OIS 140 IDE Interface
This interface uses a different approach than the one I built for the 125A.
The 8255 interface chip has been eliminated, so the IDE device is connected
directly to the Data Bus through a buffer (74LS245). The IDE device's registers
appear at 0c90-0c97.
I observed several problems with certain disks connected to this interface.
The older the disk, the higher chance that it would not work. The two disks
I have had good results with so far are a Conner CP30544 (540MB) and a Seagate
1.0GB drive.
Either my regulator board is bad, or the +12v does not source much current.
I had to use an old PC power supply for the disk drive, and tied the ground
to the OIS ground.
The board is wired point-to-point on a prototype PCB, and I used a hole
that already existed in the 7502 floppy controller board to attach it with
a plastic screw. The other three holes in the proto board have cut-off PC
motherboard standoffs in them. Note that you cannot put a 7685 CPU board
in the system when this is installed - there is not enough room.
I have a modified Starter 1 disk that puts you right into the Debugger.
You have to patch the system with the hard disk parameters, so I use this
to load the image to an extra workstation, edit it, and write it back to
the Starter 1 disk. Then, the system can be restarted, and the new hard disk
can be initialized.
If all goes well, you can initilaize the system disk. I have it patched
in as Drive Address 14, which is the 3MB Shugart drive. Even though it will
say '3 Megabytes capacity', it will actually initialize and use whatever number
of sectors you configure. For testing, I usually set the number of cylinders
to a small size (equals about 20MB).
So far, so good....
When you are all done, you should be able to see this...
