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From: rainer@boulder.Colorado.EDU (Rainer Malzbender)
Newsgroups: comp.sys.m68k
Subject: Re: HELP HELP HELP on some Technical Questions for the 680000!!!
Message-ID: <1991Apr2.220648.23079@colorado.edu>
Date: 2 Apr 91 22:06:48 GMT
References: <1991Apr02.174845.5076@lynx.CS.ORST.EDU>
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In article <1991Apr02.174845.5076@lynx.CS.ORST.EDU> rudolpe@prism.CS.ORST.EDU (Eric Rudolph) writes:
>
>I need to know about how VPA* VMA* E* and AS* are related. I have one
>timing diagram for them and a little chart that tells the relative
>timings, but I need to know WHAT they do and how they relate in English.
>Things like "what would happen if the device didn't assert VPA" and 
>"Why does the 68k assert VMA* and how does it relate to VPA*" stuff like
>that.... I would be very grateful. I am designinga the famed speedup circuit
>for the Amiga....

VPA, VMA, and E are used to interface to older 6800-style peripheral chips.
E is a clock that is the CPU clock divided by 10. VPA and VMA mean "valid
peripheral address" and "valid memory address" (I think - all my hardware
manuals are at home). They basically inform the 68000 that it is talking
to a 6800 peripheral. I could dig up the databook later, but I'm almost
positive you don't have to worry about these signals at all if you're
designing for the Amiga. On my 68000 designs I never use VPA and VMA;
sometimes I use E if I need a slower clock. BTW, is the "famed speedup
circuit" a 68030 or something ?

--
Rainer Malzbender                                 Save a dinosaur - buy DEC.
Dept. of Physics (303)492-6829
U. of Colorado, Boulder         rainer@boulder.colorado.edu 128.138.240.246