ArduinoPC

Arduino Nano Personal Computer - Squeezing Water from a Stone

I am pushing the limits of how much compute you can get out of an Arduino Nano:

    o 320x200 pixels of monochrome VGA output (optional: 16 row colors)

    o PS/2 keyboard readout

    o requires only 1(!) logic IC 74HC166

HOW TO USE THE 'NANO HOME COMPUTER'

1. Set the Nano's fuses for output of the 16MHz system clock on pin D8 (see appendix A below).

2. Copy the library files 'os.h' and 'os.S' into a folder '../Arduino/libraries/os'.

3. Start a new sketch with '#include <os.h>'. The following global variables and functions are available:

    int os::frames                                        built-in 16-bit 60Hz frame counter
   
    byte os::vram[25][40]                                 character video RAM array
   
    byte os::cram[25]                                     row color RAM array, available colors are:
   
                                                          WHITE, BLACK, GRAY, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN,
                                                
                                                          DKGRAY, DKRED, DKGREEN, DKYELLOW, DKBLUE, DKMAGENTA, DKCYAN.
                                                
    os::text(String s, byte x, byte y, byte col = 0)      prints text at screen position (x, y), col = 0: don't set row color
   
    os::fill(char c = 32)                                 fills the video RAM with character c
   
    os::scroll()                                          scrolls the video RAM one step upwards
   
    os::wait(int n)                                       waits for n frames
   
    byte os::getkey()                                     returns keystroke ASCII code (none: 0)

4. 26KB FLASH (1KB SRAM) of the Nano's 30KB FLASH (2KB SRAM) are usable, respectively. To save SRAM, define constant variables in FLASH memory by adding PROGMEM to the data type. Constant string arguments can be defined in FLASH by using the F("...") macro.

5. Have fun!

APPENDIX

A. Setting Arduino Nano's fuse bytes via ISP (in-situ programming) for output of system CLK

o Connect two Arduino Nanos in the following way (programmer -> target): D13 -> D13, D12 -> D12, D11 -> D11, D10 -> RESET, 5V -> 5V, GND -> GND

o Arduino IDE: Upload sketch 'examples/ArduinoISP' into programmer and select 'Tools/Programmer/Arduino as ISP'.

o Open the file 'C:\Program Files (x86)\Arduino\hardware\arduino\avr\boards.txt'.

o In section '## Arduino Nano w/ ATmega328P' (line 141), change line 149 'nano.menu.cpu.atmega328.bootloader.low_fuses=0xFF' (default) to '...=0xBF' (output system CLK on Pin D8 (B0)) and save the file.

o Close and re-open the Arduino IDE for the changes to become active.

o Select target board: 'Arduino Nano', processor: 'AtMega328P' and 'Tools/Burn bootloader'.

B. Hardware

Pin A0 (C0): keyboard input CLK

Pin A1 (C1): keyboard input DAT

Pin A2-5 (C2-5): 4-bit color output to 74HC08 (optional)

Pin D0-7 (D0-7): 8-bit pixel output to 74HC166

Pin D8 (B0): CLKO (16MHz system clock output)

Pin D9 (B1): unused

Pin D10 (B2): /VSYNC VGA (timer1, every 1/60s)

Pin D11 (B3): /PE 74166 pixel shift register synchroneous parallel load on rising edge of CP

Pin D12 (B4): /HSYNC VGA (inside ISR, every 32µs)

Pin D13 (B5): LED