Who has IIc ROM that allows plat 3.5" 800K drives???
stephen e buggie
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.
I want it! If this rom does what was say, it will invigorate the
platinum 3.5" drive resale market, and also restore interest in the IIC!
There are just not enough Unidisk 3.5" white drives to satisfy the IIc
users. They are scarce and expensive. But platinum 3.5 drives are
abundant and cheap.
Gimme this rom, and my trusty eprom burner will create enough to make all
IIC users happy! Steve Buggie
Stephen Buggie |"Idleness is pleasant,|
Psychology Dept. | but its consequences |
Univ. of New Mexico, Gallup | are cruel." |
200 College Rd. | (Pres. John Quincy |
Gallup, NM 87301 | Adams, c1830) |
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** bug...@unm.edu voice: (505) 863-7504 or 863-2390 **
** IIgs/IIc/IIe loyalist **
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David Empson
> 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
dem...@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand
David Wilson
>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.
I find this difficult to believe.
1) Pin 4 of the disk port is Gnd on a //c while it is 3.5* (3.5"
disk drive select) on the //c+ and //gs.
Pin 9 is EXTINT* on a //c while it is ENBL* (drive 2 enable)
on a //c+.
2) The //gs is able to run Apple 3.5" disk drives because it runs
faster than 1MHz. The //c+ is able to run Apple 3.5" disk drives
because of additional hardware (Multidrive Interface Glue + 2KB
RAM chip).
At a guess, to get a //c to run an Apple 3.5 you would need to create the
3.5* signal, install a Zip chip or equivalent and then rewrite the disk
driver routines in ROM.
If it were possible, why did Apple have to add extra hardware to the //c+
(especially as it has an accelerator onboard)?
--
David Wilson School of IT & CS, Uni of Wollongong, Australia da...@uow.edu.au
David Empson
> At a guess, to get a //c to run an Apple 3.5 you would need to create the
> 3.5* signal, install a Zip chip or equivalent and then rewrite the disk
> driver routines in ROM.
There is also the head select signal, which is controlled by software in
the IIgs. It goes to another pin on the drive connector (16).
> If it were possible, why did Apple have to add extra hardware to the //c+
> (especially as it has an accelerator onboard)?
The accelerator was apparently an afterthought - they had already
designed the 3.5" drive ASIC by then. If the accelerator had been
planned from the beginning, they could have used much simpler hardware
support for the 3.5" drive.
Obsbedia2
Randy Shackelford
: Let me get this straight: my IIc+ CAN run an external platinum 3.5 drive?
Yeppers. The internal is a grey 3.5 in essence even.
--
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