Shutter display

docs/pt2-protocol.md

@@ -8,6 +8,7 @@ Focused companion notes:
 
 - [PT2 Copy State Machine](pt2-copy-state-machine.md)
 - [PT2 Menu State Machine](pt2-menu-state-machine.md)
+- [PT2 Shutter Display Trace](pt2-shutter-display-trace.md)
 
 ## Current High-Confidence Facts
 
@@ -579,7 +580,7 @@ RCP-side OTHERS/COPY menu trace:
 - The entry descriptor immediately before `H'6FF0` requires selector `0x0015` in the secondary table: `E400[0x0015] != 0`. Because command 6 writes `E400`, this is probably a CCU-provided feature/visibility bit, and command 6 must be sent in a live continuation/report window to have an effect.
 - When the page sees `F770.2` set, it only follows the local copy-start branch if `F791.7` is already set. That branch sets `F76E.6`, `F795.7`, `F731.7`, `F798=H'C8`, `F711.7`, `F726=H'64`, calls `loc_5500`, then displays `COPY TO SLAVES`. This is the RCP-side equivalent of the serial `0x006D` copy-start effect.
 - If `F770.2` is set while `F791.7` is clear, the ROM diverts through `H'704C` to a `SET RCP` / `MASTER` display path instead of starting copy. That makes `F791.7` a second, likely master/link/session gate for the physical COPY operation.
-- The OTHERS root handler at `H'6EE4` also tests primary selector `E000[0x008F]` (`H'E11E`) bits 11 and 12, and uses them to set `F711.6` and `F711.4`. If those bits are absent, some OTHERS soft keys can appear inactive even when the page exists.
+- The OTHERS root handler at `H'6EE4` also tests primary selector `E000[0x008F]` (`H'E11E`) bits 11 and 12, and uses them to set `F711.6` and `F711.4`. Bench isolation shows this selector is broader than an OTHERS gate: bit 11 makes the SHUTTER seven-segment display show observed `EUS`, probably the manual's `EVS` display, and bit 12 makes it show the literal letters `OFF`; either bit also illuminates the iris AUTO lamp.
 - Candidate gate probes, not final protocol truth:
 
 ```text