use F5 key on Digital VT320 terminal to send BREAK
from http://www.cs.utk.edu/~shuford/terminal/dec_keyboards_news.txt

STOP + A on sun keyboard BREAK

change serial port
setenv output-device ttyb
setenv input-device ttyb
reset
back to screen + keyboard
setenv output-device screen
setenv input-device keyboard
reset
from http://www.gentoo.org/doc/en/gentoo-sparc-obpreference.xml