[rescue] newest rescue

[Mike Spooner]

Perhaps the 68000 *ISA* was inspired by the PDP-11, but the memory-mapped
I/O and bus control-signalling were inspired directly by the 1970s Motorola
8-bit 6800 family.

Many of the Motorola 68000 peripheral chips (68230 parallel i/f, 68681
DUART, 68901 multi-function i/f and interrupt controller, 6859 DES security
device, etc etc) could be *directly* used with existing 6800/6809/6811/etc
CPUs, and to an extent (speed permitting) vice-versa - almost all the
6800-series peripheral chips (6847 video display generator, 68488 GPIB i/f,
etc, etc) could be *directly* used with the 68000, as long as the bus speed
was low enough; the 1970s-designed 6800 peripheral chips were usually rated
for maximum bus-clock of either 1MHz, 1,5MHz (NMOS) or 2MHz (HCMOS).

Motorola's own EVB and EVM evaluation boards for the 8-bit 68HC11 came with
a (68000-series) DUART controller on-board.

It was no accident that the bus-control interface of the 6800 series and
68000 were identical.

Back on the ISA, the 68000 sure was pretty orthogonal and easy to progam
for; the separate address-registers and data-registers was a bit of a
cop-out, but at least memory-addressing-modes could be freely used with
either (except for some bit-addressing modes).

On the other hand, it was not as orthogonal as the roughly contemporary
32-bit NatSemi 16032 (later renamed 32016!), where any operand could be any
register, any memory-addressing-mode, or any size of immediate - a truly
insane dedication to utter orthogonality, and damn the cost.

-- Mike Spooner
http://mbus.sunhelp.org


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>
> Message: 1
> Date: Tue, 2 Feb 2016 19:53:01 -0600
> From: Lionel Peterson <lionel4287 at gmail.com>
> To: The Rescue List <rescue at sunhelp.org>
> Subject: Re: [rescue] newest rescue
> Message-ID: <DF4ACC71-F24B-4B49-B564-CF2CF0591192 at gmail.com>
> Content-Type: text/plain; charset=us-ascii
>
> Didn't one 'inspire' the other architecture?
>
> Lionel
>
> > On Feb 2, 2016, at 7:18 PM, John Hudak <jjhudak at gmail.com> wrote:
> >
> > The 68030 cpu was,
> > as a CISC architecture, very good. It was analogous to the PDP11 CPU hw
> > architecture at the time.
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 2 Feb 2016 21:10:43 -0500
> From: John Hudak <jjhudak at gmail.com>
> To: The Rescue List <rescue at sunhelp.org>
> Subject: Re: [rescue] newest rescue
> Message-ID:
>         <
> CAPFCoiuPhD+R3s8rkERLFhYd+RwCn9tCFWjUaNszu_3e4h50Pw at mail.gmail.com>
> Content-Type: text/plain; charset="us-ascii"
>
> IDK if it was ever stated but, one could make the argument that the 68K was
> inspired by the PDP11 ISA and the memory mapped I/O.  Some ppl have said
> that the 32-bit 68K was the 'extension' of the 16bit PDP11...there are some
> similarities and also differences.  DEC would argue that the vax (virtual
> address extension) was the extension of the PDP11, e.g. a machine with a
> memory space that would take it 25 years to outgrow (according to the
> design requirements of the time).  I don't agree with that, in that
> learning the VAX assembly language gave me a real headache - no way could I
> remember all the different seemingly different bit settings....Not as easy
> compared to the PDP11 ISA.
>
>
> On Tue, Feb 2, 2016 at 8:53 PM, Lionel Peterson <lionel4287 at gmail.com>
> wrote:
>
> > Didn't one 'inspire' the other architecture?
> >
> > Lionel
> >
> > > On Feb 2, 2016, at 7:18 PM, John Hudak <jjhudak at gmail.com> wrote:
> > >
> > > The 68030 cpu was,
> > > as a CISC architecture, very good. It was analogous to the PDP11 CPU hw
> > > architecture at the time.
> > _______________________________________________
> > rescue list - http://www.sunhelp.org/mailman/listinfo/rescue