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Floppy controller ID

L

litterbox99

Experienced Member
Joined
Aug 8, 2010
Messages
103
I recently picked up another Imsai and it came with an external
floppy drive(s) and controller card. I haven't been able to find
any doc's on the controller; Micro Applications INC. 2100.

http://home.mchsi.com/~litterbox99/temp/floppy.jpg

I'd like to know more about it before I power it up.
I was able to ID the drives, two Shugart 400's.
I don't know if there mini's, they measure about 3" 1/2
tall.

http://home.mchsi.com/~litterbox99/temp/drive.jpg

The drives are clean, but it looks like the power supply
has had a few rectifiers replaced and there is evidence
of burning on the PCB. I have a switcher that is just the
right size I'll drop in.

It came with 14 floppy disks labeled Dos, Basic, Games,
monitor and etc... These disks have more than one index
hole, like 10 of them, so from what I gather, they are hard
sectored ?

Is a Shugart 400 a soft or hard sectored drive ?
or is this controller dependent ?

I'm not sure if the disks & drives are original to the Imsai.

Yeah ! more to learn :)
 
I looked at the eBay listing. It mentions Northstar system software. This is an area where I can help. My IMSAI is a PCS 80/30 with a MPU-B Board (8085 CPU). I used two different disk controllers -- a Northstar MDS (single density) and a MicroComplex Controller (double density). The MicroComplex board is in the system today. I bought my IMSAI (new) in 1977, and I used Northstar DOS mostly in the first year or two. I started with DOS 3.x if my memory serves me, and upgraded to 4.0, 5.0, and 5.1. I wrote a great deal of software which ran under DOS, including a macro based higher level language.

I also used CPM (V1.4 and V2.2) and the UCSD Pascal P-code system with the Northstar Drives. In the past few weeks I have been installing various CP/M 2.2 applications. I have been able to bring up Wordstar/SpellStar and CompuView Vedit, both of which drive the video controller card (VIO-C) in its native (memory mapped) mode of operation. I also have been able to install and run MBasic (interpreter), as well as the BASCOM (compiler) and the Fortran-80 compiler. There is a lot of software available in the Northstar format.

I have a great deal of of documentation (scanned to PDF) on the software I used. When your system is operational, I can provide links.
 
Thanks for the info Ken.

Learning something new every day with this hobby.

Now for some more questions...

Will I be able to 'boot' from any of these disks ?
Or will I have to toggle in a loader? From what I
have been reading, I understand it goes both ways.

The controller looks like it has a bipolar ROM labeled
'boot' Does this prom have the loader or is it stored
like a boot sector on the disk ?

Or do I have to jump to an addy, the seller mentioned
something about he could never get DOS going and
referenced jumping to $E900 with no results...


New blank media.

I did some searching and it doesn't look like you can
buy hard sectored (10) 5 1/4 disks. I did see on another
forum where they talked about making a punch jig. I wouldn't
have a problem with this if I could buy some media to modify.


That should be enough for now ;-)

Todd
 
Hi Todd,

I'll take a shot at answering your questions. First, let me lay out some assumptions. It would appear from what the seller said, and from the list of manuals, that the 14 diskettes contained Northstar DOS and the Northstar Basic interpreter software. My guess is that this was probably an earlier version of DOS, probably single density. I don't know whether the disk drives themselves were manufactured by Northstar, but that is quite possible. Northstar provided their MDS disk system to IMSAI and other S100 manufacturers. I have no knowledge of the controller card, but it could Northstar MDS compatible, as my MicroComplex controller is. The seller said that he was not able to get the disk drives to boot from a floppy, so it is not clear if the hardware is working or not.

Q. Will I be able to boot from any of these disks?
A. All depends on how they were created. A floppy may or may not contain a copy of DOS on the diskette. If it does not, then you would not be able to boot from that particular diskette. It was common practice to put a copy of DOS only on certain diskettes, and those were the ones from which the system was booted. Others might have been used primarily as data storage diskettes. Once DOS was loaded into RAM from a bootable diskette, that diskette could be removed, although it was common practice to keep a bootable diskette in drive 1.

