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Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!tektronix!orca!shark!kellym
From: kellym@shark.UUCP (Kelly McArthur)
Newsgroups: net.micro.amiga
Subject: Re: Memory/clock expansion for the Amiga (7/9 - mem.sch)
Message-ID: <1701@shark.UUCP>
Date: Fri, 13-Jun-86 13:23:27 EDT
Article-I.D.: shark.1701
Posted: Fri Jun 13 13:23:27 1986
Date-Received: Tue, 17-Jun-86 09:20:15 EDT
References: <1021@umd5.UUCP>
Reply-To: kellym@shark.UUCP (Kelly McArthur)
Organization: Tektronix, Wilsonville OR
Lines: 38
Keywords: Nonconformance to Specifications...

In article <1021@umd5.UUCP> louie@trantor.umd.edu (Louis Mamakos) writes:
>
>
>
>                  2/4 74125 [D4]
>          2 |\ 3                              5 |\ 6
>  HOLD* ----| >----[66] DTACK*      ADR*---+----| >------[18] XRDY
>            |/O                            |    |/O
>             1|                            |      | 4
>              |                            +------+
>              +--- ADR*

To quote from document "Designing Hardware for the Amiga 
Expansion Architecture":

   2.2.1  Read or Write Cycle with Amiga as Master

   Since the Amiga bus master is a 68000, the bus cycle is a 68000
   cycle. However, the responding slave does not pull DTACK*. Our
   internal circuitry will pull DTACK* unless the slave pulls XRDY
   low.

Elsewhere, in the document "INTERFACING TO THE 68K CONNECTOR 
ON THE AMIGA", it states:

   2.2 Bus Timing

   ...Two control inputs, VPA* and DTACK* are driven by logic on 
   the Amiga and should not be driven by your circuitry.

Since in the above schematic, DTACK* is shown as being driven
by a '125 under some condition it appears likely that this
could result in a tri-state contention over DTACK*. This is 
not good. A few changes to the XRDY* logic would eliminate
the need for that driver all together.

                                      Kelly McArthur
                                   ...tektronix!shark!kellym