Circuit Projects

Electrical/Electronics Blogger

Homemade Z80 Computer

The project creates a Z80 computer which provides the possibility of producing a video board that utilizes TV as the monitor.

There are two boards, CPU and video, that comprise the machine and a keyboard, which are connected to each other through ribbon cables. The system ROM and character generator was burnt into two 27C256 UV EPROMs. The Z80 also features ZiLOG Z80 CPU running at 4 MHz, built-in monitor program, 32kBytes of RAM, full stroke keyboard, and 1 kBytes of video RAM.

The Z80 refresh function is gated but it will not have any effect since this is a classical computer circuit. The video panel provides the clock and interrupt signals for the CPU. When the CPU gives address at the bottom 4k of the full 64k address space, the EPROM with system software circuit is selected. A SPI interface for SD card may be used instead of creating a simple IDE interface since a hard drive is too heavy and large on this board. the short-circuit protectors of the keyboard are a series of 1N4148 diodes.

Simple graphics can be drawn by using the 16 different quarterpoint characters stored in the character generator.

Click here to see the rest of the project.

Tags: homemade, diy, Z80, computer,

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