Skip to content

Hardware Guide

Jump to bottom
Chris Vig edited this page Sep 1, 2025 · 3 revisions

SuperKey Hardware Guide

This guide describes the SuperKey's hardware.

PCB Layout

The general layout of the current prototype hardware is shown below:

pcb_layout

Microcontroller

The SuperKey uses an ATmega1284P microcontroller, currently produced by Microchip Technology. The datasheet for the ATmega1284P is available at this link. The microcontroller uses a dual inline package (DIP) configuration, since this is the easiest type of integrated circuit for hobbyists to work with.

The microcontroller has the following resources:

  • 128 kilobytes Flash memory (program data)
  • 4 kilobytes EEPROM memory (non-volatile storage)
  • 16 kilobytes static RAM
  • 32 GPIO lines
  • 4 hardware timers / counters
  • 2 USARTs
  • I2C interface
  • SPI interface
  • 8-channel, 10-bit ADC

Pinout

The pinout for the ATmega1284P is shown below:

pinout

Pin Assignments

The current pin assignments are shown in the table below. Pins which are not listed are currently unassigned.

Pin Function Description Notes
6 MOSI SPI Controller Out Only used for programming
7 MISO SPI Controller In Only used for programming
8 SCK SPI Clock Only used for programming
9 RESET Reset Device
10 VCC Power
11 GND Ground
12 XTAL2 Crystal Oscillator Input 2
13 XTAL1 Crystal Oscillator Input 1
14 RXD0 Interface Port UART RX
15 TXD0 Interface Port UART TX
16 RXD1 Debug Port UART RX
17 TXD1 Debug Port UART TX
19 OC1A Buzzer Output
20 PD6 Key LED Active high
21 PD7 Status LED Active high
30 AVCC ADC Power ADC is currently unused
31 GND Ground
32 AREF ADC Reference Voltage ADC is currently unused
33 PA7 Output TRS Ring
34 PA6 Output TRS Tip
35 PA5 Input TRS 2 Ring
36 PA4 Input TRS 2 Tip
37 PA3 Input TRS 1 Ring
38 PA2 Input TRS 1 Tip
39 PA1 Input TRS 0 Ring
40 PA0 Input TRS 0 Tip

Clock

The device uses a crystal oscillator with a frequency of 16 MHz as its primary clock inputs. This is connected to the XTAL1 and XTAL2 pins as shown in the schematic. The capacitors are 22 pF.

xtal

Fuses

The microcontroller fuse configuration was calculated using this site. The fuses are set for the following options:

  • External Crystal Oscillator
    • Frequency 8.0+ MHz
    • Start-up time 16K clocks + 0 ms
  • Enable SPI programming
  • Enable JTAG
  • Enable brown-out detection at 2.7 V

This leads to the following fuse bytes:

  • Low: 0xDF
  • High: 0x99
  • Extended: 0xFD

The fuses can be programmed with the following avrdude command:

avrdude -c avrispmkii -P usb -p m1284p -U lfuse:w:0xdf:m -U hfuse:w:0x99:m -U efuse:w:0xfd:m

Clone this wiki locally