Q. Will I have to toggle in a loader?
A. If the hardware is working, and the diskette(s) contain DOS, you will not have to toggle in a loader. The bootstrap software is contained in ROM on the controller card. Northstar diskettes which were properly initialized (formatted) contained the disk catalog (directory) in sectors 0-3 on the first track. If the diskette contained Dos, it would start in sector 4 on the first track, and would be 10 (single den) or 6 (double den) sectors in length, depending on the version. The bootstrap loader in ROM would read the first sector of Dos into a specified RAM location, usually $2000 and then branch to a given routine which would load the remainder of Dos. A sector contains 256 bytes on a single density diskette, and 512 bytes on a double density diskette.

Q. Do I have to jump to a given address?
A. Yes. On Northstar single density controllers this address was usually $E900.
On double density controllers, the address was usually $E800.
The seller mentioned that a jump to $E900 caused the disk to spin if I remember correctly. That would indicate that it was trying to boot.

Q. Can I still buy 10 sector hard sector diskettes?
A. This has been discussed in previous posts. They are still available from an outfit in Calif. The name escapes me at the moment, but I will look it up. I seem to recall a price of $35 per box of ten. The jig that you mentioned was made available to forum members by Dwight Elvey. I bought one and it works pretty well. Contact Dwight to see if he still has any for sale. This jig requires 360KB (soft sector) media.

Ken

Edit: The supplier of 10 sector (hard sector) diskettes is Athana.
 
Last edited:
Thanks Ken ! something to digest...

It's funny you mentioned $2000, this system is configured
for memory starting at $2000-$9FFF with various memory boards.

Looks very promising :)


I never did understand why some S-100 systems with DOS or
CPM start at an odd addresses above 00h. In my mind, I would think
you would start at 00h and work your way up.

Thanks

Todd
 
Hi
The drives don't know hard from soft sectored.
The controller determines hard/softsectored.
400's are FM drives and single sided.
Dwight
 
litterbox99 said:
Thanks Ken ! something to digest...

It's funny you mentioned $2000, this system is configured
for memory starting at $2000-$9FFF with various memory boards.

Looks very promising :)


I never did understand why some S-100 systems with DOS or
CPM start at an odd addresses above 00h. In my mind, I would think
you would start at 00h and work your way up.

Thanks

Todd
Click to expand...

Hi
If the system has no way to swap out the ROM on boot,
it can't have RAM at zero.
This was not all that uncommon for systems other than CP/M
to have RAM starting at something other than 0.
CP/M wouldn't have started with RAM at 0 if it hadn't
been developed on a Intel developement system that
had the ability to swap the ROM out. While you see it
as a flaw of the other systems, I see it as a flaw in
CP/M.
Dwight
 
Dwight Elvey said:
Hi
If the system has no way to swap out the ROM on boot,
it can't have RAM at zero.
This was not all that uncommon for systems other than CP/M
to have RAM starting at something other than 0.
CP/M wouldn't have started with RAM at 0 if it hadn't
been developed on a Intel developement system that
had the ability to swap the ROM out. While you see it
as a flaw of the other systems, I see it as a flaw in
CP/M.
Dwight
Click to expand...

All very true. By the time that IMSAI developed the MPU-B board, which I use, they provided an option in the Monitor program to disable the (ROM at $0000/on-board RAM/system timers) before jumping to the bootstrap loader in ROM on the disk controller board.

The CPU-B was sort of strange in that the monitor ROM which appears at $0000 also appears at $D800, and it is tied to the timers which I have to enable momemtarily in order to program the baud rate on the 8251 UART. They only exist in address space for a few instructions, after which they are disabled -- but this caused me some problems when I was bringing up a 56K version of CP/M 2.2. The monitor ROM at $D800 and my code in CBIOS collided with each other while I was setting up a timer. Had to drop back to a 55K system to avoid the conflict.
 
Last edited:
litterbox99 said:
Looks very promising :)
Todd
Click to expand...

