The SparkFun Pro Micro

The Leonardo's chip in a Pro Mini's footprint, with a USB socket on the end, and without the one thing people look for first: an LED on pin 13.

What it is

An ATmega32U4 at 16 MHz and 5 V on a board 33 by 18 mm, with two rows of twelve holes 0.6 inch apart and a micro-USB socket on the short end. It runs the Leonardo's programs and numbers its pins the Leonardo's way. The USB goes to the chip, so Serial is the chip's own USB port (the serial monitor) and Serial1 is the USART on pins 0 and 1.

There is no pin 13

The chip's PC7, which is pin 13 and the L LED on a Leonardo, is not brought out on a Pro Micro. LED_BUILTIN is still 13, so the Blink every tutorial starts with compiles and lights nothing. That is what a real Pro Micro does.

The two lamps the board does have are RX, on PB0 (pin 17, which is also SPI's SS, and has no hole), and TX, on PD5, which has no pin number at all. Both are wired from 5 V through a resistor to the pin, so they light when the pin is driven LOW. The Arduino core has names for the four moves, and so does Mokxi's: TX_RX_LED_INIT sets both pins up, RXLED1 and TXLED1 light the lamps, RXLED0 and TXLED0 put them out. The built-in RX blink program is the blink for this board.

Pins

With the USB at the top, the left row reads TXO (pin 1), RXI (pin 0), GND, GND, then pins 2 to 9. The right row reads RAW, GND, RST, VCC, A3 to A0, then 15, 14, 16 and 10.

• 14, 15 and 16 are SPI's MISO, SCK and MOSI.
• Pins 2 and 3 are I2C's SDA and SCL.
• 3, 5, 6, 9 and 10 do PWM with analogWrite.
• VCC is the 5 V rail and a supply for the breadboard. RAW is the regulator's input and is ignored: the board is always powered.

What is modeled

The Leonardo model's ATmega32U4, whole: core, ports, timers, USART, ADC, interrupts, sleep and the USB serial port as a byte pipe. The RX and TX lamps light from their pins, the way around the board wires them.

What is not modeled

• The USB stack: no enumeration, no keyboard or mouse.
• The 3.3 V, 8 MHz version of the board. This is the 5 V one.
• The regulator: VCC is an ideal 5 V rail.

Starter project

Pro Micro blink blinks the RX lamp, which lights on LOW, and an LED on pin 9 wired the ordinary way around, side by side.