Commodore PC Ms-Dos 3.2 User's Manual page 302

230 MS-DOS User's Reference
(O)utput
Using the Output
command
Output
Purpose:
Sends the specified byte to the output port specified by value.
Syntax:
Ovalue byte
Comment:
A 16-bit port address is allowed.
Example:
Suppose you want to debug to output the byte value 4F to
output port 2F8. To do this you could simply type the following
command:
02F8 4F
U
U
u
u
u
u
u