
43
If the value of <expression> is zero or greater than the number of items in the list,
execution continues with the next executable statement. If the value of <expres-
sion> is negative or greater than 255, an error message will be displayed.
ON KEY GOSUB Statement
Purpose:
Defines an interrupt service subroutine to handle specific key-
board input
Format:
ON KEY(<n>) GOSUB <line>
<n> is a numeric expression from one to eight indicating a spe-
cific key.
Example:
ON KEY 1 GOSUB 1000
Remarks:
An interrupt service routine cannot be interrupted by another interrupt. If a new
interrupt occurs during processing of a previous interrupt, branching to handle
the new interrupt will not take place until after the RETURN statement of the first
interrupt service routine is executed.
If a statement specified by the branch line number is non-executable, execution
will begin with the first executable statement following the branch line number.
If zero is specified as the branch line number, it is assumed that the KEY OFF
statement has been executed.
If the port number is omitted, port 1 is selected.
There should be only one ON KEY GOTO statement for each key number.
Key input will not be processed during execution of an assembly language pro-
gram.
The ON KEY GOSUB statement is enabled with the KEY ON statement and dis-
abled with the KEY OFF statement.
Program Example:
10
OPEN #1,“TERM:(42)”
20
ON KEY 1 GOSUB 100
30
ON KEY 2 GOSUB 200
40
ON KEY 3 GOSUB 300
50
KEY ON
100
PRINT A
110
RETURN
200
PRINT B
210
RETURN
300
PRINT C
310
RETURN
Program Remarks:
“A”, “B”, and “C” are displayed by pressing keys 1, 2, and 3, respectively. To can-
cel the specification, write 0 as the branch destination.
ON KEY GOTO Statement
Purpose:
To branch program execution to a specified line number in re-
sponse to a specific key input
Format:
ON KEY<n> GOTO <line>
<n> is an integer in the range of 1 to 8.
<line> is any valid line number.
Commands, Statements, and Functions
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