8192 bytes RAM, 2400 bytes user accessible
64 kB ROM
Known ROM versions (known, dumped, unconfirmed, unreleased):
1.0
1.1
1.1K
1.5K
1.6K
1.8K
V2.00
V2.0V
The TI-81 is Texas Instruments' first graphing calculator, released in 1990. It is based on a 2 MHz Toshiba Z80 clone, with a 8 kilobyte RAM chip providing 2400 bytes of user memory. The relatively small 64 kilobyte ROM chip makes the TI-81 about as responsive as the TI-82 that followed it.
The display is a 64x96 dot-matrix TN LCD on all models without the 'B' hardware revision, and a 64x96 STN LCD on 'B' revisions. The display is memory-mapped on ROM 1.xx and port-mapped on ROM V2.0x.
To date, eight ROM versions have been found, and five have been dumped. Due to the lack of a link port, dumping a TI-81's ROM is not a simple task: instead, an assembly program is loaded through a complicated task and the ROM contents are displayed on the screen. An OCR program reads what the screen displays, and after some tinkering a ROM file is produced. Theoretically, it is possible to put a link port in a V2.0x TI-81 and dump the ROM via link port; this has not been done due to the effort required to dump already documented ROMs.
Unlike later calculators, the TI-81 has noticeable differences between ROM versions, albeit small. Version 1.8K is designed to work with a different display, and has 40 contrast steps instead of 10 to support the higher contrast ratio of the display. V2.00 returns to the old display type and 10 contrast steps, and behaves to the user much like the original TI-81. However, it is internally different, based on TI-82 hardware; display access is slower, resulting in a noticeably slower (but by all means usable) scrolling speed compared to earlier TI-81s.