Re: Who has IIc ROM that allows plat 3.5" 800K drives???

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

stephen e buggie <buggie@ben16.unm.edu> wrote:

> Someone recently bragged that they have a IIC PLUS ROM chip that allows
> the _platinum_ 3.5" 800K drives to be operated on the ordinary IIC.

Sorry, this is either someone who is pulling your leg or they have
absolutely no idea what they are talking about.

The IIc hardware is phyiscally unable to access the Apple 3.5 Drive,
because it is not fast enough.  It needs to be able to read or write a
byte every 16 microseconds.  The 1 MHz 6502 or 65C02 can keep up with 32
microseconds per byte for the Disk ][ or UniDisk 3.5, but nothing
faster.

It _might_ be possible with a ZIP chip, provided you can disable the
slowdown when accessing the slot 6 hardware (and this would have to be
turned back on for accessing 5.25" drives).

Even then, it almost certainly won't work because the extra signals
required to control the Apple 3.5 Drive are not available (head select,
3.5" drive enable).

The IIc+ has a special ASIC chip that provides access to the Apple 3.5
Drive, by doing the high-speed operations in hardware.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand