Re: HD20

[Stephen Shaw <xstephenx@apple2.org.za>]

On Tue, 19 Mar 2002 12:41:14 +1200, David Empson wrote:

> Stephen Shaw <xstephenx@apple2.org.za> wrote:
>
>> On Thu, 14 Mar 2002 12:39:52 +1300, David Empson wrote:
>>
>> > The biggest hurdle is that the Mac and Apple II use pin 10 of the disk
>> > connector for different purposes.
>>
>> David, I'd just like to clarify something. The 'early' (first ?) Mac uses
>> an IWM chip. Is this the same as the IIc IWM chip? Or if you use the Mac IWM
>> chip in the IIc can you just bend pin 10 up when you socket it?
>
> I was talking about the physical disk interface (the D19 connector), not
> the IWM chip.
>
> The Mac 128 through Mac Plus have a 28 pin DIL package IWM chip which is
> identical to the one installed in the IIc.  It is soldered onto the
> motherboard.  The SE and Mac II probably use the square pack version in
> a socket, which can be upgraded to the SWIM chip.  Later models have a
> SWIM chip as standard.

Yahoo I have some spare ASICs then. Thanks David. I was told by a so called
Apple expert at the time I was collecting those motherboards that the 2 chips
were different. I was sceptical as my reasoning was then Apple would have 
given the chip another part number. Again thanks David.

>
> The IWM chip is not responsible for all the signals on the disk
> connector.  A few of the incidental control lines (e.g. head select for
> 3.5" drives) are implemented through I/O peripherals controlled directly
> by the CPU (e.g. the VIA chip in the case of the Mac).

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