PlasmaNew: replica goes USB-CDC (Win x64 hosts), park pending dump

The cockpit PCs are now Win x64, so the replica needs no real RS-232 — a
native-USB MCU presenting as a USB CDC virtual COM port is transparent to
the host (opens COMx, can't tell it isn't a UART). Records the consequences
(baud cosmetic, timing instant, pin the COM number, LEDs need their own
power) and marks the hardware/protocol thread parked until the U3 EPROM
firmware dump (or Babcock programming manual) is in hand.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

PlasmaNew/README.md

@@ -170,8 +170,37 @@ section or the panel connector while powered.
   the public-domain 5×7 stand-in with the real Babcock glyphs, and
   differential-test against the hardware.
 - **Prototype the replica.** A modern MCU (RP2040 / ESP32 / Teensy) reads the
-  J1 serial bus into the same command parser and drives a 128×32 LED matrix
+  command stream into the same command parser and drives a 128×32 LED matrix
   from the same frame buffer — the per-pixel lit / half-intensity / flash
-  flags in `VPlasmaDevice` map directly onto PWM brightness + blink. Match
-  the J1 pinout, the baud jumpers, and the DTR-ready line so it drops into
-  the original harness. An amber matrix best mimics the neon-orange plasma.
+  flags in `VPlasmaDevice` map directly onto PWM brightness + blink. An amber
+  matrix best mimics the neon-orange plasma; for a true cockpit swap, match
+  the original active area (~12.75" × 3.15", ~0.1" pitch = 128×32).
+
+## Replica interface — USB, not RS-232
+
+The cockpit PCs are now **Win x64**, so the replica likely needs **no real
+serial port**: a native-USB MCU presenting as a **USB CDC virtual COM port**
+is transparent — the host opens `COMx` and can't tell it isn't a UART. This
+deletes the RS-232 transceiver and connector from the BOM. Consequences:
+
+- **Baud is cosmetic** over USB CDC (the 9600/… setting is accepted as a
+  no-op; the two baud-select jumpers need no hardware equivalent).
+- **Timing becomes instant** rather than ~1 ms/byte — harmless for a display,
+  and vPLASMA can still throttle to mimic the original for differential tests.
+- **Pin the COM number** the host expects (original was COM2) in Device
+  Manager so it drops in with no host-side config change.
+- **DTR/RTS still cross** the CDC link if any host logic ever needs them (the
+  game didn't use flow control).
+- **Power gotcha:** USB alone can't drive the LED array at full brightness —
+  use USB for data + a **separate DC feed** for the LEDs (or USB-C PD).
+
+Transparency assumes the host reaches the display as a Windows `COMx`
+endpoint — e.g. DOSBox-X `serial2=directserial realport:COMx`, which a USB
+CDC port satisfies perfectly. Confirm the current drive path.
+
+## Status
+
+**Parked pending a firmware dump.** The software emulator (vPLASMA) is built
+and released; this hardware/protocol thread is blocked on getting the U3
+EPROM image (or the Babcock programming manual). Resume at the dump plan
+above once a dump is in hand.