83Plus:Ports:05

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Synopsis (TI-83 Plus S.E. and TI-84 Plus Family)

Port Number: 05h

Function: RAM Paging Port

This port can be used to control what RAM page is paged into the C000h-FFFFh memory bank. Note that it can only page RAM pages, not flash pages.

Read Values

Returns the current RAM pages.

Write Values

Sets the current RAM page, by giving a value in 00h-07h, inclusive. When you work with the other paging ports, RAM pages are given in 80h-87h, but this port does not need bit 7 to be set. You cannot set the upper four bits.

Synopsis (TI-83 Plus)

Port Number: 05h

Function: Port 16h Configuration Port

This port configures which memory pages are locked or unlocked (i.e. whether or not the PC register is allowed to point within the page) by port 16h. Only bits 0..2 are considered, the rest have no effect.

Read Values

Nothing of value.

Write Values

Writing a set bit to 16h protects the page; writing a clear bit unprotects the page.

Port 05h Bit Port 16h Bit
2 1 0 7 6 5 4 3 2 1 0
0 0 0 ROM 0F ROM 0E ROM 0D ROM 0C ROM 0B ROM 0A ROM 09 ROM 08
0 0 1 ROM 17 ROM 16 ROM 15 ROM 14 ROM 13 ROM 12 ROM 11 ROM 10
0 1 0 X X X X ROM 1B ROM 1A ROM 19 ROM 18
1 1 1 X X RAM 01 X X X X RAM 00

Comments

At least on my TI-84+, if you output a value with bit 3 set, reading from the port will return a value with bit 3 set. This would imply that you can use RAM pages 08h-0Fh, but these RAM pages do not exist--this bit is simply ignored (only bits 0-2 actually determine what RAM page is active.)

Credits and Contributions

  • Michael Vincent: Initial documentation.
  • Tijl Coosemans: Documenting TI-83 Plus functionality here.