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From: ranger@ecsvax.UUCP (Rick N. Fincher)
Newsgroups: net.micro.apple
Subject: Re: Apple IIe and IIc raster scan synchronization.
Message-ID: <2083@ecsvax.UUCP>
Date: Tue, 30-Sep-86 12:41:13 EDT
Article-I.D.: ecsvax.2083
Posted: Tue Sep 30 12:41:13 1986
Date-Received: Fri, 3-Oct-86 00:44:54 EDT
References: <2869@sdcc6.ucsd.EDU>
Organization: UNC Educational Computing Service
Lines: 13

> I need to synchronize a program with some fixed point in the video
> display cycle (i.e. raster scan) on IIe's and IIc's.  I have done
> this on II+'s by wiring a certain pin into the game port, and then
> reading the status of the game port.  I would like to do the same
> thing for the other II machines, but I don't know which pin it is

The //e and //c have a soft switch that indicates vertical retrace to software.
The signal is also on the bus slots.  I don't remember which pin.  You
can look up the address of the soft switch or the bus pin in the //e reference
manual.  These signals should be          
available in the //c somewhere too, although I don't know where.  The mouse hardware built into the //c can generate an interrupt on vertical retrace,
even if you don't have a mouse connected.  So you can write an interrupt
routine to do whatever you want at that time.