Apple II Computer Info
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### FILE : paddles.info
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### Created : Sunday, January 14, 1996 Modified: Sunday, January 14, 1996
### File Type: "TEXT" File Creator: "LMAN"
### File Size: 3336 bytes 3 KB
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Newsgroups: comp.sys.apple2
Path:
news.weeg.uiowa.edu!news.uiowa.edu!uunet!orca!javelin.sim.es.com!animal!mmunson
Subject: Re: Joystick readings from ML
Nntp-Posting-Host: animal.sim.es.com
Organization: Evans & Sutherland Computer Corp., Salt Lake City, UT
Date: Mon, 5 Oct 1992 21:17:58 GMT
Lines: 67
Shane:
Unfortunately, there isn't another ROM based routine for reading the joysticks.
You'll have to write your own in machine language. It might seem like a
problem, but it's really easy once you see it done.
First, you need to know what the paddle (joystick) hardware is doing. When
you strobe the paddles, a charge is applied to a capacitor. A variable
resistor (paddle) allows the capacitor to discharge to ground. By measuring
the time for this to occur, you can guage the setting of the paddle.
The ROM based paddle routines use the Apple II running at 1 MHz, with a known
paddle resistance in the 0 to 150 ohm range (or was that 150 K-Ohm?) Even on
a GS, the call still slows the machine down during this timing sensistive
process.
Strobing the paddles, starts the process on all of the 4 possible paddles.
If the paddle you are reading finishes quickly, and you try to read the
next paddle (which hasn't finished), you will get faulty values for the
second paddle.
Example:
PDL 0: +-----------!
PDL 1: +----------------!
_____________________________
0 100 200 255
In the example above, you would get a value of 100 for PDL(0). If immediately
try and read PDL(1) before it has a chance to finish, then you might get a
value of 50 {150 - 100} for PDL(1).
A cheap way to correct for this is to check the paddle switch location to insure
that the paddle has timed out before you strobe the paddle. It works, but it
wastes time. There is a faster way to get both paddle values, without running
Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 328 of 572
(22 pages)
(16 pages)
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