Re: Steal RAM -- Question

["Bryan Parkoff" <nospam@nospam.com>]

"mdj" <mdj.mdj@gmail.com> wrote in message 
1162876727.181737.225700@h48g2000cwc.googlegroups.com">news:1162876727.181737.225700@h48g2000cwc.googlegroups.com...
>
> Bryan Parkoff wrote:
>
>>     If we are going to build peripheral card using RAM like AE RAMFactor
>> card, we have an ability to force INHIBIT' to be low to disable CASEN',
>> EN80', CD ROM, and EF ROM so they can steal $D000-$FFFF by using RAM card 
>> on
>> periperhal slot rather than motherboard RAM or auxiliary RAM.  Will
>> $0000-$01FF and $0200-$BFFF work to be used in peripheral slot?  I am
>> curious.
>
> I should also point out that the RAMFactor card, just like the Apple II
> memory expansion card it's compatible with does not use INHIBIT', but
> simply has 3 address registers to hold the memory card address, and a
> data register to read/write it. For convenience, the card automatically
> increments the address registers on an access to the data registers.
>
> If you want to play around with it, the hardware addresses are as
> follows:
>
> $C080 - low byte of address
> $C081 - middle byte of address
> $C082 - high byte of address
> $C083 - data byte
>
> (Of course, all addresses are + slot number * 16)
>
> You also need to do a read to the card firmware before it's registers
> are active.

Matt,

    Okay, I understand.  When AE RAMFactor or any memory card is installed 
in slot 1 through 7, SELECT DEVICE is mapped in C08X * 16 and I/O DEVICE is 
mapped in Cx00-CxFF.  If you build new peripheral card, are you limited to 
use 16 I/O switches in C08X * 16 while reading firmware including I/O 
switches from I/O DEVICE ROM.  Correct?
    When AE RAMFactor card is active, data should always be accessed in 
motherboard RAM while it can be transferred from motherboard RAM to 
RAMFactor card.  It is impossible to disable motherboard / auxiliary RAM and 
use RAMFactor card as primary RAM $0000-$FFFF except $C000-$CFFF.  Only 
other RAM card can disable motherboard / auxiliary RAM.

Bryan Parkoff