Photon 2 from Photon migration guide

Preliminary pre-release version 2022-04-16

This is an preliminary pre-release migration guide and the contents are subject to change. The Photon 2 design has not been finalized so changes are likely.

The Photon 2 is a development module with a microcontroller and Wi-Fi networking. The form-factor is similar to the Argon (Adafruit Feather), but the Photon 2 supports 2.4 GHz and 5 GHz Wi-Fi, BLE, and has much larger RAM and flash that can support larger applications.

It is intended to replace both the Photon and Argon modules. It contains the same module as the P2, making it easier to migrate from a pin-based development module to a SMD mass-production module if desired.

Feature Photon 2 Photon Argon
User application size 2048 KB (2 MB) 128 KB 256 KB
Flash file system1 2 MB 2 MB
MCU RTL8721DM STM32F205RGY6 nRF52840
Realtek Semiconductor ST Microelectronics Nordic Semiconductor
CPU Cortex M33 @ 200 MHz Cortex M3 @ 120 MHz Cortex M3 @ 64 MHz
Cortex M23 @ 20 MHz
RAM2 512 KB 128 KB 256 KB
Flash3 16 MB 1 MB 1 MB
Hardware FPU
Secure Boot
Trust Zone
Wi-Fi 802.11 a/b/g/n 802.11 b/g/n 802.11 b/g/n
  2.4 GHz
  5 GHz
Bluetooth BLE 5.0 BLE 5.0
NFC Tag External antenna required
Antenna Shared for Wi-Fi and BLE Wi-Fi only Separate Wi-Fi and BLE antennas
Built-in PCB antenna (Wi-Fi & BLE) Built-in PCB antenna (Wi-Fi) Built-in chip antenna (BLE)
Required external antenna (Wi-Fi)
Optional external (Wi-Fi & BLE)4 Optional external (Wi-Fi)4 Optional external (BLE)4
Peripherals USB 2.0 USB 1.1 USB 1.1
Digital GPIO 20 24 20
Analog (ADC) 6 13 6
Analog (DAC) 2
UART 3 2 1
SPI 2 2 2
PWM 6 12 8
I2C 1 1 1
CAN 1
I2S 1 1
JTAG
SWD

1A small amount of the flash file system is used by Device OS, most is available for user data storage using the POSIX filesystem API. This is separate from the flash memory used for Device OS, user application, and OTA transfers.

2 Total RAM; amount available to user applications is smaller.

3 Total built-in flash; amount available to user applications is smaller. The Argon also has a 4 MB external flash, a portion of which is available to user applications as a flash file system.

4 Onboard or external antenna is selectable in software.

There are two Photon 2 migration guides, depending on what you are migrating from:

Hardware

Battery support

The Photon 2 has a connector for a Li-Po battery and built-in charger. The Photon does not include battery power functionality.

No 5V tolerance!

On Gen 2 devices (STM32F205), most pins are 5V tolerant. This is not the case for Gen 3 (nRF52840) and the Photon 2 (RTL872x). You must not exceed 3.3V on any GPIO pin, including ports such as serial, I2C, and SPI.

SPI

Both the Photon and Photon 2 have two SPI ports, however the pins are different for primary SPI, which is on the S pins on the Photon 2 instead of the A pins on the Photon.

SPI1 on the D pins is the same between the Photon and Photon 2.

Photon Pin Name Photon SPI Photon 2 Pin Name Photon 2 SPI
A2 SPI (SS) A2 / D13  
A3 SPI (SCK) D0 / A3  
A4 SPI (MISO) D1 / A4  
A5 SPI (MOSI) A5 / D14  
D2 SPI1 (MOSI) D2 SPI1 (MOSI)
D3 SPI1 (MISO) D3 SPI1 (MISO)
D4 SPI1 (SCK) D4 SPI1 (SCK)
D5 SPI1 (SS) D5 SPI1 (SS)
    MISO / D16 SPI (MISO)
    MOSI / D15 SPI (MOSI)
    S3 / D18 SPI (SS)
    SCK / D17 SPI (SCK)

SPI - Gen 2 devices (including Photon)

SPI SPI1
Maximum rate 30 MHz 15 MHz
Default rate 15 MHz 15 MHz
Clock 60 MHz 30 MHz
  • Available clock divisors: 2, 4, 8, 16, 32, 64, 128, 256

SPI - Photon 2

SPI SPI1
Maximum rate 25 MHz 50 MHz
Hardware peripheral RTL872x SPI1 RTL872x SPI0

I2C

Both the Photon and Photon 2 have a single I2C port on the same pins, D0/D1.

