E404X migration guide

This guide assists in the transition from the E-Series E402/E404 to the E404X.

Software differences

User firmware binary size

One major advantage of the E404X is that user firmware binaries can be up to 256 Kbytes, instead of 128 Kbytes on Gen 2 devices including the E-Series.

Flash file system

On the E404X and Gen 3 devices, there is a flash file system (2 MB) for storing user data. This is not available on Gen 2 devices.

Combined and resumable OTA

On the E404X 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 E404X vs. 864 bytes on other E-Series models.

Sleep modes

• In general, the E404X will use less power in all modes.
• In HIBERNATE mode, the RTC (real time clock) does not run on the E404X, so you cannot wake by time from HIBERNATE mode (formerly known as SLEEP_MODE_DEEP).
• However, you can wake by time from ULTRA_LOW_POWER mode, and it uses less power than the E-SeriesHIBERNATE mode.
• On Gen 2 devices, you can only wake from HIBERNATE with a rising signal on WKP (A7). The E404X can wake from HIBERNATE on any pin, rising or falling.
• On Gen 2 (STM32F205) devices, if you try to go into HIBERNATE mode with WKP already high, the device will go into sleep and will not wake up by time or pin change, essentially rendering it unable to wake until reset manually. This problem does not occur on the E404X and Gen 3 devices.

RTC (Real-time clock)

• The E-Series module has the ability to use an external lithium coin cell or supercap to power the RTC when the MCU is unpowered. This feature does not exist on the E404X.
• The RTC on the E404X s is not really a real-time clock. It's basically just a counter, and some advanced wakeup features are not possible on the E404X and Gen 3 devices. These features were not enabled by Device OS on Gen 2 devices, either, so this is generally not an issue.
• On the E404X and Gen 3 devices, in HIBERNATE sleep mode the RTC does not run, so it is not possible to wake by time, and the system clock will not be set until you connect to the cloud again. ULTRA_LOW_POWER is recommended instead.

Hardware differences

MCU

The microcontroller is different in E-Series and E404X:

• ¹Most of this space is reserved by the system and only a portion if it is available to user applications as a flash file system.
• Not all RAM is available to user applications. The Device OS firmware uses a portion of it.

BLE (Bluetooth LE)

• Bluetooth LE (BLE 5.0) is supported on the E404X but not E-Series (Gen 2).

No 5V tolerance!

On Gen 2 devices (STM32F205), most pins are 5V tolerant. This is not the case for the E404X and Gen 3 (nRF52840). You must not exceed 3.3V on any GPIO pin, including ports such as serial, I2C, and SPI.

Pins no longer available for GPIO

You will need to use different pins if you are currently using these pins.

B0 and B1 should not be used as wake sources

• Pins B0 and B1 should not be used as GPIO wake sources.
• In ULP sleep mode, when used as an input B0 and B1 should be held at the same logic level even if not used as a wake source.
• On other devices these pins are used as NFC and the circuitry which protects the MCU from surge voltage can cause leakage voltage between these pins when used as GPIO in both operating and sleep modes.

Beware of leakage current

If you have circuitry that can disconnect the nRF52840 MCU 3V3 power, beware of situations where current can leak into GPIO pins from an external supply.

For example, if you have 3V3 disconnect circuitry but have pull-ups to non-disconnected power, when MCU 3V3 is powered down current can flow into the GPIO causing the MCU to not fully power down. This can prevent the MCU from resetting when power is reapplied. It will also cause excess power consumption when powered down.

SPI

• On the E404X, there are only two SPI ports SPI (A pins) and SPI1 (C pins)
• E-Series SPI1 on the D pins does not exist on the E404X.
• E-Series SPI2 on the C pins is SPI1 on the E404X

The following are all SPI-related pins on the E-Series and E404X:

The following SPI data rates are available:

• Available clock divisors: 2, 4 (default), 8, 16, 32, 64, 128, 256
• On the E404X, SPI_MODE_SLAVE is only supported on SPI1 and is limited to 8 MHz

I2C

• There is one available I2C port on the E404X.

• On the E-Series (other than the E404X), Wire and Wire1 are the same I2C peripheral and you can only use one at a time, so effectively it only has one I2C port.
• On the E-Series (other than the E404X), the built-in pull-up on SDA and SCL is approximately 40K and an external pull-up is required.
• On the E404X, the built-in pull-up on SDA and SCL is approximately 13K. An external pull-up is recommended.
• On the E404X, GPIO is 3.3V and is not 5V tolerant. Connecting to a 5V I2C bus requires level shifting.
• On the E404X, external pull-ups should only be connected to the MCU 3V3 supply. Pulling up to an external supply can cause leakage current into the GPIO pins of the nRF52840 which can prevent it from resetting properly.

Serial (UART)

The primary UART serial (Serial1) is on the TX and RX pins on both the E-Series and E404X. There is no hardware flow control on this port on E-Series, but it can be enabled on the E404X on pins D0 (CTS) and D1 (RTS).

The E-Series has additional serial ports Serial2, Serial4, and Serial5. These are not available on the E404X.

