Welcome to the section dedicated to seb80, my custom computer based on the Z80 processor and built using 7400-series TTL ICs.
I designed and built seb80 from basic components (CPU, RAM, ROM, etc.), to learn about how computers work, at a more fundamental (organization, architecture, interfacing) level.
seb80 has a 16-bit address bus (64 kilobytes addressable directly), and an 8-bit data bus.
CPU: Zilog (or clone) Z80, model number Z84C0020PEC (CMOS)
Clock: manual or up to few megahertz (removable DIP 14 oscillator)
ROM: IC model 27256 or compatible (32 kilobytes), real addresses 0000-7FFF
RAM: IC model 62256 or compatible (32 kilobytes), real addresses 8000-FFFF
4 pre-wired input device selectors (active low), port addresses 00h-03h
4 pre-wired output device selectors (active low), port addresses 04h-07h
Display: LCD 16x2
Input: 7-bit keyboard (8-th bit used as latch)
On-board, seb80 has push buttons for manual clock, reset, and NMI generation.
Software is loaded onto the computer via its EPROM. EPROM erasing and programming are done via UV light eraser and an USB-connected general purpose EPROM programmer:
Generating analog NTSC signal (luminance only, no chrominance):
Observing an infinite loop on oscilloscope:
Complete breadboard prototype with debug LEDs on address, data, and control lines: