Classic Computer Magazine Archive ANTIC VOL. 6, NO. 12 / APRIL 1988


Trigger Throttle

Easy joystick control online

Trigger Throttle is a short machine language routine designed for modem users who go online with Keith Ledbetter's popular Express! software (version 3.0 or newer). It might work with other modem programs too, either as is or with changes. So let Antic know if you find additional Throttle-compatible software. This BASIC program works on 8-bit Atari computers with at least 48K and a disk drive.

When you're online with one of the big telecommunications services, such as CompuServe or GEnie, you find far more information than you can easily read. Important data often scrolls off the screen before you can read it all.

Most experienced online users know that pressing [CONTROL] [S] will pause the information being sent through the modem. When you're ready to move on, [CONTROL] [Q] will start things again. But it takes a bit of hand-eye coordination to accomplish this. As soon as you see that something important is going to scroll off the screen, you must put your left hand on the keyboard, press the [CONTROL] key and then tap the [s] key. At 300 baud this is generally no problem. But at 1200 baud and especially 2400 baud you probably find that lots of information gets lost or costs you extra money to reread.

I like to sit back and relax while online, especially if I've got a lot of messages to read. On Delphi, for example, I will type the FORUM command READ NEW NS to read new messages nonstop.

If you have played plenty of action games on your Atari, I'm sure your joystick button reaction time is much quicker than your keyboard responses. With Trigger Throttle, I simply press the joystick button to pause the display. Trigger Throttle automatically sends the [CONTROL] [S] character to stop the scrolling. Pressing the button again sends the [CONTROL] [Q] character to resume the scroll.

Type in Listing 1, THROTTLE.BAS, check it with TYPO II and SAVE a copy before you RUN it. When RUN, it will create a machine language file called THROTTLE.EXE. Antic Disk Subscribers will find THROTTLE.EXE on the monthly disk, along with the MAC/65 source code, THROTTLE.M65


From the Atari DOS 2.0 or 2.5 menu, use the [L] option to load THROTTLE.EXE. Trigger Throttle will display some prompts, reminding you how it works. Press [RETURN] to redisplay the DOS menu, then use the [L] option to load the Express! program.

Plug a joystick into port 1 of your 8-bit Atari and start using the trigger button to take control of the bulletin board systems that talk too fast for you. To disable Trigger Throttle, simply press the [RESET] key.


Trigger Throttle is a VBI (vertical blank interrupt) routine. The code that handles the joystick reading and keyboard controls is only 62 bytes. It resides in the lower area of page 1, the system stack, generally recognized as a safe place for very small machine language programs. This leaves page 6 and the lower half of page 4 (the cassette buffer) free for other programs you may add later.

If done properly, many different VBI routines can run on the 8-bit Atari, each chained to the next. So far, Express! 3.0 is the only modem program I have found which follows the proper rules for putting in VBIs and lets me connect the Trigger Throttle program.

$10. 1030 version, PD0081; 850 version, PD0082. The Catalog, 544 Second Street, San Francisco, CA 94107. (800) 234-7001.

This issue kicks off a regular online communications feature by Matthew Ratcliff a St. Louis aerospace engineer who won the 1986 Antic Award for Outstanding Contributor

Listing 2: THROTTLE.M65 Download / View

On Disk: THROTTLE.EXE Download