Vectrex Vector Generator

Archived from groups: rec.games.vectrex (More info?)

As if I don't have enough projects already...

I recently got reinterested in the Vectrex and am working on an idea
which appears to be occasionally suggested, but I don't think ever
implemented: interrupt driven vector drawing routines.

The concept is similar to the Atari Vector Generator used in the
aracade machines: instead of calling the BIOS subroutines (which poll
T1), instead set up a list of opcodes (which can be quite flexible)
which the VVG parses. Instead of polling T1, the IRQ is used and the
VVG becomes an ISR which RTIs back to the game while the vector is
being drawn/moved.

It's been a while since I did any 6809 coding (I cut my ASM teeth on
the CoCo), but it's been coming together fairly quickly. However, I
don't have a Vectrex. And although I think I have a good grasp on how
the VIA and the integrator hardware work, I have some big questions on
timing. (Like how long does it take to charge the Y integrator and
how often should Z and 0ref be recharged?)

I've looked at the BIOS code, but there are some items which I find
puzzling. There seems to be some major cruft, but I might be
completely wrong.

Anyway, any old hands interested in giving me some advice? Anyone
interested in using my VVG? I'll post some source code in the near
future.

A big thanks to all those who came before me and documented how this
unique piece of hardware works.