Photon Pin Name Photon I2C Photon 2 Pin Name Photon 2 I2C
A3   D0 / A3 Wire (SDA)
A4   D1 / A4 Wire (SCL)
D0 Wire (SDA) D0 / A3 Wire (SDA)
D1 Wire (SCL) D1 / A4 Wire (SCL)
  • The Photon 2 I2C port is not 5V tolerant
  • The Photon 2 A3/A4 pins are physically in the same location as D0/D1.
  • The Photon pins A3/A4 are D16/D15 on the Photon 2.

Serial (UART)

The primary UART serial (Serial1) is on the TX and RX pins on both the Photon and Photon 2. There is no hardware flow control on this port on the Photon or Photon 2.

The secondary UART serial (Serial2) is on different pins, however it does not conflict with the RGB LED, and also supports CTS/RTS hardware flow control.

Photon Pin Name Photon Serial Photon 2 Pin Name Photon 2 Serial
D2   D2 Serial2 (RTS)
D3   D3 Serial2 (CTS)
D4   D4 Serial2 (TX)
D5   D5 Serial2 (RX)
    MISO / D16 Serial3 (RX)
    MOSI / D15 Serial3 (TX)
RGBB Serial2 (RX)    
RGBG Serial2 (TX)    
RX Serial1 (RX) RX / D9 Serial1 (RX)
    SCK / D17 Serial3 (RTS)
TX Serial1 (TX) TX / D8 Serial1 (TX)
WKP / A7   D10 / WKP Serial3 (CTS)
Photon Photon 2
Buffer size 64 bytes 2048 bytes
7-bit mode
8-bit mode
9-bit mode
1 stop bit
2 stop bits
No parity
Even parity
Odd parity
Break detection
LIN bus support
Half duplex
CTS/RTS flow control 1

1CTS/RTS flow control only on Serial2. It is optional.

Supported Baud Rates:

Baud Rate P1 P2
110
300
600
1200
2400
4800
9600
14400
19200
28800
38400
57600
76800
115200
128000
153600
230400
500000
921600
1000000
1382400
1444400
1500000
1843200
2000000
2100000
2764800
3000000
3250000
3692300
3750000
4000000
6000000

Analog input (ADC)

For analog to digital conversion (ADC) using analogRead(), there are fewer ADC inputs on the Photon 2:

Photon Pin Name Photon ADC Photon 2 Pin Name Photon 2 ADC
A0 A0 / D11
A1 A1 / D12
A2 A2 / D13
A3 D0 / A3
A4 D1 / A4
A5 A5 / D14
D0   D0 / A3
D1   D1 / A4
DAC / A6    
WKP / A7 D10 / WKP  

On the Photon 2, there are no pins A3 (hardware pin 21) and A4 (hardware pin 22); these are NC (no connection). However, Photon 2 pin D0 (hardware pin 36) can be used as an analog input and has the alias A3. The same is true for Photon 2 pin D1 (hardware pin 35), which has the alias A4.

The setADCSampleTime() function is not supported on the Photon 2 or P2.

PWM (Pulse-width modulation)

The pins that support PWM are different on the Photon and Photon 2.

Photon Pin Name Photon PWM Photon 2 Pin Name Photon 2 PWM
A2   A2 / D13
A3   D0 / A3
A4 D1 / A4
A5 A5 / D14
D0 D0 / A3
D1 D1 / A4
D2 D2  
D3 D3  
    MISO / D16
    MOSI / D15
RX RX / D9  
TX TX / D8  
WKP / A7 D10 / WKP  

All available PWM pins on the Photon 2 share a single timer. This means that they must all share a single frequency, but can have different duty cycles.

