Design documents:

Overall block diagram
    v1.0, 3 April 2002
    v1.1, 3 April 2002
    v1.2, 22 April 2002

Detailed schematic diagrams
    Schematic of 26 April 2002
    Schematic of 23 April 2002

Layout
    Check plot of 26 April 2002
    Parts footprints of 23 April 2002

Bill of materials
    Parts list of 26 April 2002

Microcontroller
    80C51 family architecture
    80C51 family programming manual
    80C51 family instruction set
    80C51 family hardware manual
    extended architecture 80251 programming manual
 

Bus timing, 4 April 2002

Data sheets
    T89C51RC2 Microcontroller
    TL16C754 Quad UART
    RC6850 Voice Synthesizer Chipset
    MAX233A RS232 interface
    MAX6818 Switch debounce for button box
    74C161 Counter for system clock

I/O details
    PC Serial port pinout data
    PC serial port registers, etc.
    PC enhanced parallel port