Epson EL 486UC - Manual (Page 43)

Note
You can use the commands listed above while you are
running a program. However, if the program uses one of
these commands for another function, you cannot use it to
change the processor speed. You can, however, change the
processor speed through the SETUP program.
The speed setting remains in effect until you do the following:
Reset your computer
Turn off your computer
Change the speed with another keyboard command
Change the speed setting in the SETUP program.
2-6 Using Your Computer