I've so many tabs open... and so many other bookmarks, this is in no way complete, nor in order. In fact, there are many great ones I've flat-out left out, since this was for tab-cleanup. Maybe I'll get back to this.
ZAC, the z80 compiler, runs /on/ the TI-86. Also comes with an IDE and nice text-editor that also run on the calculator.
This guy is reverse-engineering the 86 right down to gerbers of the PCB. This'd've been /really/ handy, if I hadn't found it so late in the game. Still... Amazing work, and surely useful.
crud, that was supposed to be a link.
TI-85 Port Documentation (The T6A43 CPU is the same, including the ports... mostly.):
There are two files at ticalc.org for the 86's ports... I should dig up their links... those three docs work together to paint a better picture of the T6A43's ports, in general.
... stuff here:
Great Resource, all 'round the site, for z80 stuff, ASM, stuff, TI-OS stuff, and TI-86 programming:
Z80 instruction set:
Z80 ASM stuff:
TI-86 with an STM32?!!!
I dig the hardware-hackery-enthusiasm in this thread... most forumstuff I've found seems mostly limited to writing games, etc...