Only 2 banks available
switch is implemented by high/low of VIA ORB PB6
switching is usually done by setting the corresponding DDR register to input (PB6 goes high automatically) or output (PB6 goes low automatically)
vectrex default state is PB6 = INPUT
PB6 high enables BANK 1
PB6 low enables BANK 0
therefor the default vectrex bank upon startup is BANK 1!
Here John Dondzilas original rec.games.vectrex post (29.10.1999):
EXTRA ! EXTRA ! READ ALL ABOUT IT - PCJOHN AND ANOTHER VECTREX FIRST !!!
Thanks to Peter Pachla's suggestion, I spent the last 2 nights working on
the software selectable mini bankswitch cart and I'm pleased to announce:
SUCCESS !!!
Hardware wise is really easy, just wire the PB6 line (pin 35) to the
high address line (A15) on the 64K EPROM.
The software end was a little trickier, the 6522 info I have and the actual
execution of the thing don't work quite the same ...
Basically, if you set the PB6 line to INPUT, it seems to automatically go
high. If you set it to OUTPUT, it goes low. You can send a high bit in the
output mode, but it will only pulse once, then reset to low. This could be
useful for larger carts, but I need the 2 banks to stay steady right now without
re-writing all 8 programs. I'm not sure if my manual is wrong or the Vec does
this, either way - it works. Now I just need to test it on some more machines
before I implement it into the final package.
Looks like emulator users will be getting Volume I and Volume II
seperate binaries.
JD
Emulator:
if a bin file is 32k < Size <= 64K, Vide assumes this bankswitch scheme