@nataliapc/mcp-openmsx/resources/programming/basic_wiki/ON_KEY_GOSUB.md

Model context protocol server for openMSX automation and control

# ON KEY GOSUB

## Effect

Defines a subroutine to execute when a function key is pressed down.

This 'rule' is activated only when the function key is enabled.

## Syntax

`ON KEY GOSUB <LineNumber>,<LineNumber>,<LineNumber>...`

_Note: Each parameter is optional except the last specified. Do not put a comma after this parameter._

## Parameters

`<LineNumber>` is a program line number of subroutine that will be called when the corresponding function key is pressed. We can put until 10 line numbers behind `GOSUB` (one per function key). If there is no matching line number no `GOSUB` will be made.
The subroutines must be terminated with the `RETURN` instruction.

## Example

```basic
10 FOR I=1 TO 3: KEY(I) STOP: NEXT ' F1 to F3 are stopped
20 FOR I=4 TO 10: KEY(I) OFF: NEXT ' F4 to F10 are disabled
30 ON KEY GOSUB 170,180,190 ' Subroutine will only be active from line 130
40 CLS
50 PRINT"TEST 1: No effect"
60 PRINT
70 PRINT"Press a function key or ESC key"
80 A$=INPUT$(1)
90 IF A$=CHR$(27) THEN 100 ELSE 80
100 CLS
110 PRINT"TEST 2"
120 PRINT"Press a function key"
130 KEY(1)ON: KEY(2)ON: KEY(3)ON ' F1 to F3 and the subroutine in line 30 are enabled
140 GOTO 160
150 PRINT:PRINT a$+" pressed"
160 GOTO 160
170 A$="F1": RETURN 150
180 A$="F2": RETURN 150
190 A$="F3": RETURN 150
```

Each line number after `ON KEY GOSUB` refers to a specific function key according its position in the instruction.

## Related to

`KEY`, `KEY()`, `RETURN`

## Compatibility

MSX-BASIC 1.0 or higher

## Source

Retrieved from "https://www.msx.org/wiki/ON_KEY_GOSUB"