Glossary

This glossary defines the TI-specific terms and key RAM symbols used throughout the wiki.

Core concepts

Term	Meaning
bcall	“branch call” — the OS system-call mechanism: `rst 28h` + a 2-byte ID, dispatched through a jump table to a routine on any flash page. See The bcall Mechanism.
bjump	OS-internal cross-page jump: `CALL cross_page_jump` `.dw addr` `.db page` (a tail-jump). The sibling of bcall for the OS’s own use.
RST shortcut	A 1-byte `rst NN` vector that fast-paths a hot routine (`rst 10h`=`_FindSym`, `rst 30h`=`_FPAdd`, `rst 28h`=the bcall dispatcher).
context	The active “mode” (homescreen, Y= editor, graph, an app…). A block of handler vectors at `cxMain` (`0x858D`); the main loop runs the current context’s handlers. See Boot, Contexts & Errors.
paging / banking	The Z80 sees 64 KiB; ports 6/7 swap which 16 KiB flash/RAM page is visible in the two middle slots. See Paging.
APD	Auto Power Down — the standard-timer-driven idle shutoff. See Clock, timers, and power.
RTC	Real-time clock — a 32-bit seconds counter with an epoch of 1 January 1997, exposed through ports `0x40`–`0x48`.
programmable timer	One of three independent source/mode/counter blocks at ports `0x30`–`0x38`; distinct from the two standard interrupt timers.
MathPrint	The 2D “pretty-print” rendering of expressions; on this OS the engine is on page 0x39.

Term	Meaning
BCD	Binary-Coded Decimal — numbers stored as decimal digits (2 per byte), the format of all TI floats.
`TIFloat`	The 9-byte float: 1 type/sign byte, 1 biased exponent, 7 bytes = 14 BCD mantissa digits. See Floating-Point Engine.
`OP1`–`OP6`	The six 11-byte floating-point accumulator registers in RAM at `0x8478`+. `OP1` is the primary accumulator; binary ops use `OP1`+`OP2`, result in `OP1`.
FPS	Floating-Point Stack — a software stack (pointer at `0x9824`) for spilling OP registers during nested evaluation.
guard digits	The 2 extra mantissa bytes past the 9-byte number (`OP1EXT`/`OP2EXT`), used for rounding during math.

Term	Meaning
VAT	Variable Allocation Table — the RAM catalog of every named object, growing down from `symTable` (`0xFE66`). See Variables & the VAT.
object type	The 1-byte type tag of a variable (`RealObj`=0, `ListObj`=1, `ProgObj`=5, `AppVarObj`=0x15…), modeled as the `TIVarType` enum.
archive	Variables relocated to Flash to save RAM; the VAT entry’s page byte then points into Flash. See Variables, archive & unarchive and Flash memory.
Flash page	A 16 KiB ASIC paging unit selected through port `0x06`. It is not necessarily an erase sector; ordinary sectors span four pages. See Flash memory.
Flash sector	The smallest physical region restored to `0xFF` by one sector-erase operation. The one-megabyte top-boot chip uses 64 KiB ordinary sectors and 32/8/8/16 KiB sectors at the top.
garbage collection	Compacting the Flash archive in physical sector units. `archive_gc_collect` at `3C:7733` copies live records, erases reclaimed sectors, and journals its phase in the inactive half of page `3E`. See Variables, archive and unarchive.
RAM heap	The dynamic region from `userMem` (`0x9D95`) up to the VAT; managed by `_InsertMem`/`_DelMem`. See Memory Management.

Symbol	Addr	Meaning
`IY`	(reg)	Held at `flags` (`0x89F0`) almost everywhere, so `(IY+off)` indexes the `SystemFlags` bitfield.
`flags`	0x89F0	The IY-indexed system flag area (`SystemFlags` struct).
`OP1`	0x8478	Primary FP accumulator.
`FPS`	0x9824	Floating-point stack pointer.
`onSP`	0x85BC	SP saved at context/parse start; `_JError` unwinds to it (try/catch).
`symTable`	0xFE66	Top of RAM; the VAT grows down from here.
`kbdScanCode`	0x843F	Last keypad scan code (filled by the ISR, read by `_GetCSC`).
`plotSScreen`	0x9340	The 768-byte graph/display buffer (96×64).
`parsePtr` / `parseEnd`	0x965D / 0x965F	The TI-BASIC parser’s token-stream cursor.

Addresses: written pp:addr where pp is the flash page (00–3F) — e.g. 3D:6745. Page 0 (the always-mapped kernel) is also written ram:addr since Ghidra keeps it in the ram space. A bare 0x…. with no page is a RAM/data address. See Conventions.
bcall IDs vs addresses: a bcall has both an ID (the 2-byte value after rst 28h, e.g. _FlashToRam = 5017h) and a body address (3D:6745). The ID is not an address.
Confidence flags: [confirmed] (seen in disassembly), [standard] (matches documented TI-83+/84+ behavior), [hypothesis] (inferred). See Conventions.
Function names: official TI bcalls are _CamelCase (_FindSym); RE-inferred names are snake_case (findsym_scan).