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08 — Display & LCD

Deep dives: Graphing (graph buffer → LCD, transforms) · Table & Y= Variables (text grid).

The TI-84+ shows a 96×64 monochrome image — the OS only ever drives a 96×64 region (_ClrLCDFull clears all 768 bytes of it: 8 row-passes × 12 columns × 8 data bytes). The underlying controller (Toshiba T6K04 / later Novatek) has wider video RAM (up to 128 px), so 96×64 is the visible area, not the controller’s geometry. It is reached through I/O ports 0x10 (command) and 0x11 (data). The OS keeps a graph/screen buffer in RAM and renders text via a built-in font.

Controller [confirmed against code]

  • port_lcdCmd (0x10): commands — set row, set column, set Y, on/off, contrast.
  • port_lcdData (0x11): read/write a byte of pixels at the current address.
  • The panel is organized in 8-pixel-tall rows; _ClrLCDFull (01:60E4) loads A=0xB8, subtracts 8 each pass and stops at 0x80 → row commands 0xB8 … 0x80 (8 rows of 8 px = 64 px tall), calling _ClearRow per row with interrupts masked (DI). [confirmed]
  • Command bytes (all grounded in _ClrLCDFull/_ClearRow/lcd_set_col_cmd):
    • Row (page) select = 0xB8 − 8·row for row = 0…7 (i.e. 0xB8, 0xB0, … 0x80), sent to 0x10 via lcd_set_col_cmd (01:5A89), which only emits the byte when 0x80 ≤ A < 0xC0 (guards the row/Z-address range). _ClrLCDFull walks this by loading A=0xB8, calling _ClearRow, then SUB 0x8 and looping while A ≥ 0x80 (B=0x80).
    • Column select = 0x20 + col, sent raw to 0x10. _ClearRow (01:6934) walks E from 0x20 to 0x2B (CP 0x2C terminates) = 12 columns (12 bytes × 8 px = 96 px wide), writing 8 data bytes to 0x11 per column — the B=0x08 inner djnz loop writes one byte per pixel row (8 rows). [confirmed]
    • Contrast: lcd_set_contrast (01:5A59) writes the contrast level to the data port 0x11; lcd_get_contrast (01:5A60) reads it back from the controller with IN A,(0x11) (the standard dummy+real LCD read), not a command re-send. The level is also held in RAM at contrast (0x8447); the command-port form (contrast+0x18)|0xC0 is what _LCD_DRIVERON (page 06) and the _GetKey contrast keys send to 0x10. [confirmed]
    • Every port access is preceded by CALL ram:0CC3 (lcd_wait), the controller-busy delay. [confirmed]

Text output [confirmed]

  • curRow/curCol (0x844B/844C) — the homescreen text cursor (16 columns wide; _PutC wraps at col 16, calls _NewLine).
  • _PutMap (01:5A98) draws one large-font character at the cursor: it clamps invalid codes to 0xD0, computes an initial char * 8 offset, then bjumps to the page-7 large-font blitter, which adjusts that offset to the actual 7-byte-stride glyph table before copying an 8-byte render record. [confirmed]
  • _PutC (01:5B4C) = _PutMap + advance cursor + newline handling; _PutS prints a string; _NewLine scrolls.
  • _DispHL (01:5BF6) prints HL as a right-justified 5-digit decimal: repeated _DivHLBy10, digits +0x30, leading zeros → spaces, writing the digits backward from 0x847C into the OP1 scratch area, then _PutC/_PutMap each digit. [confirmed]

Screen buffers [standard]

  • plotSScreen (0x9340, 768 bytes = 96×64/8) — the main graph/back buffer.
  • saveSScreen (0x86EC, 768 bytes) — saved copy (e.g. for menus over the graph).
  • _GrBufCpy (04:60A3) blits plotSScreen to the LCD; _GrBufClr (04:6071) zero-fills the 768-byte graph buffer (LD HL,0x9340; LD (HL),0; LDIR) and does not touch the LCD.

Fonts [confirmed]

  • Large font: glyph table is on page 7, base 07:45FF, with a 7-byte stride per glyph (not 8). _PutMap (01:5A98) clamps the code (0 or ≥0xF8 → 0xD0), computes HL = char*8 (three ADD HL,HL), then bjumps via trampoline ram:3B3D to the blitter put_glyph_large (07:4588). The blitter does HL = 07:45FF + char*8, then lgfont_glyph_ptr_adjust (07:45EB) subtracts char (it shifts char*8 right by 3 → char, then SBC HL,DE), yielding the real glyph pointer 07:45FF + char*7. It then copies an 8-byte record via _Mov8B (ram:1A94, 8× LDI) into RAM at 0x845A (lFont_record), which the renderer blits. [confirmed] (The stride is 7 bytes while the copy is 8 bytes — the 8th byte overlaps the next glyph’s first row — so the table packs glyphs at 07:45FF + char*7.)
  • Alternate large fonts: two bits in (IY+0x35) select a replacement glyph source before the page-7 table read — bit 5 loads A=0x01 and calls ram:36E7 (bjump to 3B:7BFB), bit 1 loads A=0x76 and calls ram:3E1F (bjump to 3B:7B9C); both are font-hook routines on page 3B that take the A value as a selector. When neither bit is set, the page-7 table at 07:45FF is used. [confirmed]
  • Small/variable-width font: _VPutMap/_VPutS (graph screen, pixel-addressed via penCol/penRow).

Indicators

  • flags.indicFlags bit 0 = the run/busy indicator (the moving dashes top-right); _ClrLCDFull preserves it across a clear; _RunIndicOn / _RunIndicOff toggle it. [confirmed]

LCD command bytes and glyph table

  • LCD command bytes confirmed by tracing _ClrLCDFull (01:60E4), _ClearRow (01:6934) and lcd_set_col_cmd (01:5A89): row (page) select = 0xB8 − 8·row (range 0xB8 … 0x80, stepping down by 8), column select = 0x20 + col (range 0x20 … 0x2B, 12 columns = 96 px), command port 0x10 / data port 0x11, busy-wait via ram:0CC3. Contrast is held at RAM contrast (0x8447) and written to the data port 0x11 by lcd_set_contrast (01:5A59). See Controller. [confirmed]
  • Large-font glyph table pinned: page 0x07, base 07:45FF, 7-byte stride (put_glyph_large @ 07:4588 → glyph ptr 07:45FF + char*7 via 07:45EB, then _Mov8B copies an 8-byte record to RAM 0x845A). See Fonts and Flash Page Map. [confirmed]