vt1200/reference/keyboard-mouse/SOURCES.md

Keyboard / mouse protocol — sources

Retrieval date for everything below: 2026-10-16 (all fetched by this session). Originals are preserved in this directory; text/OCR extractions are kept alongside where they were produced. Nothing here is VT1200-specific — see the note at the end.

Primary DEC documents

Source	Local file	What it covers
VCB02 Video Subsystem Technical Manual, EK-104AA-TM-001, DEC Educational Services, Feb 1987 (per vt100.net). Appendix B = LK201 Keyboard Spec, Appendix C = Mouse Spec, Appendix D = Digitizing Tablet.	vcb02-technical-manual-ek-104aa-tm-001.pdf (scanned, 26 MB, no text layer) + vcb02-ek-104aa-tm-001-archive-djvu.txt (archive.org OCR of the same item, useful but noisy)	The authoritative DEC spec for the LK201 keyboard protocol, the VSXXX-AA/-GA mouse, and the VSXXX-AB tablet. URL: https://vt100.net/dec/ek-104aa-tm-001.pdf (mirror of archive.org item 104aatm1).
VCB02 Video Subsystem Technical Manual, AZ-GLGAB-MN, DEC Educational Services, Feb 1986 (the edition Dan McMahill credits with "cleaning out the remaining mysteries").	vcb02-az-glgab-mn-feb86-text.pdf + vcb02-az-glgab-mn-feb86-text.txt (pdftotext -layout)	Same appendices, cleaner OCR. Appendix B (LK201) and Appendix C (Mouse) tables are readable here — this is the copy the facts in PROTOCOL.md are quoted from. URL: https://archive.org/download/bitsavers_decqbusvcbhnicalManualFeb86_19080378/AZ-GLGAB-MN_VCB02_Technical_Manual_Feb86_text.pdf
LK401 Keyboard Product Specification, DEC PS 3032041-0-0, 17 Jan 1990 (rev CX01).	vt100net-lk401.pdf + vt100net-lk401.txt	The keyboard the VT1200 actually ships. States LK401 is "electrically and firmware functionally compatible" with the LK201, frame format (start + 8 data + stop), 4800 baud, self-test 4-byte result, key matrix/divisions. URL: https://vt100.net/mirror/antonio/lk401.pdf
LK201 schematic, MP01395, Oct 1983.	bitsavers-MP01395_LK201_Schematic_Oct83.pdf (scanned, no text layer)	Hardware reference for the keyboard matrix / serial driver. URL: http://bitsavers.trailing-edge.com/pdf/dec/terminal/lk201/MP01395_LK201_Schematic_Oct83.pdf
LK201-AA 8051 firmware, part 23-004M2-00.	bitsavers-23-004M2-00_LK201AA_Firmware.zip (23-004M2-00.BIN, .hex)	Firmware image for the older 8051 LK201. Note: MAME's lk201 device emulates the 6805 LK201 and wants 23-001s9-00.bin, which is not in this zip. URL: http://bitsavers.trailing-edge.com/pdf/dec/terminal/lk201/23-004M2-00_LK201AA_Firmware.zip
VT330/VT340 Programmer Reference Manual, Chapter 15 "Using a Mouse or Tablet".	vt100net-vt3xx-gp-chapter15.html	Corroborates the VSXXX-AA mouse and VSXXX-AB tablet as DEC terminal locator devices on a dedicated "locator port" with the micro-DIN connector. URL: https://vt100.net/docs/vt3xx-gp/chapter15.html

Reverse-engineered / driver sources (usable as documentation)

