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Z80 Single Board Computer


The ZBoard is a complete Z80 microcomputer with an ISA interface for easy programming and debugging in a PC. The ISA interface is built from discrete logic and allows the PC access to the microcomputer's data and address busses, as well as some processor control. This allows the PC to pause the microcomputer, access memory or peripherals, and unpause the microcomputer. I use this feature to program the onboard nonvolatile RAM and to implement a terminal on the host PC. Extensive debugging is also possible as all RAM is viewable.

To give the Z80 more memory (the Z80 can only address 64k), I implemented a paging scheme. The memory is broken into 32k pages with the lower 32k remaining constant and the upper 32k being software selectable. This allows for up to 544k of memory, expandable with eight more wires to over 8M. I used a 128k RAM chip and two 32k FRAM chips. FRAM, or ferroelectric RAM, is a nonvolatile ram that is interchangeable with RAM chips due to its high speed and identical pinout. See for more information on FRAM.

I wrote a basic monitor program / operating system for the board completely in assembly. It interacts with a development environment (which I wrote in C Builder) on the host PC. Together they provided a complete real-time debugging system which also allowed me to verify test programs.

Take a look at the schematic. For more info, including complete program listings and an almost readable schematic, take a look at my project report.


Here are some web resources that I found helpful:


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