QBasic Information Center Tutorials - Events
These tutorials were written to help you get a quick, but thorough, understanding of QBasic -
the scope of the language as well as it's specific capabilities.
Events
QBasic includes a fairly wide range of features which allow it
respond to activity (events) of devices attached to a computer,
via the following statements. Programmers may write code which
is called in response to these events.
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| on strig, strig, stick
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| on key, key
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| on pen, pen
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| on com, com
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| on play, play, beep, sound
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| on timer, timer
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| ioctl, ioctl$
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Status Information
In addition to trapping device events, QBasic can also query
some devices for status information, or control the devices, using
the following statements.
| Joystick | stick(n%) - returns coordinates of a joystick
strig(n%) - returns status of a joystick trigger
| | Light Pen | pen(n%) - returns status of the light pen
| | Speaker | play(n) - returns number of notes in the background music queue
beep - generates a beep sound from the speaker
sound - generates a customized sound from the speaker
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Additional details on these status/control commands are provided in the
reference section below. QBasic's ability to query the
keyboard is covered in a different
tutorial section.
Control Strings
QBasic can also send control string to device software drivers
using the following commands.
- ioctl - sends a control string to a device driver
- ioctl$ - returns status information from devices
These commands apply to devices opened using the QBasic Open
statement, where the assigned filenumber is used to identify
the device to which a control string is to be sent.
Event Trapping Functions Reference
Here's a quick reference of the available event trapping functions, in
alphabetical order.
- ioctl - sends control string to a device driver
ioctl(#1, var$) # var$ is sent to device #1
The device number is that assigned using the Open statement.
- ioctl$ - returns status information from a device driver
result$ = ioctl$(#1) # requests status from device #1
The device number is that assigned using the Open statement.
- on com - enable/disable/suspend event trapping on a comm port
on com(n%) gosub line # trigger an event when a key is pressed
# n% values are 1 or 2, corresponding to serial ports
com(n%) on # enables event trapping for serial port n%
com(n%) off # disables event trapping for serial port n%
com(n%) stop # suspends event trapping for serial port n%
(events are saved and processed later
when event trapping is re-enabled)
- on key - enable/disable/suspend event trapping of keystrokes
on key(n%) gosub line # trigger an event when a key is pressed
n% Key
------ --------------------------------------------
0 All keys listed here (KEY(0) ON, KEY(0) OFF,
and KEY(0) STOP only).
1-10 Function keys F1-F10.
11 Up Arrow key.
12 Left Arrow key.
13 Right Arrow key.
14 Down Arrow key.
15-25 User-defined keys or combination of keys
30, 31 Function keys F11 and F12.
key(n%) on # enables event trapping for key n%
key(n%) off # disables event trapping for key n%
key(n%) stop # suspends event trapping for key n%
(events are saved and processed later
when event trapping is re-enabled)
See QBasic Help for more information on creating user-defined
key events.
- on pen - enable/disable/suspend light pen event trapping
on pen(limit%) gosub line # capture light-pen events
# limit% (1-32) - on play branches to subroutine when
there are fewer than limit% notes in
the music buffer
pen on # enable light-pen event trapping
pen off # disable light-pen event trapping
pen stop # suspend light-pen event trapping.
events are saved and processed when
light-pen event trapping is enabled
- on play - enable/disable/suspend play event trapping
on play gosub line # capture play events
play on # enable play trapping
play off # disable play trapping
play stop # suspend play trapping.
events are saved and processed
when event trapping is enabled
- on strig - enable/disable/suspend joystick event trapping
on strig (n%) gosub line # capture a specific joystick event
# n% values 0 - lower trigger, A
2 - lower trigger, B
4 - upper trigger, A
6 - upper trigger, B
stick(n%) # returns coordinates of a joystick
strig(n%) on # enable joystick event trapping
strig(n%) off # disable joystick event trapping
strig(n%) stop # suspend joystick event trapping.
events are saved and processed
when event trapping is enabled
- on timer - enable/disable/suspend timer event trapping
on timer(n%) gosub line # trigger an event in n% seconds
# n% is seconds until an event is triggered
timer # returns number of seconds since midnight
timer on # enable timer event trapping
timer off # disable timer event trapping
timer stop # suspend timer event trapping.
events are saved and processed
when event trapping is enabled
- play - sends control string to a device driver
beep # no arguments, cannot control duration
- beep - sends control string to a device driver
beep # no arguments, cannot control duration
- sound - plays a sound through the speaker
sound frequency%, duration% # single frequency 37-32,767
# duration is clock ticks
(10.2 ticks per second)
If you have any suggestions or corrections, please let me know.
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