The Arduino Micro

The Leonardo's ATmega32U4, shrunk onto a board that pushes into a breadboard.

What it is

An ATmega32U4 at 16 MHz on a board 48 by 18 mm, with two rows of seventeen holes 0.6 inch apart. It is the same chip as the Leonardo with the same pin numbers, so a sketch and a program built for one run on the other unchanged. The USB goes to the chip itself: Serial is the chip's own USB port, which is what the serial monitor shows, and Serial1 is the USART on pins 0 and 1.

Pins

With the USB at the top, the left row reads 13, 3V3, AREF, A0 to A5, two NC holes, 5V, RST, GND, VIN, MISO and SCK. The right row reads 12 down to 2, GND, RST, RX (pin 0), TX (pin 1), SS and MOSI.

• Pin 13 has the L LED, as on the Leonardo.
• MISO, SCK, MOSI and SS are pins 14 to 17. The Leonardo only has them on its ICSP header; the Micro gives them holes of their own.
• SS is also the RX lamp's pin, PB0. The lamp hangs from 5 V, so driving SS low lights it. RXLED1 and RXLED0 do that from a sketch, and TXLED1 and TXLED0 light the TX lamp on PD5, which has no hole.
• The two NC holes are connected to nothing.
• SDA and SCL are pins 2 and 3, not A4 and A5: on this chip I2C is on port D.
• The two RST holes are one trace.

What is modeled

Everything the Leonardo model does: the ATmega32U4's core, five ports, four timers including the ten-bit timer 4, the USART, fourteen ADC channels, external interrupts and sleep, and the USB serial port as a byte pipe to the monitor. The L, RX, TX and ON lamps light from the pins behind them.

What is not modeled

The USB stack itself: Serial is a pipe to the monitor, with no enumeration and no USB descriptors, and the chip cannot pretend to be a keyboard or a mouse. Everything the Leonardo leaves out is left out here too.

Starter project

Micro blink is the board across a breadboard running the Leonardo's RX blink: the RX lamp and an LED on pin 9 flash together, so you can see that the LED is lit by driving its pin HIGH and the lamp by driving its pin LOW.