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View Full Version : Bring up IMSAI 8080, Versafloppy and Micropolis 1053



kleindi
March 7th, 2012, 07:26 AM
Hi,

i'm new at this forum. I owned an IMSAI 8080 in terrbible status a few month before. The powersupply, mainboard, CPA, original IMSAI CPU 8080, and memory board are running well now.

I also got an SD Systems Versafloppy I with this System.
http://s100computers.com/Hardware%20Folder/SD%20Systems/VersaFloppy/SD%20Systems%20Versafloppy.htm

So the next step should be to integrate a terminal port and a disk system. I bought an IMSAI MIO board like:
http://s100computers.com/Hardware%20Folder/IMSAI/MIO/MIO%20Board.htm

and an Micropolis 1053-II dual disk drive.

As i'm in Germany and the items are ordered in the U.S. delivery will take a few day.

In the meantime i collect some information about the CP/M system and found in some old documentation a BIOS for the Versafloppy I controller. This is compiled now and saved in an eprom.

Unfortunately i'm unsure, if the controller and the will disk drives fit. I found the information that the micropolis drives are hard sectored and the Versafloppy I with it's 1771 is soft sectored compatible. I don't understand if this means that the controller is able to handle both, or just soft sectored. As the controller is able to handle 8" and 5.25" drives i would expect that it's also able to handle hard sectored drives. But i found no information about this.

Can someone provide some information about this combination?

Also i found in a descrition from an old Siemens floppy drive that the sector signal is forwarded to the sector signal and the index is created by a counter of the sector signal. So can i modify the drives to soft sectored if I bypass the

Has anyone a schematic of these drive an can provide this to me?

Thanks in advanced,
Dietmar

MikeS
March 7th, 2012, 07:46 AM
I don't know of any soft sector controllers that can also deal with hard sectored disks. On the other hand, although many if not all Micropolis controllers were hard-sector, I don't think the Micropolis drives care one way or the other whether the disks are hard- or soft-sectored; extracting the index pulse from the sector pulses was done on the controller.

Assuming all other issues are taken care of, AFAIK your combination should work.

Unfortunately my .pdf of the Micropolis service manual is corrupted; if you find a good copy, please post a link here.

Good luck!

Chuck(G)
March 7th, 2012, 09:03 AM
It's not a matter of hard or soft sector. The 1053s are 100 tpi, 77 track. You'll have to use one of those or a compatible drive (e.g. Tandon TM100-4M) to write a boot floppy. Also, the pinout on the connector is slightly different from the Shugart SA400 standard, mostly in the area of where READY goes and the drive selects.

kleindi
March 7th, 2012, 10:26 AM
@MikeS
That's a nice idea. Up to now, I only thought about using soft sctored disk. But then the counter will not work. But of course you're right, the index should work by using hard sectored disk.

@Chuck(G)
I'm aware about the geometry. As first I want to use the drive for saving own files.

My idea is to load the bootsector in a free memory area via SIO and save this with the BIOS function (EPROM) to the disk.

Best regards,
Dietmar

Chuck(G)
March 7th, 2012, 11:30 AM
The 1771 controller is soft-sector only--and single-density at that.

I don't understand what you mean by "counter" however.

kleindi
March 7th, 2012, 11:56 AM
Hi,
find attached a part of a schematic for an 8" drive from Siemens, which was able to be used as a hard or soft sectored drive. If you use it as an hard sectored drive you must install a "hard sector option". I read in the manual that this contains a counter so i assume that this counter was used for determining the index whole. But this was wrong. Sorry for this confusion.

The "Hard Sector Options" provides a logic for the index and a counter for using the drive as an 8/16/32 sector per track device.

8156

8155

But overall, i hope that every hard sector drive is usable as a soft sector drive by ignoring the sector signal.

Do you think i'm wrong?

kleindi
March 7th, 2012, 12:48 PM
After reading the datasheet from the 1771 I understand that this item only do FM for SD and the Micropolis 1053-II need MFM for DD.

That will be the reason that this combination will fail.
Am i right?

Chuck(G)
March 7th, 2012, 02:04 PM
find attached a part of a schematic for an 8" drive from Siemens, which was able to be used as a hard or soft sectored drive. If you use it as an hard sectored drive you must install a "hard sector option". I read in the manual that this contains a counter so i assume that this counter was used for determining the index whole. But this was wrong. Sorry for this confusion.

Are you perhaps looking at the Siemens FDD-100 or FDD-200 8" drives? They're great drives for 8-inchers (I use them), but they have jumpers so that sector hole pulses can be separated from index hole and routed to a separate pin. Since all 8" hard sector disks are 33-hole (32 sectors), the Siemens drives also allow diving the sector signal down to form 32, 16 or 8 logical sectors.

On the other hand, if the HS jumper isn't installed on the drive board, it will function as a normal soft-sectored (i.e. "dumb") drive.

This is not relevant to your situation, however. The 1771 does do FM only, but that has no bearing on the media or drive, as the minimum pulse distance is the same on both FM (2 Ásec. and 4 Ásec.) and MFM (2 Ásec. 3 Ásec. and 4 Ásec.). Floppy drives are very, very simple devices.

You could upgrade your controller by using, say, a 2791 and doing a little rewiring, but there would also be software changes.