Today, Runer112 contacted me with a rumor that the TI-83+ (the original black edition, as opposed to the Silver Edition of the TI-84+/SE) did not perform the type of port mirroring that the community has long assumed and is documented in WikiTI. The evidence came from another community member, Juju, who failed to have the adverse affects on his calculator that writing to port $FF should have caused. This evening, I dug through my dozens of calculators and found one with a physical z80 chip, serial 131424476N-1099A. With a small test program I made using port $41 to read from and write to the keypad (normally port $01), I verified that reads and writes are properly mirrored. I then tried on a newer calculator with the combined bus arbiter/processor ASIC, serial 2265064268S-0402C, and verified that it performed the same way. For reference, its mainboard is labelled 9TA83ASMB-31G.
Therefore, the question remains whether there are some calculators that do indeed display this odd asymmetry in port mirroring that was reported, but not my calculators, or if there's something else at play here. I'll continue testing a few of my other calcs.
Therefore, the question remains whether there are some calculators that do indeed display this odd asymmetry in port mirroring that was reported, but not my calculators, or if there's something else at play here. I'll continue testing a few of my other calcs.