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docs/pt2-iris-mblack-link-rom-trace.md

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+# PT2 IRIS/M.BLACK LINK ROM Trace
+
+This note records the ROM evidence for the bench-visible
+`IRIS/M.BLACK LINK` lamp.
+
+## Confirmed Host Trigger
+
+The isolated bench trigger is:
+
+```text
+00 00 13 40 00 09  ; command 0, selector 0x0013, value 0x4000
+```
+
+Command 0 mirrors nonzero selector writes into both `E000[selector]` and
+`E800[selector]`, then queues the selector for internal processing. For this
+frame that means:
+
+```text
+E000[0x0013] = 0x4000
+E800[0x0013] = 0x4000
+```
+
+The current-table word is `E800 + 2 * 0x0013 = H'E826`.
+
+## Selector Handler
+
+The selector dispatch table maps selector `0x0013` to `H'2E06`.
+
+Focused linear decode:
+
+```text
+H'2E06  BTST.W #15, @H'E826
+        set/clear F791.6 and F713.4
+
+H'2E1E  BTST.W #14, @H'E826
+        set/clear F791.5 and F716.7
+```
+
+Bench labels:
+
+| Selector value | ROM latch bits | Visible result |
+| --- | --- | --- |
+| `0x8000` | `F791.6`, `F713.4` | far-right `SLAVE` lamp |
+| `0x4000` | `F791.5`, `F716.7` | `IRIS/M.BLACK LINK` lamp |
+| `0x0000` | clears both bit groups through `H'2E06` | both latch groups clear |
+
+## Other Trigger Path
+
+There is also a local panel-input path:
+
+```text
+F006.7 / F6DB.7 -> H'200E -> H'E826 bit14 -> loc_3E54 queues selector 0x0013
+```
+
+At `H'200E`, the ROM checks `F6DB.7` and requires `F731 <= 3`. It then uses
+`F791.5` as a current-state toggle:
+
+- if `F791.5` is clear, it sets `H'E826.14`,
+- if `F791.5` is set, it clears `H'E826.14`,
+- in both cases it calls `loc_3E54` with selector `0x0013`.
+
+This is not a separate lamp driver. It feeds the same `E800[0x0013].14`
+state consumed by the selector handler.
+
+## Practical Meaning
+
+The strongest current model is:
+
+- CCU/host can drive the lamp directly by sending selector `0x0013` value
+  `0x4000` through command 0.
+- The panel can also toggle/report the same state through a local input lane,
+  but only when the relevant session/page gate is open.
+- No other decoded selector currently appears to directly set the same
+  `F791.5` plus `F716.7` latch pair.
+
+Generated semantics now label selector `0x0013`, `E800[0x0013]`, and the
+`IRIS/M.BLACK LINK` / `SLAVE` bit meanings so pseudo-code output does not leave
+this as a generic table write.