Re: How do I add firmware to a card?

[dempson@actrix.gen.nz (David Empson)]

RedskullDC <RDC@oz.org> wrote:

> "David Empson" <dempson@actrix.gen.nz> wrote in message 
> 1hsc1jh.1hqbl6aapwbr5N%dempson@actrix.gen.nz">news:1hsc1jh.1hqbl6aapwbr5N%dempson@actrix.gen.nz...
> > <aiiadict@gmail.com> wrote:
> 
> > I don't recall whether the 65C02 in the UniDisk 3.5 runs at a higher
> > clock speed than the Apple II: if data is transferred between the
> > UniDisk CPU and the 3.5" drive mechanism under processor control then it
> > would need to run at about 2 MHz (or faster) to be able to keep up with
> > the data rate (16 microseconds per byte, which is twice as fast as a
> > 5.25" drive). If they used some form of DMA, then the UniDisk's CPU
> > could be running at the same clock speed as the Apple II.
> 
> The IIgs firmware manual covers the smartport calls , and the internal
> memory map for the 65C02 in the Unidisk3.5.
> 
> It uses an IWM chip which is clocked at 7MHz to achieve the 16ms/byte
> you mention.

The IWM always runs at 7 MHz in any Apple II (or equivalent), or at 8
MHz in a Mac. It isn't the IWM that has trouble with 3.5" double density
bit cell timing - it is the inability of a 1 MHz 65C02 to transfer data
quickly enough between the IWM and RAM.

> The 65C02 is running at 2MHz.

Right, so that makes it slightly more meaningful to use one as a
coprocessor, as long as the task involves transferring blocks of data no
larger than about 1 KB at a time (less if any temporary memory is
required).

Thanks for filling in the details.

-- 
David Empson
dempson@actrix.gen.nz