Assuming you are in serial batch or AppleTalk mode and not the Diablo 630
emulation mode, the following PostScript sequence should issue a restart from
an IBM PC XT:
systemdict/quit get exec
This will need to go into a .bat file for output to the printer port. Do not
forget that the LaserWriter requires XON/XOFF communication with standard
settings of 8 data bits, 1 stop bit, and no parity. If you are using Diablo
630 mode ('special' switch setting), PostScript commands are ignored and
treated as text.