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Path: utzoo!watmath!clyde!burl!ulysses!mhuxj!houxm!ihnp4!inuxc!pur-ee!ecn-ee!dunkelbe
From: dunkelbe@ecn-ee.UUCP
Newsgroups: net.micro.cbm
Subject: Re: C64 Mouse
Message-ID: <2207@pur-ee.UUCP>
Date: Thu, 4-Oct-84 03:36:20 EDT
Article-I.D.: pur-ee.2207
Posted: Thu Oct  4 03:36:20 1984
Date-Received: Fri, 5-Oct-84 05:31:22 EDT
Sender: notes@pur-ee.UUCP
Organization: Electrical Engineering Department , Purdue University
Lines: 27
Nf-ID: #R:zinfandel:19800012:ecn-ee:19300005:000:1047
Nf-From: ecn-ee!dunkelbe    Oct  3 10:47:00 1984



The C64 has two pot inputs on the video chip which are most
consistantly read by syncing with the video.  In other words,
always check the raster register and read on the same line of
video to prevent jitter on the value read back from the analog
inputs.

If the RS mouse is like any of the others I have seen, it will
be sending pulses down the switch oriented joystick lines just
as if the user was repeatedly moving the joystick one of the
four directions and letting it come back to center.  I would
be surprised if the mouse had any type of pot action since all
software would have to take into account the wrap-around for
every rotation of the wheel.

The programmer's reference manual has all the info you need.
For the pot interface, refer to the VIC chip description section.
The joysticks are connected to a parallel port which normally
runs the keyboard.  With a little bit of machine language
programming, you could get a neat little interrupt driven mouse
routine for $40.

			Kirk Dunkelberger
			pur-ee