This was another Z80 computer made to learn something new. This one was built using dynamic RAM. All the DRAM control was made using simple logic, no delay lines!

I used a broken Sega SC-3000 case and keyboard.

This one has no CRT interface, but does have a 2x20 character LCD display. I only wrote a DRAM test SW and a driver for the display using assembler. For some reason I seem to have lost all the sources and schematics, maybe this actually only existed on paper. I do have the PAL equations.

Features

•  Z80B running on 6.144MHz
•  32k EPROM 27256
•  64k banked DRAM (4164)
•  8253 timer
•  8255 PPI (keyboard scan lines, ASCII LCD interface)
•  16450 UART

A PLD (PAL 16L8) is used to implement glue logic and replaces several standard logic chips.