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From: Dick@cup.portal.com (dick a wotiz)
Newsgroups: comp.sys.apple
Subject: Re: Apple 2e doesn't see my 6522's !!
Message-ID: <21981@cup.portal.com>
Date: 8 Sep 89 04:36:28 GMT
References: <8909060935.aa25446@SMOKE.BRL.MIL>
Distribution: usa
Organization: The Portal System (TM)
Lines: 15

> I'm having this trouble with a parallel interface I'm building for my //e. I
> have some experience building things (MIDI-interface, RS-232, sound, you know)
> and have never had any trouble. Now I'm working on a card consisting of 2 VIAs
> (6522) and I just can't get it to work !!

I remember running into this a while back...  I seem to recall that
the 6502 applies the address and R/W signals at the start of phi0,
but the 6522 latches these lines on the same rising edge.
What I did was delay phi0 by a small amount, by running it through
four sections of a 74LS04 inverter before running it to the 6522.
That way, the 6522 had enough set-up time on the address lines
before latching them in.  You could probably get away with a
RC delay also, if you don't have enough spare gates to use.

Dick Wotiz                                    dick@portal.com