1. Dictionary

  • XiPU - XiRX Processor Unit. The name of the 8-bit TTL CPU.
  • XiPU_v2 - The second iteration of the XiPU.
  • XiPC - XiRX Personal Computer. The name of the simple computer based on XiPU CPU
  • TTL - Transistor-transistor logic.
  • HCT - High-Speed CMOS chips available in TTL compatible form.
  • RAM - Volatile random access memory.
  • ROM - Non-volatile read-only memory.
  • Register - Quickly accessible location for a small amount of data stored in a TTL chip.
  • uROM - uROM determines which of the internal registers is used to read from and write to at the current micro step of executing instruction.
  • BIOS - Basic input/output system. Provides access to basic IO API and loads the OS.
  • OS - Operating System. It contains a terminal interface and basic libraries.
  • Stack - High accessibly memory page where data is stored as FILO.
  • Function Frame - Part of the stack where arguments of the function and local variables are stored.
  • IO operation - Read or write data to pins connected to external world.
  • External BUS - Data highway for IO operations.
  • ALU - Arithmetic logic unit.

2. XiPU_v2

  • 8-bit processor based on 7400 HCT chips compatible with TTL.
  • 64 kB of RAM space. Lower 2 kB are reserved for BIOS stored at EEPROM. The 4 kB at the end of the memory are used as a stack. Rest 58 kB of memory could be used by OS or applications.
  • 1 MHz clock speed. The processor uses a 2 MHz crystal to get two 1 MHz square waves shifted relative to the other about half.
  • The processor uses uROM stored in two EEPROMs.
  • Each instruction could be built from 2 to 16 micro steps. Each micro step takes exactly 1 clock tick.
  • Four registers:
    • A, B - 8-bit general purpose registers.
    • X, Y - 8-bit auxiliary registers. Could be used mostly as general purpose registers. Together, it can be used as a 16-bit address register.
  • Two hidden stack registers:
    • SP - Stack Pointer. It is used to address the head of the stack.
    • BP - Base Pointer. It is used to address the function frame on the stack to store parameters of a function and local variables.
  • Three internal buses:
    • BUS A - 8-bit main BUS for registers, RAM, ROM, IO operations.
    • BUS B - 8-bit auxiliary BUS for registers used as second input for ALU.
    • BUS C - 16-bit memory address BUS for addressing RAM.
  • 8-bit IN and 8-bit OUT external data BUS. It is used as a simple communication way with the external word.

3. XiPC

  • Personal computer based on the XiPU.
  • 40x30 characters with 16 colors support. It uses 640x480 LCD with an 8-bit color palette to render image output.
  • Mono speaker with a volume knob.
  • RS-232 with 1200 bps support.
  • RTC with battery support.
  • Built-in QWERTY keyboard.
  • 4 status LEDs.
  • 7.5V max 1.0A power supply.

4. Links