We first heard about the Adafruit “Grand Central” board back in the middle of August. First teased on Adafruit’s “Ask An Engineer,” the new board looks a lot like the old Arduino MEGA and shares the same footprint and pinout of the now venerable board. But that’s where the similarities stop.
The Grand Central M4 has been made possible by Microchip’s SAM D51 processor, a 32-bit Arm Cortex-M4 running at 120 MHz, as it is the first in the range to come in a 128-pin package, and that’s enough pins to build a MEGA-like board.
Like the old MEGA, the left-hand side of the board shares the normal Uno pinout, which means that normal Arduino, and Metro, shields will work with the new board as power, analog, and hardware SPI, I2C, and UART are all where you’d expect them.
However the new ATSAMD51P20 processor means that the new board comes with things that the old MEGA, built around the now aging Microchip ATmega2560, didn’t — including hardware DSP and floating point support, a 12-bit parallel capture controller supporting camera and video input, and a built-in crypto engine with AES (256 bit), true RNG, and a Pubkey controller.
While the board itself will operate at a 3.3V logic level you’ll be able to power it either through the 7–9 V polarity protected DC jack, or via the micro-USB. The board has 62 GPIO pins, 16 of which are analog in, and 2 are “true” analog out. There is hardware SPI, I2C, and UART, along with 5 more serial ports available.
The board has native USB, and like the old Arduino Leonardo it can act as a USB HID keyboard or mouse. There are also four indicator LEDS—one green power LED, two RX/TX LEDs for data being sent over USB, and a red connected LED—as well as on NeoPixel on the front edge of the PCB.
Removable storage is provided by a micro SD card slot connected to an SPI, and the on board 8 MB QSPI Flash storage. When you’re using the board with CircuitPython this Flash storage is used as a “very tiny hard drive” for our scripts, libraries and files. However it is also accessible if you’re using the board as an Arduino, appearing much like another external SD card.
The board will be supported by both the Arduino environment, but similar to most modern Adafruit boards, is primarily intended to be used with CircuitPython.
UPDATE: It looks like Adafruit has changed the board’s color, now a fetching grey, to match the rest of the Metro family.