Digital to analog converter (DAC)

The Photon supports DAC one A3 and A6 (DAC). There is no DAC on the Photon 2 or Gen 3 devices.

If you need a DAC, it's easy to add one via I2C or SPI on your base board.

Photon Pin Name Photon DAC Photon 2 Pin Name Photon 2 DAC
A3 D0 / A3  
DAC / A6    

WKP (A7)

Photon Photon 2
Module Pin 30 30
Pin Name WKP WKP
A7 D11
Analog Input  
PWM  

On Gen 2 devices (STM32), only the WKP pin can wake from HIBERNATE sleep mode.

This restriction does not exist on the Photon 2 and Gen 3 devices; any pin can be used to wake from all sleep modes.

CAN (Controller Area Network)

The Photon supports CAN on pins D1 and D2. There is no CAN on the Photon 2 or Gen 3 devices (except the Tracker).

  • 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 the Photon 2.
Photon Pin Name Photon CAN Photon 2 Pin Name Photon 2 CAN
D1 D1 / A4  
D2 D2  

I2S (Sound)

The Photon theoretically had I2S sound available on pins D1 and D2, however there has never been support for it in Device OS.

There is no software support for I2S on the Photon 2 either, and while the RTL872x hardware supports I2S, the pins that it requires are in use by other ports.

Photon Pin Name Photon I2S Photon 2 Pin Name Photon 2 I2S
D2 I2S3_SD D2  
D4 I2S3_SCK D4  
D5 I2S3_WS D5  
SETUP I2S3_MCK    

BLE (Bluetooth LE)

BLE Central Mode on the P2 and Photon 2 is only supported in Device OS 5.1.0 and later. Earlier versions only supported BLE Peripheral Mode.

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.

Pin Pin Name Description MCU
15 TX / D8 Low at boot triggers ISP flash download PA[7]
22 D6 SWCLK. 40K pull-down at boot. PB[3]
23 D7 SWDIO. 40K pull-up at boot. Low at boot triggers MCU test mode. PA[27]

Interrupts

There are many limitations for interrupts on the STM32F205. All pins can be used for interrupts on Gen 3 devices and the Photon 2.

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 Photon 2, the internal pull is approximately 2.1K.
  • On the Photon (Gen 2), the internal pull is approximately 40K.

Retained memory

Retained memory, also referred to as Backup RAM or SRAM, that is preserved across device reset, is not available on the Photon 2. This also prevents system usage of retained memory, including session resumption on reset.

On Gen 2 and Gen 3 devices, retained memory is 3068 bytes.

The flash file system can be used for data storage on the Photon 2, however care must be taken to avoid excessive wear of the flash for frequently changing data.

USB

The Photon 2 has a USB C connector, like the Tracker One and Tracker Eval Board.

The Photon has a Micro USB B connector.

Photon Bottom

The Photon 2 has components on both sides of the board, like the Argon. It is not available without the mounted headers, and cannot be reflowed directly to a base board like the Photon without headers.

The Photon 2 does not have the solder pads for the RGB LED and SETUP/MODE button on the bottom. The RGB LED can be directed in software to other pins on the Photon 2. The SETUP/MODE button is available on the header pins on the Photon 2.

Classic Adapter

Classic Adapter

The Particle classic adapter can be used to plug a Photon 2 into a socket that is intended to support an Electron. It can also fit in a Photon socket, however pins will hang past the socket, so there must not be anything in the way, or anything that would short the overhanging pins.

There are many pin limitations, and in particular the classic adapter does not work if you need to use SPI.

Pins B0 - B5 and C0 - C5 are not available if plugging into a Photon socket, as these pins are the pins that hang over the edge and exist only on the Electron, not the Photon

