$IF ON/OFF

General Form:
    

The $IF ON/OFF statement is used to determine whether the current status of a device is ready or busy.

A device is only considered to be ready if it exists in the device equivalence table, i.e. has been $DEVICEd. An exception to this rule is the device /001 for the keyboard, which exists in the device table but is considered to be ready only if a terminal is attached and a character has been buffered in the keyboard. Similarly the device /005 for the screen is ready only if the terminal is attached.

If $IF ON is used then the command will branch to the specified line number if the device is ready. The branch occurs in $IF OFF statements if the device is not ready.

Syntax examples:

$IF ON #112, 12102
$IF ON <address$>, 2002
$IF OFF /015, 908: ERROR GOTO 9000