Relocated monitor to top 16k

README.md

@@ -1,7 +1,14 @@
 # Z80 UART monitor
 
 This ROM provides a small interactive monitor on the UART/CTC card at I/O base
-`20`. Connect a terminal at **2400 baud, 8 data bits, no parity, 1 stop bit**.
+`20`. At reset, a small ROM bootstrap copies the monitor into the top 16 KiB of
+RAM at `C000-FFFF` and starts it there. Only the occupied vector/code bytes are
+stored and copied; uninitialized data is cleared directly in high RAM. The low ROM can subsequently be disabled
+without taking the monitor, its data, or its interrupt table away. Runtime code
+and vectors occupy the lower part of this window, globals begin at `F000`, and
+the stack grows downward from `FFFF`; no RAM below `C000` is used.
+
+Connect a terminal at **2400 baud, 8 data bits, no parity, 1 stop bit**.
 Commands are case-insensitive and all numeric arguments are hexadecimal; an
 optional `0x` prefix is accepted.
 
@@ -26,4 +33,12 @@ make
 ```
 
 The outputs are `build/metal/monitor.bin` (32 KiB ROM image) and
-`build/metal/monitor.prog.bin` (compact programmer image).
+`build/metal/monitor.prog.bin` (compact programmer image). The ROM layout is:
+
+- `0000-007F`: reset/copy bootstrap
+- `0080...`: compact vector/code image copied to RAM starting at `C000`
+- Remaining bytes: unused and available for additional ROM content
+
+The monitor executable starts at `C080`; its IM 2 vector table is at `C040`.
+`monitor.prog.bin` ends immediately after the occupied payload, while
+`monitor.bin` remains a complete 32 KiB chip image.