Re: Microsoft Z-80 Card on Apple II+

[mjmahon@aol.com (Michael J. Mahon)]

In article <20030402080603.23178.00000614@mb-fh.aol.com>, quadrajet1@aol.com
(Quadrajet1) writes:

><< >   The reason I thought the AE card may work is it was made a lot later
>than the
>> MS card.  Plus if I recall they made 2 versions, one with a red LED and one
>> with a green LED.  I think one was 4 Mhz, the other was 6?
>
Steven N. Hirsch replied:
>
>>No.  They were all MS knockoffs and ran at an effective 2Mhz.  You may 
>>be getting thrown by the speed rating of the CPU chip, which has nothing 
>>to do with how it actually operates in circuit.
>
>  I beg to differ, there was 2 different versions of the AE Z80 card.  I'd
>have
>to do some research on that, but most of my materials from that era is
>buried.
>We used to sell them back when they were new.  AE never really knocked
>anything
>off, they made it better.  I have seen Taiwan knockoffs that even copied the
>silkscreen so the card would still say Microsoft (or whatever) on it.  But
>you
>could tell a mile away from the quality of the workmanship.

I do not have an AE Z80 card, but I suspect that what Steven meant
by "knockoff" is that the AE cards use the same address mapping
and clocking scheme.  This would make them "compatible" with
the SoftCard, but also susceptible to the same bus timing issues.

The SoftCard ran all Z80-generated addresses through an adder to
add $10 to the high-order byte.  This is how the distinctive Z80 "view"
of the Apple II address space was generated.  The extra time for this
add came out of the address setup budget, and required both fancy
footwork on the Z80 timing and, apparently, pushing the margins on
the peripheral bus to work.  All cards which use a similar address
mapping scheme may have problems with later implementations of
the Apple II peripheral bus.


-michael

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