In the previous post I mentioned at the end that the BIOS, running on the ATMega328p, was only capable of communication one way. There are a couple of mailbox memory locations that are used to pass keystrokes to the 8-bit CPUs (Z80 or 6502), yet no way of receiving data back, other than an acknowledgement that the keystroke has been processed. In order to make the BIOS a bit more BASIC-friendly, I needed to add …
First, an introduction. Near the end of July Bernado Kastrup (aka The Byte Attic) put a shout-out on Twitter: A few of my followers suggested I was that man, given my previous experience porting R.T.Russell’s excellent BBC Basic for Z80 to my BSX homebrew and the Spectrum Next. Although the prospect of a shiny new toy to play with was tempting, my projects are backing up, and I would probably not get started on this …
I decided quite early on in this project that I’d try to use interesting and contemporary technology to build the BSX, and make the BSX as simple to build on a breadboard as possible. The GAL is a perfect fit for all those criteria; it’s a technology I’ve not used before, it will cut the logic chip count down somewhat, and is a component that’s been around since the 1970s. What is a GAL A …