¹Default buffer size is 64 bytes but you can configure a larger buffer if desired, limited by available RAM.

²CTS/RTS flow control optional on Serial1.

Baud rate support

Serial configurations

• Using an I2C or SPI UART like the SC16IS750 is also a good way to add support for other bit length, parity, and stop bit options on Gen 3 devices.

Analog input (ADC)

For analog to digital conversion (ADC) using analogRead(), there are fewer ADC inputs on the E404X:

If additional ADC ports are needed, an external I2C and SPI ADC can be added to your base board.

PWM (Pulse-width modulation)

The pins that support PWM are different on the E-Series and E404X.

PWM on the same timer group (such as TIM3 or PWM3) must share the same frequency, but can have different duty cycles.

On the E404X, the following groups are defined. Each group must share the same frequency and resolution, but individual pins in the group can have a different duty cycle. Group 0 is shared with the RGB LED and must use the default resolution of 8 bits (0-255) and frequency of 500 Hz, but can have its own duty cycle.

• Group 0: C5, RGBB, RGBG, RGBR
• Group 1: A3, C0, D0, D1, D2
• Group 2: B2, B3, RX, TX
• Group 3: A4, A5, A6, C4

Digital to analog converter (DAC)

The E-Series supports DAC one A3 and A6 (DAC). There is no DAC on the E404X or Gen 3 devices.

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

WKP (A7)

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

This restriction does not exist on the E404X and Gen 3 devices; any pin except B0 and B1 can be used to wake from all sleep modes, rising or falling.

CAN (controller area network)

The E series supported CAN on pins D1/D2 or C4/C5. There is no CAN on the E404X 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 E404X.

I2S (Sound)

• The E-Series theoretically had I2S sound available on pins D1 and D2, however there has never been support for it in Device OS.
• I2S is available on Gen 3 devices including the E404X on any GPIO pins using a 3rd-party library.

Interrupts

There are many limitations for interrupts on the E-Series (STM32F205). All pins can be used for interrupts on the E404X Gen 3 devices, however you can only attach interrupts to 8 pins at a time.

SWD

Unlike the E-Series module, the E404X SWD pins are dedicated and cannot be used for GPIO.

JTAG

The E404X does not support full JTAG. Some pins are shared with SWD; the E404X SWD pins are dedicated and cannot be used for GPIO.

Pin D5 (module pin 37), however, is available for GPIO as it is not NC and not used by SWD.

USB

The following USB feature differences exist:

Pin functions removed

The following pins were used on the E-Series but are not available on the E404X. You should not connect anything to these pins.

Pin functions added

No pin functions have been added to previously unused (NC) pins.

Full module pin comparison

Module Pin 1 (VIN)

Module Pin 2 (GND)

Module Pin 3 (VBUS)

Module Pin 4 (GND)

Module Pin 5 (LIPO)

Module Pin 6 (NC)

Module Pin 7 (GND)

Module Pin 8 (PMID)

Module Pin 9 (3V3)

Module Pin 10 (VDDA / NC)

Module Pin 11 (VBAT / NC)

Module Pin 12 (GND)

Module Pin 13 (USBDATA+)

Module Pin 14 (USBDATA-)

Module Pin 15 (GND)

Module Pin 16 (TX)

Module Pin 17 (RX)

Module Pin 18 (GND)

Module Pin 19 (WKP / A7)

Module Pin 20 (DAC / A6)

Module Pin 21 (A5)

Module Pin 22 (A4)

Module Pin 23 (A3)

Module Pin 24 (A2)

Module Pin 25 (A1)

Module Pin 26 (A0)

Module Pin 27 (GND)

Module Pin 28 (B5 / NC)

Module Pin 29 (B4 / NC)

Module Pin 30 (B3)

Module Pin 31 (B2)

Module Pin 32 (B1)

Module Pin 33 (B0)

Module Pin 34 (GND)

Module Pin 35 (D7 / SWDIO)

Module Pin 36 (D6 / SWDCLK)

Module Pin 37 (D5)

Module Pin 38 (D4 / SWO)

Module Pin 39 (D3 / NC)

Module Pin 40 (D2)

Module Pin 41 (D1)

Module Pin 42 (D0)

Module Pin 43 (GND)

Module Pin 44 (C5)

Module Pin 45 (C4)

Module Pin 46 (C3)

Module Pin 47 (C2)

Module Pin 48 (C1)

Module Pin 49 (C0)

Module Pin 50 (NC)

Module Pin 51 (GND)

Module Pin 52 (RGBB)

Module Pin 53 (RGBG)

Module Pin 54 (RGBR)

Module Pin 55 (MODE)

Module Pin 56 (RESET)

Module Pin 57 (STAT)

Module Pin 58 (GND)

Module Pin 59 (GND)

Module Pin 60 (GND)

Software

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

Since the E404X uses the same MCU as Gen 3 devices (Boron, B-Series SoM, Tracker SoM), most libraries intended for those platforms will work with no changes or minimal changes.

Version history