83Plus:OS:Nspire Differences

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The TI-84+ keypad for the Nspire runs the TI-84+ software in emulation. The emulation is quite incomplete; the Nspire only emulates the limited subset of the hardware's features that TI's official software actually uses. This page serves mainly as a reference for programmers who want Nspire compatibility.

Missing Features

Z80 Core

The Nspire does not emulate the full Z80 instruction set.

  • Anything involving the index-half registers is broken.
  • Most undocumented Z80 instructions do not work and cause a reset.
  • The emulated 84 has no access to the Nspire file system.
  • IM 1 and IM 2 work.

Flash Limitations

  • Port 14h still functions as it is supposed to; it controls weather writes to protected ports and flash actually take place.
  • Writes to OS space are normally ignored. Normally.
  • The Nspire does not emulate the flash chip's memory-mapped command register system. Instead, an illegal instruction must be issued for writes to flash to take place.
  • 0EDh, 0EEh: The page swapped into memory bank A is erased.
  • 0EDh, 0EFh: The next ldi writes the data to the archive.


  • Sadly, the LCD must be still accessed through port 10h (as opposed to being memory-mapped). No delay is needed for the LCD. In theory, bit 7 of port 10h will always be reset.
  • USB is totally unemulated. Instead, illegal instructions are used to interface with USB. The USB descriptors appear to be screwed up.

Added features

  • The only additional functionality of the Nspire 84 is the illegal instructions. See the Nspire Wiki for more information. Some of these cannot be used from RAM or the Nspire will reboot.
    • A class of 0EDh, 0EDh, xxh, 10h opcodes are used to do some interesting things.
    • 02h: This is used when turning off. Might not work from RAM.
    • 03h: This locks the Nspire so that only the 84 keypad can be used. Reboots the Nspire if run from RAM.
    • 04h: This unlocks the Nspire so that either keypad can be used. Cannot be run from RAM.
    • 05h–2Ch: These are mostly communication related.
    • 2Fh, 30h: These do stuff.
  • The Nspire OS version numbers are even numbered.

Credits and Contributions

  • BrandonW for doing a lot work on discovering the differences.
  • The Hackspire Wiki.