Electron Pin Name Electron Description Photon 2 Pin Name Photon 2 Description
3V3 Regulated 3.3V DC output, maximum load 800 mA. Cannot be used as a power input. 3V3 Regulated 3.3V DC output, maximum load 500 mA
A0 A0 Analog in, GPIO A0 / D11 A0 Analog in, GPIO
A1 A1 Analog in, GPIO A1 / D12 A1 Analog in, GPIO
A2 A2 Analog in, GPIO, SPI SS A2 / D13 A2 Analog in, GPIO, PWM.
A3 A3 True analog out, analog in, GPIO. A5 / D14 A5 Analog in, GPIO, PWM, Was A3 on Gen 3.
A4 A4 Analog in, GPIO, SPI MISO. S4 / D19 S4 GPIO, Was A4 on Gen 3.
A5 A5 Analog in, GPIO, SPI MOSI. A5 / D14 A5 Analog in, GPIO, PWM, Was A3 on Gen 3.
B0 B0, GPIO, PWM   Not Connected
B1 B1, GPIO, PWM   Not Connected
B2 B2, analog in, GPIO, PWM   Not Connected
B3 B3, analog in, GPIO, PWM   Not Connected
B4 B4 Analog in, GPIO   Not Connected
B5 B5 Analog in, GPIO MISO / D16 D16 GPIO, S1 GPIO, PWM, SPI MISO, Serial3 RX.
C0 Serial5 RX (received data), GPIO.   Not Connected
C1 Serial5 TX (trasmitted data), SPI2 MOSI, GPIO.   Not Connected
C2 Serial4 RX (received data), SPI2 MISO, GPIO.   Not Connected
C3 Serial4 TX (transmitted data), SPI2 SCK, GPIO.   Not Connected
C4 I2C, CAN TX, GPIO.   Not Connected
C5 I2C, CAN RX, GPIO. D10 / WKP D10 GPIO. Serial3 CTS. Was D8 on Gen 3.
D0 D0 GPIO, I2C SDA D0 / A3 D0 GPIO, PWM, I2C SDA, A3 Analog In
D1 D0 GPIO, I2C SCL, CAN TX D1 / A4 D1 GPIO, PWM, I2C SCL, A4 Analog In
D2 D2 GPIO, SPI1 MOSI, CAN RX D2 D2 GPIO, Serial2 RTS, SPI1 MOSI
D3 D3 GPIO, SPI1 MISO D3 D3 GPIO, Serial2 CTS, SPI1 MISO
D4 D4 GPIO, SPI1 SCK D4 D4 GPIO, Serial2 TX, SPI1 SCK
D5 D5 GPIO, SPI1 SS D5 D5 GPIO, Serial2 RX, SPI1 SS
D6 D6 GPIO, SWCLK D6 D6 GPIO, SWCLK.
D7 D7 GPIO, Blue LED, SWDIO D7 D7 GPIO, Blue LED, SWDIO
DAC / A6 DAC/A6 True analog out, analog in, GPIO. SCK / D17 SPI SCK, D13 GPIO, S3 GPIO, Serial3 RTS
  Not Connected EN Power supply enable. Connect to GND to power down. Has internal weak (100K) pull-up.
GND Ground. You only need to use one of the Photon ground pins. GND Ground.
  Not Connected LI+ Connected to JST PH LiPo battery connector. 3.7V in or out.
  Not Connected MODE MODE button, has internal pull-up
RST Hardware reset. Pull low to reset; can leave unconnected in normal operation. RST Hardware reset. Pull low to reset; can leave unconnected in normal operation.
RX Serial1 RX (received data), GPIO, PWM. RX / D9 Serial1 RX (received data), GPIO
  Not Connected S3 / D18 S3 GPIO, SPI SS, Was A5 on Gen 3.
TX Serial1 TX (transmitted data), GPIO, PWM. TX / D8 Serial1 TX (transmitted data), GPIO
VBAT Battery for internal real-time clock, jumpered to 3V3.   Not Connected
VIN Power in 3.9V to 12 VDC. Or power out (when powered by USB) 4.8 VDC at 1A maximum. VUSB Power out (when powered by USB) 5 VDC at 1A maximum. Power in with limitations.
WKP / A7 WKP/A7 Wakeup (active high), analog in, GPIO. MOSI / D15 D15 GPIO, S0 GPIO, PWM, SPI MOSI, Serial3 TX

Full module pin comparison

Photon 2 Pinout Diagram
Photon Pinout Diagram

3V3

Photon Photon 2
Pin Name 3V3 3V3
Description Regulated 3.3V DC output, maximum load 100 mA. Or input 3.0V to 3.6V. Regulated 3.3V DC output, maximum load 500 mA

