pins it's mapped to. Unlike other peripherals, you cannot mux these signals to other pins!
DEN1: SDA
DEN2: SCL
CLK: D6
D0: D11
D1: D13
D2: D10
D3: D12
D4: MISO
D5: D5
D6: MOSI
D7: SCK
QSPI Flash and NeoPixel
As part of the 'Express' series of boards, the Feather M4 Express is designed for use with CircuitPython. To make that
easy, we have added two extra parts to this Feather M4: a mini NeoPixel (RGB LED) and a 2 MB QSPI (Quad SPI) Flash
chip
The NeoPixel is connected to pin #8 in Arduino, so just use our NeoPixel library (https://adafru.it/dhw) and set it up as a
single-LED strand on pin 8. In CircuitPython, the NeoPixel is board.NEOPIXEL and the library for it is
here (https://adafru.it/wby) and in the bundle (https://adafru.it/uap). The NeoPixel is powered by the 3.3V power supply
but that hasn't shown to make a big difference in brightness or color. The NeoPixel is also used by the bootloader to
let you know if the device has enumerated correctly (green) or USB failure (red). In CircuitPython, the LED is used to
indicate the runtime status.
The QSPI Flash is connected to 6 pins that are not brought out on the GPIO pads. This way you don't have to worry
about the SPI flash colliding with other devices on the main SPI connection.
QSPI is neat because it allows you to have 4 data in/out lines instead of just SPI's single line in and single line out. This
means that QSPI is
at least
4 times faster. But in reality is at least 10x faster because you can clock the QSPI peripheral
much faster than a plain SPI peripheral
However, the QSPI port is
not
also on an SERCOM. So, you have to either use the QSPI peripheral or bitbang SPI if you
want to talk to the chip. We have an Arduino library here which provides QSPI interfacing for
Arduino (https://adafru.it/BeX). In CircuitPython, the QSPI flash is used natively by the interpretter and is read-only to
user code, instead the Flash just shows up as the writeable disk drive!
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