Let's hope so -- but there are still some issues to resolve. I was going to mention this in my previous post, but it was getting pretty long and I decided not to muddy up the waters.

The diskettes you have, and which we assume contain N* DOS, are configured for some sort of console. Without a working console, DOS cannot talk to you; and without a working DOS, it is difficult to configure the console. Unless I missed something, your system did not come with a console (usually some sort of CRT terminal connected to a serial port). My IMSAI, on the other hand, uses an intelligent keyboard connected to a parallel port, and a monitor connected directly to the video card to provide the system console. Unlike many "off the shelf systems" which were to follow, the IMSAI usually did not come with a console.

The system console must be implemented in the BIOS portion of DOS. There are four jump vectors in DOS which point to routines in the customized BIOS, specifically:

at $200D -- a jump to your character out routine (could be as little as 6 instructions)
at $2010 -- a jump to your character input routine (could be as little as 6 instructions)
at $2013 -- a jump to the routine to initialize your terminal, if required, or a simple return
at $2016 -- a jump to the routine to handle a control-C abort

These routines are located in an area which DOS provides at $2900. Your DOS manual covers all of this and has a sample BIOS. This is not complicated, but may be a little intimidating the first time you have to do it. CP/M and UCSD P-Code systems require that a similar BIOS be provided.

Those great looking toggle switches, and those blinking lights on the front panel are sure nice to look at, but to do some useful work you must have a console of some sort or another. If your DOS was configured for a terminal on the serial port, and you have such a terminal, then what you have may work.

Ken
a photo of my old IMSAI
http://home.comcast.net/~kvaughn65c/imsai_pcs_80_30.jpg
 
Last edited:
Ken, Dwight,

This is great information you guys have provided !

I have another Imsai with a serial IO that I have been able to
toggle in a short program and send/receive chars to my PC
running Tera Term. So for the most part I have a console.

What I plan to do this weekend is to get the new Imsai up and
running with everything but the floppy drives. Once I have confirmed
the serial works, then I'll experiment with the floppy controller & disks.

Todd
 
litterbox99 said:
I have another Imsai with a serial IO that I have been able to
toggle in a short program and send/receive chars to my PC
running Tera Term. So for the most part I have a console.

What I plan to do this weekend is to get the new Imsai up and
running with everything but the floppy drives. Once I have confirmed
the serial works, then I'll experiment with the floppy controller & disks.

Todd
Click to expand...

Sounds like a good plan.
 
Well here's what I've done so far;

I toggled in a program to echo chars
to TeraTerm from the keyboard, this works.

I replaced the drive power supply with a switcher,
examined the controller card and mechanics on
the drive(s) and looked at the heads under magnification.
All looks good, the drives are very clean.

I attempted to boot my Imsai with all the disks that came
with, I tried both drives. When I jump to $E900, the drive
spins up, the load clap engages and the activity LED is lit.
The drive spins for a while and then stops, nothing on the
console :-( I examined the $2000 range and it looks like
nothing was wrote to memory.

After studying the drive schematics it looks like pin 30 is
read data out to the ribbon cable. I repeated the boot
procedure on all the disks again, but this time I watched
data out with my logic probe.

On most disks I get nothing... the activity LED comes on,
drive spins and the probe indicates a low. Now on a few
disks I do get a pulse train :) but these disks are labeled
as data or application disks. The disks that are labeled
DOS, Basic etc I get no pulse train :-(

I'm going to make an assumption that the disks with no pulse
trains are blank or faded. Maybe the original owner degaussed
his disks before he sold it, after all they did contain data for
his business. I suppose I could break out the scope and
look at the analog signal from the head amp... but not tonight.

Now if someone had the ability to read these disks (hard sectored
10 hole) and verify the contents or if they have the means to
create me a few disks with N* Dos & Basic so I can get somewhere
with this unit, I would be willing to compensate.

I have been doing some research about disk images and such and
everything points to Dave Dunfield and some of his software, but it
looks like he's pulled this off the web. Has anyone used his stuff
or mirrored his site before he pulled his apps ?
 
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