A0

Photon Photon 2
Pin Name A0 A0
Pin Alternate Name n/a D11
Description A0 Analog in, GPIO A0 Analog in, GPIO
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports attachInterrupt Yes. D2, A0, and A3 share the same interrupt handler. Yes
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No

A1

Photon Photon 2
Pin Name A1 A1
Pin Alternate Name n/a D12
Description A1 Analog in, GPIO A1 Analog in, GPIO
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports attachInterrupt Yes. D4 and A1 share the same interrupt handler. Yes
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No

A2

Photon Photon 2
Pin Name A2 A2
Pin Alternate Name n/a D13
Description A2 Analog in, GPIO, SPI SS A2 Analog in, GPIO, PWM.
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports analogWrite (PWM) No Yes
Supports tone No Yes
SPI interface SS. Use SPI object. This is only the default SS/CS pin, you can use any GPIO instead. n/a
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K 42K
Input is 5V Tolerant Yes No

A3

Photon Photon 2
Pin Name A3 D0
Pin Alternate Name n/a A3
Description A3 True analog out, analog in, GPIO. D0 GPIO, PWM, I2C SDA, A3 Analog In
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports analogWrite (DAC) Yes No
Supports analogWrite (PWM) No Yes
Supports tone No Yes
SPI interface SCK. Use SPI object. n/a
I2C interface n/a SDA. Use Wire object. Use 1.5K to 10K external pull-up resistor.
Supports attachInterrupt Yes. D2, A0, and A3 share the same interrupt handler. Yes
Internal pull-up or pull-down resistance 40K 22K

A4

Photon Photon 2
Pin Name A4 D1
Pin Alternate Name n/a A4
Description A4 Analog in, GPIO, SPI MISO. D1 GPIO, PWM, I2C SCL, A4 Analog In
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports analogWrite (PWM) Yes. D3 and A4 share the same PWM channel and the PWM duty cycle is set for both. Yes
Supports tone Yes. D3 and A4 share the same PWM channel and only one frequency can be set for both. Yes
SPI interface MISO. Use SPI object. n/a
I2C interface n/a SCL. Use Wire object. Use 1.5K to 10K external pull-up resistor.
Supports attachInterrupt Yes. D1 and A4 share the same interrupt handler. Yes
Internal pull-up or pull-down resistance 40K 22K
Input is 5V Tolerant Yes No

A5

Photon Photon 2
Pin Name A5 A5
Pin Alternate Name n/a D14
Description A5 Analog in, GPIO, SPI MOSI. A5 Analog in, GPIO, PWM, Was A3 on Gen 3.
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes Yes
Supports analogWrite (PWM) Yes. D2 and A5 share the same PWM channel and the PWM duty cycle is set for both. Yes
Supports tone Yes. D2 and A5 share the same PWM channel and only one frequency can be set for both. Yes
SPI interface MOSI. Use SPI object. n/a
Supports attachInterrupt No Yes
Internal pull-up or pull-down resistance 40K 42K
Input is 5V Tolerant Yes No

D0

Photon Photon 2
Pin Name D0 D0
Pin Alternate Name n/a A3
Description D0 GPIO, I2C SDA D0 GPIO, PWM, I2C SDA, A3 Analog In
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead No Yes
Supports analogWrite (PWM) Yes Yes
Supports tone Yes Yes
I2C interface SDA. Use Wire object. Use 1.5K to 10K external pull-up resistor. Is 5V tolerant. SDA. Use Wire object. Use 1.5K to 10K external pull-up resistor.
Supports attachInterrupt No Yes
Internal pull-up or pull-down resistance 40K 22K
Input is 5V Tolerant Yes No

D1

Photon Photon 2
Pin Name D1 D1
Pin Alternate Name n/a A4
Description D0 GPIO, I2C SCL, CAN TX D1 GPIO, PWM, I2C SCL, A4 Analog In
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead No Yes
Supports analogWrite (PWM) Yes Yes
Supports tone Yes Yes
I2C interface SCL. Use Wire object. Use 1.5K to 10K external pull-up resistor. Is 5V tolerant. SCL. Use Wire object. Use 1.5K to 10K external pull-up resistor.
Supports attachInterrupt Yes. D1 and A4 share the same interrupt handler. Yes
CAN interface CAN2_TX n/a
Internal pull-up or pull-down resistance 40K 22K
Input is 5V Tolerant Yes No

