or with a different PMIC, and also requires I2C on D0/D1, and some base boards may use those pins as GPIO.

Because the input current limit does not affect the battery input (Li+), for troubleshooting purposes it can be helpful to attach a battery to help rule out input current limit issues. It's also possible to supply 3.7V via a bench power supply to the battery input, instead of VIN.

The input current limit can result in a situation where you can't bring up a B-Series SoM because it browns out continuously, but also cannot flash code to it to stop if from browning out. There are two general solutions:

• Attach a battery or supply by Li+ when bringing up a board.
• Use SWD/JTAG and reset halt the MCU. This will prevent it from connecting to the cloud, so you can flash Device OS and firmware to it by SWD.

The input current limit is actually controlled by three factors:

• The power source max current setting in the PMIC. The default is 900 mA. It can be set to 100, 150, 500, 900, 1200, 1500, 2000, or 3000 mA.
• It is also limited by the hardware ILIM resistor. On Particle devices with a built-in PMIC, this is set to 1590 mA, but if you are implementing your own PMIC hardware, you can adjust this higher.
• When connected by USB, it will use DPDM, current negotiation via the USB DP (D+) and DM (D-) lines.

Note that some 2A tablet chargers and multi-port USB power supplies supply 2A but do not implement DPDM; these will be treated as if VIN was used, and you must set the power source current, otherwise the input current will be limited to 900 mA, which is not enough to power a 2G/3G cellular modem without an attached battery.

Antennas

The M-SoM has U.FL antenna connectors:

• Cellular
• Wi-Fi and BLE (shared)
• GNSS (optional)

Full module pin comparison

3V3

A0

A1

A2

A3

A4

A5

A5

AGND

B0

B1

B2

B3

B4

B5

C0

C1

C2

C3

C4

C5

CELL USBD-

CELL USBD+

CELL VBUS

CELL_RI

D0

D1

D2

D20

D21

D22

D23

D24

D25

D26

D27

D3

D4

D5

D6

D7

D8

DAC

GND

GNSS_TX

LIPO

MISO

MODE

MOSI

NC

PMID

RESET

RGBB

RGBG

RGBR

RX

SCK

SIM_CLK

SIM_DATA

SIM_RST

SIM_VCC

STAT

TX

USBDATA-

USBDATA+

VBAT

VBUS

VCC

VDDA

VIN

WKP

Country compatibility

To be provided at a later date.

Software

Wi-Fi configuration

Since the E-Series (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 E-Series (10) because of the vastly different hardware.

If you have a product based on the E-Series, 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

SKUs

To be provided at a later date

Revision history