forked from arti/vt1200
SDD
3fd1e13b2e
Distils public docs into reference/keyboard-mouse/PROTOCOL.md for the level-1 Keyboard (27) / Mouse (26) device tests: - keyboard: 4800 8N1 RS-423, self-test via FD -> 01 00 00 00 (errors 3D/3E) - mouse: 4800 8O1 RS-232, self-test via 'T' -> 4-byte report (errors 3D/3E, >=0x20 fatal) - separate ports: DUART2 A=keyboard, B=mouse (NOT daisy-chained) MAME already has an LK201 device (src/mame/dec/lk201.cpp/.h) but no DEC mouse.
95 lines
3.5 KiB
Markdown
95 lines
3.5 KiB
Markdown
# Hardware
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A separate inline box: a 4P4C socket for the LK401's own cable, and USB out to the host.
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> **Provisional.** The interface below assumes the keyboard's output idles near 0 V and swings
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> towards +12 V (RS-232 polarity, no negative rail). [Phase 1](../docs/phase1-bench.md)
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> measures this; revise the circuit before building if the measurements disagree.
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## Block diagram
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```
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USB 5V ──┬──────────────────────────────── Arduino Micro (5V)
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│
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polyfuse 500 mA
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│
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12 V boost ──┬── 470 µF ── GND
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│
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4P4C pin 3 (+12 V) ◀──────┘
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4P4C pin 2 (GND) ◀────────────────────────────── GND
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4P4C pin 4 (kbd TX) ──▶ [RX inverter] ──▶ D0 / RX1
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4P4C pin 1 (kbd RX) ◀── [TX inverter] ◀── D1 / TX1
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```
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The pin numbers are `lkkbd.c`'s; replace them with the Phase 1 results.
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## Receive path (keyboard → Arduino)
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An NPN inverter. It also protects the 5 V input from the keyboard's 12 V swing.
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```
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kbd TX ──[10k]──┬── B 2N3904
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│
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[10k] 5V
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│ │
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GND [4k7]
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│
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├──▶ D0 (RX1)
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C
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E ── GND
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```
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Keyboard idle (≈0 V) → transistor off → D0 pulled high → UART idle. Correct.
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## Transmit path (Arduino → keyboard)
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Also an NPN inverter, with its collector pulled up to 12 V so the keyboard sees a full-swing
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signal.
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```
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D1 (TX1) ──[10k]── B 2N3904 12V
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│
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[4k7]
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│
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├──▶ kbd RX
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C
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E ── GND
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```
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UART idle (5 V) → transistor on → keyboard input ≈0 V (mark). Correct.
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If an RS-232 transceiver (MAX232/MAX3232) or a 74HC14 turns up in the parts bin, it can replace
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both inverters. The transistor version needs nothing unusual.
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## Power budget
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USB 2.0 supplies 500 mA at 5 V. With a boost module about 80 % efficient, each 1 mA the keyboard
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draws at 12 V costs about 3 mA at 5 V, and the Micro needs about 40 mA. The keyboard's current is
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measured in Phase 1; if its LED-flash peak goes over about 150 mA, we'll need a bigger bulk
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capacitor or a USB 3 / powered port.
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## Bill of materials
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| Qty | Part | Notes |
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|-----|------|-------|
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| 1 | Arduino Micro (A000053) | Teensy 2.0 is a drop-in alternative |
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| 1 | 5 V → 12 V boost module | on hand; set to 12.0 V before connecting |
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| 1 | 4P4C (RJ9/RJ10) PCB socket or breakout | takes the LK401's cable |
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| 2 | 2N3904 (or BC547) NPN transistor | |
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| 3 | 10 kΩ resistor | |
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| 2 | 4.7 kΩ resistor | |
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| 1 | 470 µF 25 V electrolytic | 12 V rail bulk capacitor |
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| 1 | 100 nF ceramic | 12 V rail, at the socket |
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| 1 | 500 mA polyfuse | on USB 5 V into the boost |
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| 1 | Enclosure | about 80 × 50 × 25 mm |
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| — | 24 MHz 8-channel USB logic analyser | test equipment, optional; use with PulseView |
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## Arduino Micro pins
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| Pin | Use |
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|-----|-----|
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| D0 (RX1) | From the keyboard, through the receive inverter |
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| D1 (TX1) | To the keyboard, through the transmit inverter |
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| D13 (LED) | Blinks on each byte received |
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| USB | HID keyboard and debug console |
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