A vintage Z80 CPU forms the core of the system. However, it uses a modern ATMEGA328P microcontroller (running the Arduino boot loader and my own custom Z80/ATMEGA interface routines) to provide most of the I/O capability.
An additional ATMEGA328P is used to provide a composite video output (using Grant Searle’s design) which drives a video converter so that a VGA monitor can be used.
The Z80 runs a custom BIOS which fits into a very small portion of the 8K EEPROM. The remainder of the memory map is occupied by 56KB of RAM.
Various I/O calls have been implemented including writing to the video interface and reading characters from a serial terminal. I’m still deciding how I’ll interface the system to a keyboard.
The Z80 BIOS provides access to the SD card reader via the ATMEGA microcontroller.
NASCOM 8K BASIC can be loaded from the SD card but my preference is the superior Z80 version of BBC BASIC, which was created using a series of source files kindly provided by the author.
Just connect your PS2 keyboard to it and then you get serial and parallel outputs related to the keys that you press. I'd thought about building my own interface, which would be pretty simple to do, but this seems like it will do the job.
Less than £3 delivered. Ordered.
I'll connect it to my Arduino Uno first to see what it sends out.
I bought one of those nice cheap Bluetooth keyboards and was planning on using it with an HC-05 Bluetooth module. However, although the keyboard works fine with other things, the HC-05 does not work with keyboards, regardless of what the seller claimed.