VRIO/PlasmaNew/FIRMWARE.md

PD01D221 firmware analysis (tms27pc512.BIN)

Reverse-engineering notes for the dumped controller firmware — the 64 KB TI TMS27PC512 EPROM (U3) from the Babcock PD01D221. This is the authoritative source for the display's command set, and it feeds both vPLASMA and the planned hardware replica.

Dump: tms27pc512.BIN, 65,536 bytes, MD5 b775427806857f60ca4a4cc501f4b5cc. Analysis tooling: hc11dis.py (a purpose-built 68HC11 disassembler — the toolchain has no m68hc11 target).

Memory map

• CPU $8000–$FFFF = EPROM upper 32 KB, 1:1 (the HC11 vector table lands at ROM offset $FFC0–$FFFF and is valid, which pins the mapping). The EPROM's lower 32 KB is unused (all $00) — only A15-high is decoded to the ROM.
• Code: $9000–$B8xx. Data/tables: $8000–$8FFF (demo), $98AC+ (dispatch tables), $BC03+ (font descriptors), $C000–$DFFF (glyph bitmaps + graphics).
• RAM (Mosel MS62256, 32 KB) at low addresses: HC11 registers on page 0 ($00–$3F; SCSR=$2E, SCDR=$2F), zero-page variables $40–$FF, RX ring buffer at $0228, and ten 128×32 screen buffers from $0F6D up.

Vectors

Vector	Target	Notes
RESET	$9059	Init: registers, stack $0227, then main loop
SCI (serial rx)	$B85C	Interrupt-driven receive → ring buffer
COP watchdog	$905E	(re-inits)
others	$9059	default → reset

Architecture

1. SCI RX ISR ($B85C) — on RDRF, reads SCSR/SCDR, stores the byte to a ring buffer at $0228 (write ptr $0228, count $022C). No parsing here.
2. Main-loop parser ($B7E0–$B859) — pulls buffered bytes and runs an ESC-state machine (flag $AF: bit $10 = ESC seen, bit $20 = operand pending). Dispatch is table-driven (below). Printable chars in the current font's [first,last] range ($62/$63) go to the character renderer ($9648), which enqueues a glyph to a deferred rasterizer.
3. Ten double-buffered screens — descriptor table at $A4E0 (10 × 6 bytes): each screen has a draw pointer ($BE) and a display pointer ($BC) into SRAM, 1 KB apart. ESC I sets the draw target, ESC i sets what's scanned to the glass → page-flipping / double-buffering.

Command dispatch

Two jump tables, indexed by byte:

• ESC + letter → command table at $98AC. Valid letters 0x30–0x7E; index = letter − 0x30; null entry = ignored. 58 commands populated.
• Control bytes 0x08–0x14 → table at $994C. index = byte − 0x08.

Most command handlers share a prologue: first sighting of the letter sets the "operand pending" flag and returns; the next byte is the 1-byte operand (in $C6). Multi-operand commands (ESC P/X/Y) collect into a parameter block at $0070.

Control characters ($994C)

Byte	Handler	Meaning
0x08 BS	$99AF	cursor left
0x09 HT	$9966	tab
0x0A LF	$99F3	line feed
0x0B VT	$9A30	vertical tab
0x0D CR	$9A55	carriage return
0x11–0x14 DC1–DC4	$9A5C/$9B34/$9C09/$9CFC	device controls (TBD)
0x0C FF, 0x0E–0x10	—	no handler

ESC commands ($98AC) — confirmed semantics

Cmd	Handler	Meaning
ESC @	$9F26	Clear the active draw buffer (512 bytes = 128×32÷8)
ESC G n	$A42B	Cursor mode, low nibble of $B4 (n = 0–7)
ESC H n	$A44C	Text attributes, low 4 bits of $B1 (intensity/underline/reverse/flash)
ESC K n	$A3EA	Font select (n = 0–9; 8 real fonts)
ESC L	$A556	Home cursor (X=0, Y=0)
ESC Q n	$A51C	Set cursor row Y (range-checked 0–31)
ESC R n	$A539	Set cursor column X (range-checked 0–127)
ESC I n	$A473	Select DRAW page 0–9 (sets $BE from $A4E0 table)
ESC i n	$A4A2	Select DISPLAY page 0–9 (page-flip; sets $BC)
ESC P …	$AAF1	Graphics bitmap write (multi-operand: screen,y,x,w,h,data)
ESC A–ESC F	$9FB6–$A13C	Vector/graphics primitives (line/point/move; pen state $B6, coords $58/$59, line routine $A16C)
ESC X n	$A748	Set graphics pen X (multi-op, 0–127)
ESC Y n	$A644	Set graphics pen Y (multi-op)
ESC J	$A4D4	Toggle mode bit $B7.7 (orientation/display — TBD)

ESC commands — populated but not yet decoded

ESC 0–9 ($9E27+, set continuations — likely custom-char / numeric entry), ESC : ; = , ESC < > W w _ (cluster $AEBA–$AF00), ESC B C D E F variants, ESC M N O ($A5BD/$A5C5/$A5E0), ESC Z ^ z ~ (cluster $AC73–$ACA1), ESC a–f, ESC h l n p q r x. ~30 handlers remain to label — full list with addresses is dumped by the tooling below.

Fonts

Font-pointer table at $BC03 (10 slots) → 12-byte descriptors. 8 real fonts (slots 8–9 are junk pointers, matching the demo's "8 STORED CHARACTER FONTS"):

Font	First–Last	W×H	Notes
0	0x20–0xFF	6×8	base font, full range
1	0x40–0x7F	6×8	uppercase-only
2	0x20–0xFF	6×10
3	0x40–0x7F	6×10
4	0x20–0x7F	12×16	large
5	0x20–0x7F	12×20	largest
6	0x20–0xFF	7×10
7	0x40–0x7F	7×10

Glyph bitmaps live in ROM (~$C000–$DFFF). Exact glyph base + encoding pending — the renderer at $9648 enqueues to a deferred rasterizer; tracing that (or brute-forcing the 'A' pattern at the known stride) will extract the real glyphs to replace vPLASMA's public-domain 5×7 stand-in.

Demo program

Enabled by jumper 6 (PD3) — confirms the JP1 map. A 10-screen scripted demo; the script at $8028+ is literal command usage (pointer table at $8000). It's how the new ESC R/I/Q/i/K commands were first spotted, e.g. 1B 47 00 (ESC G 0) 1B 40 (ESC @) 1B 4C (ESC L) 1B 52 04 (ESC R 4) …

What this means

For vPLASMA (folded in 2026-07-16): the recovered spec replaced the guessed behavior. vPLASMA now uses the 8 real ROM fonts (extracted to src/VPlasma.Core/Device/PlasmaFonts.cs), a pixel-addressed cursor with the real ESC Q (row) / ESC R (column) positioning, ESC K 0–7 font select, and ESC H attributes as the low 4 bits. Verified: 24 unit tests + the three self-test pages render the real glyphs. Still deferred (documented, single-page model retained): the 10 double-buffered pages (ESC I/ESC i) and the vector-graphics primitives (ESC A–F).

For the replica: this is the spec. The firmware confirms a clean model — a byte-stream command parser, a 512-byte-per-page frame buffer, 10 pages with page-flip, 8 fonts, text attributes as 4 flags, plus vector graphics. All of it ports directly onto a modern MCU. The one artifact still to extract is the glyph bitmaps.

Reproduce

python hc11dis.py <hexaddr> <count>      # disassemble from a CPU address
# e.g. python hc11dis.py B7E0 70         # the command parser

Command/control tables are at $98AC / $994C; font table $BC03; screen table $A4E0.