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Glossary

Quick definitions for the terms and key RAM symbols used throughout this wiki.

Core concepts

TermMeaning
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.
bjumpOS-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 shortcutA 1-byte rst NN vector that fast-paths a hot routine (rst 10h=_FindSym, rst 30h=_FPAdd, rst 28h=the bcall dispatcher).
contextThe 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 / bankingThe Z80 sees 64 KiB; ports 6/7 swap which 16 KiB flash/RAM page is visible in the two middle slots. See Paging.
APDAuto Power Down — the timer-driven idle shutoff.
MathPrintThe 2D “pretty-print” rendering of expressions; on this OS the engine is on page 0x39.

Floating point

TermMeaning
BCDBinary-Coded Decimal — numbers stored as decimal digits (2 per byte), the format of all TI floats.
TIFloatThe 9-byte float: 1 type/sign byte, 1 biased exponent, 7 bytes = 14 BCD mantissa digits. See Floating-Point Engine.
OP1–OP6The six 11-byte floating-point accumulator registers in RAM at 0x8478+. OP1 is the primary accumulator; binary ops use OP1+OP2, result in OP1.
FPSFloating-Point Stack — a software stack (pointer at 0x9824) for spilling OP registers during nested evaluation.
guard digitsThe 2 extra mantissa bytes past the 9-byte number (OP1EXT/OP2EXT), used for rounding during math.

Variables & memory

TermMeaning
VATVariable Allocation Table — the RAM catalog of every named object, growing down from symTable (0xFE66). See Variables & the VAT.
object typeThe 1-byte type tag of a variable (RealObj=0, ListObj=1, ProgObj=5, AppVarObj=0x15…), modeled as the TIVarType enum.
archiveVariables relocated to flash to save RAM; the VAT entry’s page byte then points into flash. See Variables, Archive & Unarchive.
garbage collectionCompacting the archive flash when it fills (“Garbage Collecting…”). The GC-core candidate flash_gc_relocate@3C:7BD0 is a project-local inferred label, not a defined function in the current live DB nor a WikiTI or ti83plus.inc equate.
RAM heapThe dynamic region from userMem (0x9D95) up to the VAT; managed by _InsertMem/_DelMem. See Memory Management.

Registers & RAM symbols

SymbolAddrMeaning
IY(reg)Held at flags (0x89F0) almost everywhere, so (IY+off) indexes the SystemFlags bitfield.
flags0x89F0The IY-indexed system flag area (SystemFlags struct).
OP10x8478Primary FP accumulator.
FPS0x9824Floating-point stack pointer.
onSP0x85BCSP saved at context/parse start; _JError unwinds to it (try/catch).
symTable0xFE66Top of RAM; the VAT grows down from here.
kbdScanCode0x843FLast keypad scan code (filled by the ISR, read by _GetCSC).
plotSScreen0x9340The 768-byte graph/display buffer (96×64).
parsePtr / parseEnd0x965D / 0x965FThe TI-BASIC parser’s token-stream cursor.

Conventions

  • 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).