A Solid-State Drive for the ][+

[robsgreenneon@startmail.ca (Rob Jones)]

I was looking at my Apples, and thought to myself, "Would it be
possible to use some form of permanent memory like an EEPROM or
battery-backed RAM to build a solid-state drive for the Apple ][+"? I
have seen the possibility of using IDE Hard Drives and CFFA cards to
do this, so why not regular memory?

The problem that arises is figuring out when and how DOS communicates
a Read from or Write to disk. I started looking at the disk
controller: I have an Elite controller which can drive up to 4 drives,
and with a modification to DOS 3.3, will access up to 560K (DS/DD)
disks (providing an Elite 3 drive is attached).

So I started thinking, what signals are present at the 20-pin
connector between the controller and the drive? I quickly went to the
manuals and discovered that the controller uses 5 data signals between
it and the drive: RD Data, WR Data, WR Req, /Enbl1, and /Enbl2. There
are 4 signals, which I assume are the drive selects, labeled as o0,
o1, o2, and o3 (driven by Q0 through Q3 of a 9334 chip). If I was to
use this control, with some logic, I could select several banks of
560K, each representing one disk.

The other possibility is to completely bypass the disk controller and
have a ML subroutine issue the read or write command at the bus. This
way I could use the Apple address lines to directly access the RAM. I
would need to find a way to separate main RAM from this add-on RAM,
but a latch to trap an 8-bit data word at a specific address location,
would tell the RAM Disk where to look for the data, and then transfer
it into the APPLE's memory.

Can this be done?

~Rob J.