M-SoM from P2 migration guide

Pictures are not the same scale

The P2 module is a Wi-Fi SMD module that is mounted directly to your custom base board, while the M-SoM is a M.2 SoM that fits in a M.2 socket on your base board and has both cellular and Wi-Fi capabilities. The Particle M-SoM is larger and will not fit in the same footprint as the P2.

However, since the P2 has a Realtek RTL8721DM processor and the M-SoM has a Realtek RTL8722DM which is substantially similar, only having more GPIO, the migration should be relatively straightforward.

Datasheets

• M-SoM datasheet
• P2 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.

Hardware

Antenna

The P2 has a choice between an internal trace antenna on the module or an external antenna for Wi-Fi and BLE (shared) connected by a U.FL connector.

The M-SoM requires an external antenna for cellular. It also requires a separate external antenna for Wi-Fi and BLE (shared). All antennas are connected by U.FL connectors.

Voltage regulators

As the M-SoM requires dual supply voltages, you may want to consider using the PM-BAT power module that includes the PMIC, fuel gauge, and 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.

The P2 does not require this voltage.

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

Land pattern

The land pattern for the M.2 connector on the M-SoM is:

The P2 land pattern is:

ADC

• 6 ADC on the M-SoM vs. 6 on the P2
• On the P2, 2 of the ADCs are on the same pins as I2C
• 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.
• On the P2, VBAT_MEAS is a 5V tolerant ADC for measuring battery voltage. This is not present on the M-SoM as typically you will use a fuel gauge chip instead of the less accurate voltage measurement to measure battery SoC.
• ADC input A7 has a low impedance which may be an issue when supplied from a voltage divider. The other ADC inputs are comparable to the P2/Photon 2.

Serial

• The P2 has a third UART serial port; this does not exist on M-SoM

SPI

• Two SPI interfaces on both
• SPI uses the RTL872x SPI0 peripheral (50 MHz maximum speed) on M-SoM
• SPI1 uses the RTL872x SPI1 peripheral (25 MHz maximum speed) on M-SoM
• Note: The P2/Photon 2 maximum speeds for SPI and SPI1 are reversed from the M-SoM

I2C

• 1 I2C on both
• 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

• PWM pins vary between the P2 and M-SoM

PDM

Pulse density modulation digital microphones can be used with the Microphone_PDM library and the M-SoM, but only on specific pins that are different from the P2!

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.

Sleep

• In HIBERNATE sleep mode, the M-SoM and P2 can only be wakened by certain pins

• The WKP pin is A7 the M-SoM (and B-SoM) but is pin D10 on the P2.

• In HIBERNATE sleep mode, certain pins on the M-SoM and P2 do not preserve INPUT_PULLUP or INPUT_PULLDOWN while asleep. See details below.

M-SoM pins related to HIBERNATE sleep mode:

These P2 pins can wake from HIBERNATE sleep mode:

These P2 pins have special restrictions on using internal pull-up or pull-down while in HIBERNATE sleep mode. These also cannot be used as wake from hibernate sleep pins.

Full comparison

3V3

3V3_IO

3V3_RF

A0

A1

A2

A5

A5

A6

A7

AGND

CELL USBD-

CELL USBD+

CELL VBUS

CELL_RI

D0

D1

D10

D15

D16

D17

D18

D19

D2

D22

D23

D24

D25

D26

D27

D3

D4

D5

D6

D7

D8

D9

GND

GNSS_TX

MISO

MODE

MOSI

NC

RGBB

RGBG

RGBR

RST

S5

S6

SCK

SIM_CLK

SIM_DATA

SIM_RST

SIM_VCC

TX

USBDATA-

USBDATA+

VBAT_MEAS

VCC

Software

Wi-Fi configuration

Wi-Fi setup works the same as the P2, Photon 2, and Argon, and uses BLE. See Wi-Fi setup options for more information.

Platform ID

The Platform ID of the msom (35, PLATFORM_MSOM) is different from that of the P2 (32) because of the different hardware.

If you have a product based on the P2, 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 between the P2 and M-SoM as they share a similar MCU. The exceptions include:

• Libraries that are hardcoded to support only certain platforms by their PLATFORM_ID

Revision history