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Introduction

Z20X is a simple expandable DIY computing system, built around the eZ80 microprocessor. I chose eZ80 due to its native simplicity and full backward code compatibility with the great and very popular Z80 and Z180. The design goal of Z20X is to offer a good DIY/LIY (Do-It-Yourself/Learn-It-Yourself) kit for system built with through-hole components, simple enough for assembly and learning in deep details, but without the constraints of using only old technology ICs. In order to maintain full exposure to technical details, the system also avoids using secondary MCUs or programmable logic, and sticks only with true hardware solutions.

 

All boards for the Z20X project can be ordered for manufacturing from PCBway.

 

System Summary

eZ80F92 running at 18 MHz        (default on board)

128 KB flash ROM                 (internal for eZ80)

520 KB total RAM on board        (512K external plus 8K internal)

4 MB non-volatile storage        (optional, can be upgraded by changing the IC)

Real-time clock

SSD1963-powered 7.0 inch TFT display with resolution 800 x 480 pixels and touch panel

SD card slot

YM2413 programmable sound generator with amplifier

PS/2 connectors for industry standard keyboard and mouse

Additionally installable processor modules

72-pin expansion header with Z20X bus

Optional expander board with Z20X bus sockets and bonus support for RC2014 bus

 

 

 

eZ80 is a modernised and extended version of Z80. It maintains backward software compatibility with the latter, while adding several new assembler instructions as well as integrated memory and peripheral modules. It is not a closed system microcontroller though, but a true microprocessor with proper address and data buses, as well as all other control signals as known from the Z80. The eZ80 also supports full 16 megabytes of linear address space. Runs at up to 20 MHz, and can be up to four times faster than a conventional Z80. It is also quite clean and easy to learn system, ideal for initial start with computing technology, and a great way to spend some time for hobby.

Full information about eZ80 can be found on the ZiLOG’s website, but the most important file there is its Datasheet.

The Z20X computer is built around eZ80F92, but it can also use eZ80F93, which is a variant with less internal memory, but otherwise a full equivalent to the ‘F92 and within the same IC package.