Wednesday, 27 February 2019

Vic20 Programmer's Reference Guide

Having become more and more interested in the computers that started it all for me, I've been poking (geddit?) around in my attic among my collection of 8-bit computers, running emulators and buying hardware (leads and adaptors) and starting to use some of these machines again.

I have quite a collection - there was a time when you could easily find them at car boot sales for a fiver,  and I think that one of the Vic20s I have is the one I was given as a teenager.

I've always thought that I'd return to these computers, maybe in retirement, but it's happened a bit sooner.
There's something very exciting about these early home 8-bit machines. You're presented with a flashing cursor and in order to do anything, you need to type a command or two in basic (LOAD and RUN if you wanted to play a game). I believe this fact is why so many of my generation became so interested in software development, and it's something that was lost when a/ many turned to consoles because they only wanted to play games and b/ computers gained more graphic interfaces, separating the user from the workings.

Back to the point. I've begun writing a game for C64. I couldn't help myself. After much searching of the attic, I couldn't find a copy of the C64 Programmer's Reference Guide. I easily found it as a scanned pdf online, which is fine, but it's harder to use that than simply flicking through the pages of a book. (I will buy a copy, they come up on eBay. No doubt I will then find a copy I already owned.)

One of the things I really wanted was a reference guide for the instruction set. Although the C64 has a 6510 processor and the Vic20 a 6502, the two processors are identical but for a small difference. And I did find a Vic20 Prog Ref Guide, and the instruction set reference is identical.
It'll be handy when I make the Vic20 version of my new game.

It's very well-thumbed - I was as obsessed with programming as I am now. This is clearly my own original copy. It has some lined A4 with notes in my handwriting. It feels weird handling the book, a little bit like I've gone back 38 years in time, grabbed the book and brought it back with me.
(This page has my own instructions for using the monitor programme that I wrote in machine code, as a tool for writing more machine code. I used to write my programmes on paper and assemble them by hand before typing in the hex. I'm sure the monitor is on a tape somewhere in the attic.)

End note:
As part of my foray into this new-old world, I've discovered that there are some amazing people producing hardware and games (on cartridge/disc/tape) for these old computers. To support and encourage that, I've begun this project.

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