Re: 137179 replacements (again)

Paul Tonizzo wrote:
>
> I'm just curious, why do you need memory on the pcb? I have a schematic for
> a replacement board (I think from Tempest or something) that shows only TTL
> on it.
>
> My apologies in advance if it's a dumb question.

I will try and field this one (no, it's not a dumb question either).

The AVC IC has a push-pull stack onboard so that the vector generator
can JSR and RTS up to a depth of 4(?). So the RAM is required to store
the return address on multiple subroutine jumps.
  The basic idea of the Atari Vector generator is that the vector RAM is
where the main code is written by the game CPU. For all the individual
objects on the screen, the code just JSR's to a section of the vector ROM.
Sort of like sprites, the vector ROM has a big index table in the beginning
so that every object can be referenced by a number, makes the graphics organization nice
and easy.
Received on Tue Jun 8 09:52:43 1999