D2

Photon Photon 2
Pin Name D2 D2
Description D2 GPIO, SPI1 MOSI, CAN RX D2 GPIO, Serial2 RTS, SPI1 MOSI
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogWrite (PWM) Yes. D2 and A5 share the same PWM channel and the PWM duty cycle is set for both. No
Supports tone Yes. D2 and A5 share the same PWM channel and only one frequency can be set for both. No
UART serial n/a RTS. Use Serial2 object. Flow control optional.
SPI interface MOSI. Use SPI1 object. MOSI. Use SPI1 object.
Supports attachInterrupt Yes. D2, A0, and A3 share the same interrupt handler. Yes
CAN interface CAN2_RX n/a
I2S interface I2S3_SD n/a
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No

D3

Photon Photon 2
Pin Name D3 D3
Description D3 GPIO, SPI1 MISO D3 GPIO, Serial2 CTS, SPI1 MISO
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogWrite (PWM) Yes. D3 and A4 share the same PWM channel and the PWM duty cycle is set for both. No
Supports tone Yes. D3 and A4 share the same PWM channel and only one frequency can be set for both. No
UART serial n/a CTS. Use Serial2 object. Flow control optional.
SPI interface MISO. Use SPI1 object. MISO. Use SPI1 object.
Supports attachInterrupt Yes. D3 and DAC/A6 share the same interrupt handler. Yes
Internal pull-up or pull-down resistance 40K. Pull-up applied in bootloader for JTAG. 2.1K
Input is 5V Tolerant Yes No
JTAG interface JTAG RST. 40K pull-up at boot. n/a
Signal used at boot JTAG RST. 40K pull-up at boot. n/a

D4

Photon Photon 2
Pin Name D4 D4
Description D4 GPIO, SPI1 SCK D4 GPIO, Serial2 TX, SPI1 SCK
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
UART serial n/a TX. Use Serial2 object.
SPI interface SCK. Use SPI1 object. SCK. Use SPI1 object.
Supports attachInterrupt Yes. D4 and A1 share the same interrupt handler. Yes
I2S interface I2S3_SCK n/a
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No
JTAG interface JTAG TDO. Floating at boot. n/a
Signal used at boot JTAG TDO. Floating at boot. n/a

D5

Photon Photon 2
Pin Name D5 D5
Description D5 GPIO, SPI1 SS D5 GPIO, Serial2 RX, SPI1 SS
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
UART serial n/a RX. Use Serial2 object.
SPI interface SS. Use SPI1 object. Can use any pin for SPI1 SS/CS however. SS. Use SPI1 object. Can use any pin for SPI1 SS/CS however.
Supports attachInterrupt Yes Yes
I2S interface I2S3_WS n/a
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No
JTAG interface JTAG TDI. 40K pull-up at boot. n/a
Signal used at boot JTAG TDI. 40K pull-up at boot. n/a

D6

Photon Photon 2
Pin Name D6 D6
Description D6 GPIO, SWCLK D6 GPIO, SWCLK.
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K. Pull-up applied in bootloader for JTAG. 42K
Input is 5V Tolerant Yes No
JTAG interface JTAG TCK. 40K pull-down at boot. n/a
SWD interface SWCLK. 40K pull-down at boot. SWCLK. 40K pull-down at boot.
Signal used at boot JTAG TCK/SWCLK. 40K pull-down at boot. SWCLK. 40K pull-down at boot.

