The NaZ80-A is the first of the build process and is designed as a simple standalone computer with just an LCD display, hex keyboard and basic comms.

What does NaZ80 stand for? Well, 'Not another Z80'. This project has been done a hundred times and there is nothing new about it. However, I've not done it before, so wanted to put one together. This may also include a simple Z80 compiler – yes, not another Z80 compiler. But it's fun writing a high-level language for a processor. It also gives the opportunity to make up some interesting peripherals for this.

I think the idea will be to go from something really simple to something running CP/M, VGA monitor, keyboard, and probably even a floppy drive – I want to keep it retro and not have any Atmels or other processors doing fancy stuff – it's too easy.

Versions:

'A' – Simple computer with LCD display, hex keyboard and a simple monitor program to allow for basic operation.

'B' – Add serial and parallel ports.

'C' – Add composite display and PS/2 keyboard.

'D' – Implement CP/M. 'E' – Add floppy drive.

Why the Z80? Well, like so many (older) people, it holds a special place in my heart. In the '80s, at the age of about 9 or 10, I took on a newspaper delivery job to save up and buy the ZX81. It cost R99 (in South Africa), the same price as in the UK. It was a lot of money for a 10-year-old, but I did it. I can clearly remember going to the shop to buy the computer – so exciting. I remember being on the lounge floor with the ZX81 plugged into our TV, coding away. It was huge fun.

Hardware Specifications

• Z80 Processor
• 4Mhz Crystal Oscillator 
• 256 bytes ROM - Expandable to 32K
• 255 bytes RAM - Expandable to 16K
• 2 x 16 LCD Display
• Hex Keypad

Software Specifications

• Simple Monitor program
• List memory contents
• Edit memory contents
• Run from location
• Built in routines  for LCD, keyboard and other functions

Schematic for the NaZ80-A