Traditionally, Send and Get work through the legacy I/O port, not through the mini-USB port.
The protocol used by Send / Get is largely understood and partially documented in e.g. the linkguide.
On the computer side, last year, I added partial support for the Send / Get communication protocol through legacy I/O port (not mini-USB) to libticalcs in
https://github.com/debrouxl/tilibs (experimental2 branch). The test_ticalcs_2 TUI front-end makes it possible to send a bunch of commands to e.g. a CBL2, see the input_dbus_ti68k_* files in
https://github.com/debrouxl/tilibs/tree/experimental2/libticalcs/trunk/tests .
I focused on the TI-68k protocol, and on transferring lists, since that's the main input for the CBL2; you need the TI-Z80 protocol and possibly other file types...
The task was quite a bit more complex than I envisioned, and took me a lot of time; I haven't worked that much on new high-profile features since then.
EDIT: oh, and you can always take advantage of the TilEm TI-Z80 emulator, which also uses the tilibs, to communicate with your 84+ calculator using Send / Get. Most other emulators don't provide support for communicating with real calculators. For the same technical reason, the tilibs-based TIEmu TI-68k emulator can do the same thing with real TI-68k calculators.