STOP+A works with a directly attached keyboard being used in conjuction with a directly attached monitor.
If you don't have a monitor and keyboard the system will use the serial port as the console. If that serial port receives a BREAK signal, the system will respond the same way as STOP+A works. You don't use the shift or control keys with the break signal. Break is not a character.
If your pc keyboard is plugged into a pc and that pc is connected to the serial port of the sparc then the pc must be running hyperterminal or something. These terminal emulators all have a way to send a break signal out the serial port. If that is not the case, switch to a better terminal emulator.
If your pc keyboard is directly connected to the sparc you should really get another keyboard. But I think that unplugging and reconnecting the keyboard should work.
Whether or not any of this works depends on keyboard aborts being enabled. This is the default, But they may be disabled on your system. If there is a line like:
KEYBOARD_ABORT=disable
in the file /etc/default/kbd then keyboard aborts are disabled. In this case you can re-enable them with the kdb command. You can edit that file and run "kbd -i". Also you can make a one-time change with commands like "kbd -a enable" and "kbd -a disable". There is more to know about this kbd file and command. See
the man page.
Also see
this doc which mentions another way to disable keyboard aborts. I think that this is now deprecated in favor of the kbd stuff, but you could still have it set.
Finally, some sparcs have a hardware switch to disable keyboard aborts. So check the docs for your hardware.
