Document -n behaviour wrt -U and terminal

src/avrdude.1

@@ -586,9 +586,10 @@ written to
 .Va stderr
 anyway.
 .It Fl n
-No-write - disables actually writing data to the MCU (useful for debugging
+No-write: disables writing data to the MCU whilst processing -U
+(useful for debugging
 .Nm avrdude
-).
+). The terminal mode continues to write to the device.
 .It Fl O
 Perform a RC oscillator run-time calibration according to Atmel
 application note AVR053.

src/doc/avrdude.texi

@@ -667,8 +667,8 @@ Note that initial diagnostic messages (during option parsing) are still
 written to @var{stderr} anyway.
 
 @item -n
-No-write - disables actually writing data to the MCU (useful for
-debugging AVRDUDE).
+No-write: disables writing data to the MCU whilst processing -U (useful for
+debugging AVRDUDE). The terminal mode continues to write to the device.
 
 @item -O
 Perform a RC oscillator run-time calibration according to Atmel

src/main.c

@@ -241,7 +241,7 @@ static void usage(void)
     "                             Memory operation specification\n"
     "                             Multiple -U options are allowed, each request\n"
     "                             is performed in the order specified\n"
-    "  -n                         Do not write anything to the device\n"
+    "  -n                         Do not write to the device whilst processing -U\n"
     "  -V                         Do not verify\n"
     "  -t                         Enter terminal mode\n"
     "  -E <exitspec>[,<exitspec>] List programmer exit specifications\n"
@@ -1471,6 +1471,8 @@ int main(int argc, char * argv [])
     /*
      * terminal mode
      */
+    if (uflags & UF_NOWRITE)
+      pmsg_warning("the terminal ignores option -n, that is, it writes to the device\n");
     exitrc = terminal_mode(pgm, p);
   }