D7

Photon Photon 2
Pin Name D7 D7
Description D7 GPIO, Blue LED, SWDIO D7 GPIO, Blue LED, SWDIO
Supports digitalRead Yes. But the on-board LED will light when 3.3V is supplied on this pin as well. Yes.
Supports digitalWrite Yes. Note that this controls the on-board blue LED. Yes. On the Photon this is the blue D7 LED.
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K. Pull-up applied in bootloader for JTAG. 2.1K
JTAG interface JTAG TMS. 40K pull-up at boot. n/a
SWD interface SWDIO. 40K pull-up at boot. SWDIO. 40K pull-up at boot.
Signal used at boot JTAG TMS/SWDIO. 40K pull-up at boot. SWDIO. 40K pull-up at boot. Low at boot triggers MCU test mode.

DAC

Removed from Photon
Pin Name DAC
Pin Alternate Name A6
Description DAC/A6 True analog out, analog in, GPIO.
Supports digitalRead Yes
Supports digitalWrite Yes
Supports analogRead Yes
Supports analogWrite (DAC) Yes
Supports attachInterrupt Yes. D3 and DAC/A6 share the same interrupt handler.
Internal pull-up or pull-down resistance 40K

EN

Added to Photon 2
Pin Name EN
Description Power supply enable. Connect to GND to power down. Has internal weak (100K) pull-up.

GND

Photon Photon 2
Pin Name GND GND
Description Ground. You only need to use one of the Photon ground pins. Ground.

LI+

Added to Photon 2
Pin Name LI+
Description Connected to JST PH LiPo battery connector. 3.7V in or out.

MISO

Added to Photon 2
Pin Name MISO
Pin Alternate Name D16
Description D16 GPIO, S1 GPIO, PWM, SPI MISO, Serial3 RX.
Supports digitalRead Yes
Supports digitalWrite Yes
Supports analogWrite (PWM) Yes
Supports tone Yes
UART serial RX. Use Serial3 object.
SPI interface MISO. Use SPI object.
Supports attachInterrupt Yes
Internal pull-up or pull-down resistance 2.1K

MODE

Added to Photon 2
Pin Name MODE
Description MODE button, has internal pull-up

MOSI

Added to Photon 2
Pin Name MOSI
Pin Alternate Name D15
Description D15 GPIO, S0 GPIO, PWM, SPI MOSI, Serial3 TX
Supports digitalRead Yes
Supports digitalWrite Yes
Supports analogWrite (PWM) Yes
Supports tone Yes
UART serial TX. Use Serial3 object.
SPI interface MOSI. Use SPI object.
Supports attachInterrupt Yes
Internal pull-up or pull-down resistance 2.1K

RGBB

Removed from Photon
Pin Name RGBB
Description RGB LED Blue
UART serial RX. Use Serial2 object.
Input is 5V Tolerant No, if LED is connected.

RGBG

Removed from Photon
Pin Name RGBG
Description RGB LED Green
UART serial TX. Use Serial2 object.
Input is 5V Tolerant No, if LED is connected.

RGBR

Removed from Photon
Pin Name RGBR
Description RGB LED Red
Input is 5V Tolerant No, if LED is connected.

RST

Unchanged between Photon and Photon 2
Pin Name RST
Description Hardware reset. Pull low to reset; can leave unconnected in normal operation.

RX

Photon Photon 2
Pin Name RX RX
Pin Alternate Name n/a D9
Description Serial1 RX (received data), GPIO, PWM. Serial1 RX (received data), GPIO
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogWrite (PWM) Yes No
Supports tone Yes No
UART serial RX. Use Serial1 object. RX. Use Serial1 object.
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K 42K
Input is 5V Tolerant Yes No

S3

Added to Photon 2
Pin Name S3
Pin Alternate Name D18
Description S3 GPIO, SPI SS, Was A5 on Gen 3.
Supports digitalRead Yes
Supports digitalWrite Yes
SPI interface Default SS for SPI.
Supports attachInterrupt Yes
Internal pull-up or pull-down resistance 2.1K

S4

Added to Photon 2
Pin Name S4
Pin Alternate Name D19
Description S4 GPIO, Was A4 on Gen 3.
Supports digitalRead Yes
Supports digitalWrite Yes
Supports attachInterrupt Yes
Internal pull-up or pull-down resistance 22K. No internal pull up or pull down in HIBERNATE sleep mode.

