Re: How much of a ][ is needed to twitch?

["David Wilson" <mcs6502@gmail.com>]

On Feb 13, 10:30 pm, "mdj" <mdj....@gmail.com> wrote:
> On Feb 13, 8:03 pm, biel...@terra.es wrote:
> > Wasn't it that the slot 3 built-in ROM could be en/dis-abled by a
> > softswitch in the IIe ?
>
> It's also switchable by softswitch, yes, but the default is to enable
> the motherboard ROM, and operating systems prior to ProDOS aren't
> aware of the switch.

They don't need to be. The firmware listing of the enhanced //e ROM
has the following comment describing the code at $C2E2 (called as part
of the RESET handler):

"If there is a ROM card plugged into slot 3, don't switch in the
internal ROM C3 space. If not, only switch them in if there is a RAM
card in the video slot".

Thus internal slot 3 firmware is only active if slot 3 card firmware
is absent and an Aux slot RAM card is present.