Path: utzoo!mnetor!uunet!yale!husc6!bu-cs!spike
From: spike@bu-cs.BU.EDU (Spike)
Newsgroups: comp.sys.apple
Subject: Re: 60 Hz interrupt mod
Message-ID: <21947@bu-cs.BU.EDU>
Date: 22 Apr 88 20:07:48 GMT
References: <8804211832.aa02388@SMOKE.BRL.ARPA>
Reply-To: spike@bu-it.bu.edu (Joe Ilacqua)
Followup-To: comp.sys.apple
Organization: Boston University Distributed Systems Group
Lines: 42

In article <8804211832.aa02388@SMOKE.BRL.ARPA> PGOETZ@LOYVAX.BITNET writes:
<
<   This is written for the Apple II and II+.  NOT the IIe, which I have heard
<can generate interrupts itself anyway. 

	On the //c (and most likely the //e) it is call the Vertical
Blanking Interrupt (VBL).  It can be set by reading or writing $C05B and
disabled by reading or writing $C05A.  It is used by the mouse
firmware, so take care in using yourself.  

	The //c also has a Keyboard interrupt and do keyboard
buffering... To turn it on:
		sei		;Disable interrupts
		lda #80
		sta $05FF	;Where to put next char
		sta $06FF	;An where to read from
		lda $C0AA	;Turn on the ACIA 
		ora #$0F	;(The serial chip in port 2)
		sta $C0AA
		cli 		;enable interrupts

	Programs should read the buffer by calling $FD0C (RdKey).  ^S
and ^C will not work with buffering on.  Nor will auto-repeat.
Closed-Apple-^X will flush the buffer.


<	Note that if you write an interrupt handler which takes more
>than 1/60 of a second, you will be caught in an infinite loop.

	In many cases it is best to turn off interrupts (sei) at the
start of your routine and enable them as you exit (cli).

	The GS //c and //e use interrupts for a number of thing, it
best to check the Tech. Refs to see what it handles and what it will
past to you to handle...

       "You'll laugh, you'll cry, you'll kiss 3 bucks goodbye."
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