A7

A hand-made computer based on a 8-bit PIC18F26K22 microcontroller.

Specifications

CPU

• 64MHz PIC18 core (up to 16MIPS).
• 3896 RAM bytes.
• 32768 16-bit instruction words.

Display

• 128x64 STN display with white pixels on blue backlight.
• 8-bit data interface with the microcontroller.

Input

• Standard PS/2 keyboard support.
• Connect via standard PS/2 6-pin mini DIN connector.

External storage

• On-board 128KB EEPROM (256-byte pages, 6ms maximum to write a page).
• Connected to a fast 4MHz SPI bus (less than 600us to read a full 256-byte page).

Communication

• Standard RS-232 DB9 connector.
• Communication settings : 115200 bauds, no parity, one stop bit.

Power supply

• Standard power supply jack.
• Input voltage from 7V to 24V with at least 200mA.
• Polarity reversal protection.

Hardware

Schematics and PCB have been made with Eagle 7.5.

Software

Use Microchip XC8 compiler to build software.
You have to add the following environment variable for the build system to find the compiler-provided include files :

XC8_INCLUDES_PATH

The variable content must be the full path to the XC8 include directory. Below is an example for a Windows machine (don’t forget to add quotation marks if the path contains spaces) :

"C:\Program Files\Microchip\xc8\v1.42\include"

In order to download applications on the A7, you have to set the following environment variable with the serial port device used to communicate with the A7 (like /dev/ttyS0, /dev/ttyUSB0…) :

A7_APPLICATION_DOWNLOAD_SERIAL_PORT_DEVICE

Casing

Casing panels have been drawn with LibreCAD.

Photo gallery

128x64 pixels graphical display

Casing assembly

Other viewing angles

Booted operating system