SCK

Added to Photon 2
Pin Name SCK
Pin Alternate Name D17
Description SPI SCK, D13 GPIO, S3 GPIO, Serial3 RTS
Supports digitalRead Yes
Supports digitalWrite Yes
UART serial RTS. Use Serial3 object. Flow control optional.
SPI interface SCK. Use SPI object.
Supports attachInterrupt Yes
Internal pull-up or pull-down resistance 2.1K

SETUP

Removed from Photon
Pin Name SETUP
Description SETUP button, has internal pull-up. Pin number constant is BTN.
I2S interface I2S3_MCK

TX

Photon Photon 2
Pin Name TX TX
Pin Alternate Name n/a D8
Description Serial1 TX (transmitted data), GPIO, PWM. Serial1 TX (transmitted data), GPIO
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogWrite (PWM) Yes No
Supports tone Yes No
UART serial TX. Use Serial1 object. TX. Use Serial1 object.
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K 42K
Input is 5V Tolerant Yes No
Signal used at boot n/a Low at boot triggers ISP flash download

USBDATA-

Removed from Photon
Pin Name USBDATA-
Description USB Data-
Input is 5V Tolerant Yes

USBDATA+

Removed from Photon
Pin Name USBDATA+
Description USB Data+
Input is 5V Tolerant Yes

VBAT

Removed from Photon
Pin Name VBAT
Description Battery for internal real-time clock, backup registers, and SRAM. Supply 1.65VDC to 3.6 VDC at 19 μA..

VIN

Removed from Photon
Pin Name VIN
Description Power in 3.6V to 5.5 VDC. Or power out (when powered by USB) 4.8 VDC at 1A maximum.

VUSB

Added to Photon 2
Pin Name VUSB
Description Power out (when powered by USB) 5 VDC at 1A maximum. Power in with limitations.
Input is 5V Tolerant Yes

WKP

Photon Photon 2
Pin Name WKP D10
Pin Alternate Name A7 WKP
Description WKP/A7 Wakeup (active high), analog in, GPIO. D10 GPIO. Serial3 CTS. Was D8 on Gen 3.
Supports digitalRead Yes Yes
Supports digitalWrite Yes Yes
Supports analogRead Yes n/a
Supports analogWrite (PWM) Yes No
Supports tone Yes No
UART serial n/a CTS. Use Serial3 object. Flow control optional.
Supports attachInterrupt Yes Yes
Internal pull-up or pull-down resistance 40K 2.1K
Input is 5V Tolerant Yes No

Software

Wi-Fi Configuration

The Photon 2 and Argon utilize BLE for configuration of Wi-Fi rather than the SoftAP approach taken with the P1. Using BLE allow mobile apps to more easily set up the device Wi-Fi without having to modify the mobile device's network configuration.

Feature Photon 2 Photon Argon
Wi-Fi (SoftAP)
BLE

User firmware binary size

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

Flash file system

On the Photon 2, P2, and Gen 3 devices, there is a flash file system (2 MB) for storing user data. This is not available on Gen 2 devices including the Photon.

Combined and resumable OTA

On the Photon 2, P2, and Gen 3 devices, 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.

Increased API field limits

The maximum size of a variable, function parameter, or publish is 1024 bytes on the Photon 2 vs. 864 bytes on Photon.

API Field Photon Photon 2
Variable Key 64 64
Variable Data 864 1024
Function Key 64 64
Function Argument 864 1024
Publish/Subscribe Event Name 64 64
Publish/Subscribe Event Data 864 1024

Platform ID

The Platform ID of the Photon 2 will different from that of the Photon (6) because of the vastly different hardware.

If you have a product based on the Photon, you will need to create a separate product for devices using the Photon 2. 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 that use peripherals that are not present (such as DAC)
  • Libraries for MCU-specific features (such as ADC DMA)
  • Libraries that are hardcoded to support only certain platforms by their PLATFORM_ID

Version History

Revision Date Author Comments
pre 2022-03-02 RK Pre-release
2022-03-14 RK Minor edits; no functional changes
2022-04-12 RK Added serial baud rates
2022-04-16 RK Major changes to pinmap to align with P2
2022-08-12 RK Added listing of pins used at boot
2022-08-12 RK Warning about BLE central mode not available