Former prototypes

First Protoype


April 2021: The first prototype of Zeal 8-bit computer came to life, it has a small form factor, 10x10 cm, and it is also simple yet enough to have a running computer. Here are its key features:

  • Z80 CPU
  • 32KB of accessible ROM
  • 128KB of RAM, accessible via banking
  • 5 LEDs
  • Reset switch
  • Micro USB power input
  • Address, data and CPU signal lines available on 2.54mm pins
  • Active 10MHZ oscillator (SMD)

The process of making it, from choosing the parts to design is explained in Part I The beginning

Second prototype


June 2021: The second prototype was finalized, the PCB is much bigger than the former one, 20x11cm, but it embeds more features. This one can be considered as a standalone 8-bit board thanks to its I/Os and its keyboard PS/2 port.

  • Z80 CPU
  • Z80 PIO for I/Os
  • 256KB of ROM, accessible via banking
  • 512KB of RAM, accessible via banking
  • 8KB FRAM spot (unused)
  • PS/2 Keyboard connector with logic decoding
  • All board logic done with gates (74HCxx chips)
  • 5V to 3.3V converters
  • Video extension port with 3.3V address/data/signals lines
  • Extension port with 5V signals
  • User port, giving access to PIO's port B
  • Debug port with all the CPU signals
  • Active 10MHZ oscillator (SMD)
  • (Big) 1A fuse
  • Power and reset switch

Third prototype


December 2021: The third prototype of Zeal 8-bit computer, it's a hybrid form factor in terms of size, this one is 15x10cm. It was possible to make it smaller thanks to the two PLDs (Programmable Logic Device) which are in charge of doing the decoding logic but also thanks to the smaller fuse. Thus, we can save a non-negligible amount of 74HC chips. This prototype also officially adds an I2C and a UART which have new their own external port. Thanks to this, we also have a 32KB I2C EEPROM embedded. Its main purpose will be to save preferences.

  • Z80 CPU
  • Z80 PIO
  • 256KB of ROM, accessible via banking
  • 512KB of RAM, accessible via banking
  • 2 PLDs for logic decoding
  • PS/2 keyboard port with its logic
  • Onboard (software) I2C and UART bus
  • Extension port with 5V signals
  • System and user ports for internal buses (I2C/UART) and PIO port B
  • Debug port with all the CPU signals
  • 40-pin video card connector
  • 10MHz DIP oscillator
  • Smaller fuse w/ socket

Fourth prototype


February 2022: Fourth and pre-final prototype for Zeal 8-bit computer, the board keeps its size of 15x10cm but presents more features thanks to the gain of space made with the use of PLCC packages. Three components are now in PLCC package: the processor, the PIO and the Flash (used as a ROM). They are all presented inside a socket, making it possible to replace them without soldering.

In terms of features, the main change concerns the physical memory. Indeed, the banking system has been changed for an MMU. The main difference relies on the fact that the virtual memory is now much more versatile: ROM, RAM, VRAM can be mapped anywhere inside the Z80's 64KB memory. The MMU makes the board compatible with almost any existing operating system written for the Z80.

Here is the full list of features:

  • Z80 CPU in PLCC package (w/ socket)
  • Z80 PIO in PLCC package (w/ socket)
  • MMU offering a 22-bit (4MB) physical address space, and 4x 16KB virtual address space
  • 256KB of flash. The flash is in PLCC package (w/ socket)
  • 512KB of RAM
  • PS/2 Keyboard connector
  • I2C RTC w/ 2032 battery socket
  • Fuse w/ socket
  • 10MHz DIP oscillator
  • USB-C for power input
  • 40-pin extension port
  • 16-pin user port for accessing internal buses (UART - I2C) and PIO port A
  • 40-in video card connector