Specifications

Chapter 14. Statement Reference
260
Syntax:
ON KEY (keynumber) GOSUB label
Parameter:
keynumber
A numeric expression which returns a value from 1 to 31, 33 to 38, and 501
to 550.
Description:
According to label, ON KEY...GOSUB specifies the first line of an event-handling
routine to be invoked if a function key specified by keynumber is pressed. (Refer
to Appendix E, "Key Number Assignment on the Keyboard.")
•
ON KEY...GOSUB specifies only the location of an event-handling routine but does
not enable keystroke trapping. It is KEY ON statement that enables keystroke
trapping. (Refer to KEY ON and KEY OFF.)
• Specification of zero (0) to label disables keystroke trapping.
• If a keystroke trap occurs, the Interpreter automatically executes KEY OFF state-
ment for the pressed function key before passing control to an event-handling rou-
tine specified by label in ON KEY...GOSUB statement. This prevents a same
event-handling routine from becoming invoked again by pressing a same function
key during execution of the routine until the current event-handling routine is com-
pleted by issuing a RETURN statement.
When control returns from the event-handling routine by a RETURN statement,
the Interpreter automatically executes KEY ON statement.
If it is not necessary to resume keystroke trapping, you describe a KEY OFF
statement in the event-handling routine.
• If you issue more than one ON KEY...GOSUB statement specifying a same key-
number
, the last statement takes effect.
• You can nest GOSUB statements to a maximum of 10 levels.
I/O statement
ON KEY...GOSUB
Specifies an event-handling routine for keystroke interrupt.