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Expansion Header




Due to an issue inside the STM32F4 MCU, the JTAG connection will no longer work when GPIO PB4 is used. This is not an problem when using the Lua Development Environment, but can introduce issues when custom Screvle firmware is developed. Alternatively, if PB4 needs to be used, the Serial Wire Debug (SWD) interface can be used instead of JTAG.

5V Tolerance

All except the following pins are 5V tolerant: PA4, PA5 (the pins supporting the DAC peripheral).

Power Pins

3V3 Output

Enabled by default, current is limited to 500mA by a poly-fuse.

5V Output

Disabled by default, current is limited to 500mA by a poly fuse. To enable the 5V output, call the system.enable5V() function:

Example: Enabling 5V output on expansion header


-- Turn on 5V output


Li-Ion Battery Output

The output of the Li-Ion battery charger is available to derive other voltages. The nominal voltage of this pin is 4.35V when externally powered, or the Li-Ion battery voltage when not externally powered.

Coin-Cell Battery Output

Output of the Reatl-Time-Clock backup battery. Should only be used for (low-) power backup.

Power Input

Allows powering Screvle via the expansion header. Supply 5V power.

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