Rom on $D000-$D7FF

[retrocanada76]

Hi,

 

I noticed the 800 XL stock rom has the $D000-$D7FF range filled with data. What is that ? Wasn't it supposed to be hardware registers ? Or is the Antic on 800XL able to see this ROM and this is in fact the charset ? The bytes in there indeed look like bitmapped data.

 

How does this work ? What if you switch to OSRAM ?

 

Thxs

[phaeron]

It's the self-test ROM. The MMU maps that section of the ROM to $5000-57FF. Note the coincidence between the addresses.

[Rybags]

Switch to "OSRAM" in fact disables the Self-Test regardless of it's setting. Some people (xxl?) have modified their machines to allow the normally inaccessable 2K of Ram to appear at $5000 when PORTB bit 7 and 0 are both 0. That is achieved by use of a custom made MMU replacement and extra modification to allow A15 to be forced low (?)

[xxl]

yes... there is 2K extra ram available also.

 

http://xxl.atari.pl/mapram/

[Mathy]

Hello xxl

 

Could you please translate the text in that link to English? Google does a fairly good job, but it's not quite good enough.

 

Sincerely

 

Mathy

[xxl]

not used bit combination 0x11xxx0 disables the ROM, RAM from $D000-$D7FF enables at the $5000-$57FF.

MapRAM does not affect memory expansion, you can have memory expansion (or standard 64K Atari without memory expansion) and MapRAM together.

[flashjazzcat]

One exception: Ultimate 1MB, which already uses parts of the MapRAM area for the partition table.

[Mathy]

Hello xxl

 

And this doesn't have any negativ side effects?

 

Sincerely

 

Mathy

[xxl]

And this doesn't have any negativ side effects?

 

 

I did not notice any problems

 

 

Ultimate 1MB, which already uses parts of the MapRAM area for the partition table.

 

u1mb modification is not only an memory extension. partition table is not related to mem exp.