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This port only exists as a distinct port on the TI-83 Plus Silver Edition, the TI-84 Plus, and the TI-84 Plus Silver Edition. On the standard TI-83 Plus, it acts as a shadow of port 00.


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 the memory addresses 8000h - BFFFh without regard to the 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.


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

calc84maniac says: This port seems to have no effect whatsoever during memory map mode 1, but I may be wrong about that.

DrDnar says: I concur. It looks like ports 27 and 28 have no effect in memory mapping mode 1.

Credits and Contributions

  • James Montelongo

See Also