83Plus:Ports:28

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Synopsis

Port Number: 28h

Function: Block Memory Mapping 8000h

By an order of 64 bytes per block, this port can re-map data from ram page 1 to reflect the memory in 8000h - BFFFh no mattter contents of port 7. This port does not map the entire page but only 64 bytes times the value in this port. It maps it starting from low memory (8000h) to high(BFFFh).

Read Values

• This port reads the last value written to it.

Write Values

• [00h - FFh]: The value times 64 equals the number of bytes that get re-mapped starting from 8000h. So a vaule of 18h would re-map data in 8000h - 85FFh.

Comments

I can image this port having slighly more purpose than port 27, however it is still unusual.

Also I have left this Stubbed (like to 27) because more info is needed on this port, I haven't fully investigated it, but theres seems to be enough for generally use. Wikification is also needed because I believe the name and the description could be confusing.

Credits and Contributions

• James Montelongo