Source	Local file	What it covers
Dan McMahill, "LK201 Keyboard Interface" (NetBSD docs).	netbsd-lk201-interface.html	The single best public write-up of the LK201 protocol: 4800 8N1, connector pinout, all host→keyboard commands, the 4-byte power-up self-test result and error codes, key modes/divisions, autorepeat. URL: https://www.netbsd.org/docs/Hardware/Machines/DEC/lk201.html
NetBSD, LK201 keycode/division table.	netbsd-lk201-keycodes.html	Complete keycode→key map, grouped by the 14 divisions. URL: https://www.netbsd.org/docs/Hardware/Machines/DEC/lk201_keycodes.html
Paul Flo Williams, vt100.net "LK201 Keyboard".	vt100net-lk201-keyboard.html	A real captured VT320↔LK201 POST exchange (hex), including the FD self-test request and the 01 00 00 00 reply, and the stuck-key variant 01 00 3D AE. URL: https://vt100.net/keyboard.html
Linux drivers/input/keyboard/lkkbd.c.	linux-lkkbd.c	Working LK201/LK401 driver. Command bytes (FD AB D3 E9, modes, LEDs, bell/keyclick), error codes 3D/3E, and the AB ID reply distinguishing LK201 (byte=1) from LK401 (byte=2). URL: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/drivers/input/keyboard/lkkbd.c
Linux drivers/input/mouse/vsxxxaa.c.	linux-vsxxxaa.c	Working VSXXX-AA/-GA/AB driver: 4800 8o1, 'T' self-test trigger, POR/REL/ABS packet layouts, error-code semantics. URL: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/drivers/input/mouse/vsxxxaa.c
elkay (issinoho), a modern LK401→USB adapter.	elkay/ (git clone, shallow)	docs/protocol.md and firmware/include/lk.h — a clean, implementation-grade restatement of the LK201/LK401 protocol including the E9 LK401-mode command. URL: https://github.com/issinoho/elkay
lk201emu (pkoning2), LK201 emulator firmware.	lk201emu/ (git clone, shallow)	Arduino firmware that impersonates an LK201: shows exactly what to reply to FD (01 00 00 00) and AB. URL: https://github.com/pkoning2/lk201emu
vtbt (tsowell), Bluetooth→LK201 bridge.	vtbt/ (git clone, shallow)	Another independent LK201 host implementation (ESP32), useful for cross-checking timing/sequence. URL: https://github.com/tsowell/vtbt
libgii man page "LK201/LK401 keyboard input".	libgii-input-lk201.7.html	States LK201 and LK401 share the connector and serial format. URL: https://www.ibiblio.org/ggicore/documentation/libgii/1.0.x/input-lk201.7.html
comp.sys.dec post "The DEC round mouse VSXXX-AA" (Fred Kleinsorge, 1998).	vaxarchive-vsxxx.html	Mouse pinout, 4800 8o1, command set, REL and self-test byte layouts. URL: https://vaxarchive.org/hardware/vsxxx.html
AllPinouts, "Mouse / Digitizer DEC 7-pin".	allpinouts-dec-7pin.html	Connector pinout and the "4800, 8 data bits, odd parity, 1 stop bit" figure for VSXXX-AA/-GA/AB. URL: https://allpinouts.org/pinouts/connectors/input_device/mouse-digitizer-dec-7-pin/

Our own repository (cross-checks)

• ../EK-V1000-SV-002_service-guide.txt — VT1000/VT1200 service guide. Says the terminal uses the LK400 series keyboard (LK401 standard, LK402 word-processing); lists the Keyboard Test (27) and Mouse Test (26) as "firmware requests that the keyboard/mouse do its self-test and display any error code"; shows a separate mouse port with its own loopback connector (12-25628-01).
• ../../docs/EK-V1200-UG-001_installing-VT1200.txt — "The keyboard cable connects to the system box" and "The mouse connects to the system box"; lists a dedicated Pointing Device Connector (Table C-2).
• ../rom-strings.txt — terminal ROM names LK401.C, and carries the messages "The keyboard ROM reported a fault at power-up" and "A key was held down during power-up", matching the LK201/LK401 error codes 3E/3D.

Found but NOT retrieved (visible gaps)

Source	Why	Note
LK400 Keyboard Firmware Requirements	Not located publicly.	The LK401 spec (line 678) points at this document as the definition of the terminal→keyboard command protocol. This is the one document that would make LK401 coverage first-class rather than "inherited from LK201".
VT1200-specific keyboard/mouse protocol	Does not appear to exist.	No VT1000/VT1200/VXT2000 manual documents the wire protocol; the manuals only say "uses the LK400 series keyboard / a 3-button mouse".
MAME keyboard ROM 23-001s9-00.bin (6805 LK201)	Not in the bitsavers zip we have (that zip is the 8051 23-004M2).	Needed if we want to run MAME's lk201 device rather than a HLE model.
bitsavers.org/pdf/dec/terminal/lk201/ directory listing	403 to our fetcher; used the trailing-edge HTTP mirror instead.	Functional equivalent retrieved.
vaxarchive.org/hardware/vsxxx.html over plain HTTP	406 (ModSecurity).	Retrieved over HTTPS with a browser UA.
github.com/.../raw/... for the two Linux drivers	GitHub raw returned a 429 rate-limit stub.	Re-fetched from git.kernel.org instead (identical drivers).