DUO EXECUTIVE

The DUO Executive is an inexpensive computer based on the ATMega328. The computer has black and white VGA output and PS/2 keyboard input. Six female header pins are also available for digital output and analog input.

Files are stored in a 128 KB EEPROM chip. Data may be written and read from a host computer through a serial interface.

All programs on the computer are written in a proprietary language called DEPL (DUO Executive programming language). DEPL consists of plain ASCII commands interpreted by the ATMega328. 600 bytes of RAM are available for DEPL programs.


Parts to use from Mouser

(x2) Microcontroller: ATMEGA328P-PU
(x2) Crystal oscillator: MP160B
(x4) Capacitor: 140-100N2-200J-RC
Serial EEPROM: 25LC1024-I/P
Serial SRAM: 23LC1024-I/P
FIFO: SN74ALS236N
Buffer: SN74LV125ANE4
Resistor (1K ohm): 291-1K-RC
Resistor (10K ohm): 291-10K-RC
Diode: 1N4150TR
Larger capacitor: UVR1H100MDD1TA
Button: PTS645SH50-2 LFS
Switch: EG1218


Parts to use from DigiKey

D-sub connector: 1-1734530-1
Circular connector: MD-60SM
(x2) IC socket (28 pins): 1-390261-9
(x2) IC socket (8 pins): 1-390261-2
IC socket (16 pins): 1-390261-4
IC socket (14 pins): 1-390261-3
Female header (6 pins): PPTC061LFBN-RC
(x2) Female header (8 pins): PPTC081LFBN-RC
Wall adapter: WSU050-1500-R
Barrel connector: PJ-102A


Communicating with the ATMega328 through USB

http://arduino.cc/en/Main/Standalone
https://www.sparkfun.com/products/718
USB interface chip: FT232RL-REEL


ATMega328 pin connections

Pin 0: RX
Pin 1: TX
Pin 2: EEPROM CS
Pin 3: SRAM CS
Pin 4: EEPROM + SRAM SCK
Pin 5: EEPROM + SRAM SI
Pin 6: EEPROM + SRAM SO and VGA intensity
Pin 7: VGA SCK OE
Pin 8: VGA VSYNC
Pin 9: FIFO RST (necessary during power on)
Pin 10: FIFO SO
Pin 11: FIFO Q0
Pin 12: FIFO OR
Pin 13: Device mode (VGA or serial)
Pins 14-19: Program controllable


VGA Pin connections

GND  X  BLUE GREEN RED

  GND  PWR  GND   GND   GND

X  VSYNC HSYNC  X    X

(front of female VGA connector)

Sources for timing:
http://www.javiervalcarce.eu/wiki/VGA_Video_Signal_Format_and_Timing_Specifications
http://tinyvga.com/vga-timing/640x480@60Hz
http://www.pyroelectro.com/tutorials/arduino_basic_vga/
http://garagelab.com/profiles/blogs/arduino-generated-vga-color-signal-complete


File allocation table

Each entry will be 32 bytes long. There will be a maximum of 128 entries occupying the first 4 KB of EEPROM.

Entry format:

[2 byte name length] [14 byte name characters] [2 byte file size] [2 byte type length] [6 byte type characters] [4 byte file address] [2 byte unused gap]

If an entry is unused, the file size will be 0x0000 or 0xFFFF.


Variable allocation table

Each entry will be 14 bytes long.

Entry format:

[1 byte name length] [8 byte name characters] [1 byte variable type] [2 byte variable size] [2 byte variable address]

If an entry is unused, the variable size will be 0.


NOTES TO SELF:

- Connect SRAM to VGA connector through a buffer.
- Source the PS/2 clock with a 1K ohm resistor and use an inverter.
- EEPROM must be sent a write enable command before EVERY write operation.
- Add grounded diode between SRAM and microcontroller to prevent flurries.