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smp
May 26th, 2015, 04:57 PM
Hello all,

I am happy to let you know that I finally have my IMSAI system working with a Z80 CPU, a full 64K RAM, a Northstar floppy disk controller, and two 5.25" floppy disk drives.

It's been a bit of a long journey. I am certain that a number of folks here can remember my posts over the past few years, as I tried from time to time to get this IMSAI stable and working. I've been convinced all along that the IMSAI chassis and front panel are good, but the S-100 boards have sometimes seemed stable, and other times seemed glitchy. It's a great pleasure to have things finally pan out.

Back when, I first tried to get up and running with a SD Systems Versafloppy II controller, but I ran into a lot of difficulties. Another time, I tried to get a Northstar floppy disk controller going, and again I ran into difficulties. Recently, I've been posting here and in the CP/M thread about my latest adventures, again with a Versafloppy II.

As I wound my way with my most recent attempt with the Versafloppy II, I found a mis-marked floppy drive cable that had me plugging it in backwards. I recall that the problems I encountered long ago were probably caused by that same cable. On top of that, I also discovered that I had a floating ground (essentially no ground connected) between the power supply and the floppy disk drive. This time with the Versafloppy II, the problem showed up as garbage characters being output to my terminal screen. I believe that this problem also showed up in my earlier try with the Northstar controller. That time, I could read floppy disks, but when I attempted to write to a disk, all I got was garbage.

So, in this most recent round of effort with this system, I achieved success with the Versafloppy II controller working with the VF diagnostic program provided by John Monahan on the www.s100computers.com web site. As I posted elsewhere, my floppy disk drives have trouble initializing disks with 128 bytes per sector, and the software development effort for me to create the code to handle 512 byte sectors for CP/M is a bit of a bridge too far right now.

Buoyed by that success, I dug my Northstar floppy disk controller out again and gave it a go. I assembled the source code for an early version of Northstar DOS, patched it for I/O through my system monitor, loaded it up and did a warm start. Got Northstar DOS running. Had problems, however, with trying to initialize disks. Northstar DOS not really running.

Then, I remembered that during my past attempt with Northstar, Glitch had helped me out and provided two Northstar boot disks, in trade for a few 10 sector hard sector disks. I remember that I ended up destroying one of them, but what about the other?

Well, the short story is that I dug out that master disk that Glitch provided, and I tried a cold boot, and, VOILA. I am up and running with Northstar DOS version 5.1. I've been able to initialize 4 disks, and copy the master disk 4 times, and all of them have no errors, and all of them boot properly.

I am up and running!

Just one more anecdote to complete this story. Long, long ago, I had the very first computer store in New Hampshire, Microcomputers, Inc. While I was in business, I sold IMSAI computer kits and assembled systems, and Northstar floppy disk add-on systems (among other S-100 equipment). One of the systems I sold to a fellow was an IMSAI with a Merlin video graphics interface and a Northstar floppy disk system. That system is the one I have dreamed of owning ever since then. Well, I don't have the Merlin video graphics interface, and I may never will, but I now have the system I have dreamed of for all these years. What a thrill!

Thanks to you all for all the help you have offered me over the years.

Thanks for listening.

smp

JDallas
May 26th, 2015, 05:38 PM
Re: Z80 + NorthStar MDS + Merlin Graphics Display

...One of the systems I sold to a fellow was an IMSAI with a Merlin video graphics interface and a Northstar floppy disk system. That system is the one I have dreamed of owning ever since then. Well, I don't have the Merlin video graphics interface, and I may never will, but I now have the system I have dreamed of for all these years. What a thrill!...

I have a Cromemco Z-2 system that I built and put together starting in 1977. I chose the Miniterm Associates MERLIN display board with the Super Dense Graphics daughter card. MERLIN was great. Used it as the firmware monitor (MBI&MEI) for the system for years, until Miniterm Associates sent out a newletter with a hack for installing it on NorthStar MDS systems. I bought one and modified it (Video DMA conflict) and they worked perfectly together. I used a converted Hitachi B&W TV with a Pickles&Trout kit converter for the display.

I still have these systems (I suspect I bought every piece of hardware Miniterm made) but have to restore them someday.

Don't even ask if I'll ever sell it. :)

One note on the MERLIN: It put out big time radio frequency interference. Neighbors on both sides would tell me about the Ham Radio interference with their TV reception. I mostly tried to run the system after midnight, because... hey... that's how we coded back then... lose track of time and stop when you've finished.

I'm crazy enough to design a retro version of the MERLIN (III) on a S-100 with higher capability. I like the monitor proms they did so would have to keep the Merlin command set (and fun) with the new system. Maybe their Graphics BASIC could be made compatible. I've done a lot of eZ80 designs this year and some are likely to go into retro versions.

If you want a replica, I could do the layout based on the documentation they provided. You'd have to check the parts list to see if that's worth doing.

By the way... I worked for SD Systems circa 1983 and designed their Versa-Floppy-Winchester III (4 floppies + 3 SASI drives). They charged so much for that board I doubt any hobbyist could afford one. At the time SDS was convinced that hobbyists were out and industrial/commercial were the new market... one year later they sold the computer division.

Rumor has it I know where to find a set of mylar gerber prints for it. :)

Sad thing, the day they sold the computer division, we showed up to work and they had taken all our computers with TurboDOS, SBC300, VFWIIIs and rom/ram disks. I haven't seen one since.

I do still have all the chips Western Digital sent me. I pulled the WD chips out recently and some are stamped... "PROTOTYPE" - they were doing the chips in real-time with us. Personally I didn't care for WD's work and wouldn't have used them if I was given complete design freedom.

I also have a bare board VFW-III and I have the prototype version populated. The Prototype was a hand taped version that had issues. The production version was SDS's first CAD layout, done in Atlanta Georgia by the contractor that did DCHayes boards.

snuci
May 26th, 2015, 05:48 PM
Congrats smp. It is seriously rewarding when you can get something like this going.

If you ever want to take another run at the VersaFloppy II, The Zeus 80 I have uses a version of the VersaFloppy II and it boots CP/M 2.2 but it's on 8" floppies. That said, I do have a 5.25" drive that's supposed to work with it (hanging out of the back).

smp
May 27th, 2015, 06:33 AM
I have a Cromemco Z-2 system that I built and put together starting in 1977. I chose the Miniterm Associates MERLIN display board with the Super Dense Graphics daughter card. MERLIN was great. Used it as the firmware monitor (MBI&MEI) for the system for years, until Miniterm Associates sent out a newletter with a hack for installing it on NorthStar MDS systems. I bought one and modified it (Video DMA conflict) and they worked perfectly together. I used a converted Hitachi B&W TV with a Pickles&Trout kit converter for the display.


Thanks very much for sharing all that information about your system, and especially about the Merlin video graphics interface. I vaguely recall the difficulty between the Merlin and the Northstar, but I would not have remembered it if you had not brought it up. I guess it must not have been a big deal since Miniterm brought out the mod for it, but nowadays that might be a show-stopper, because I haven't seen any documentation still around describing it.

The thing for me with all the old S-100 video interfaces is that they use a chunk of the existing memory. Memory resources are thin enough in a 64K total RAM system without giving up a chunk for this and another for that. I'd love to see a reasonable video and graphics board that contains its own RAM for the video output for the S-100 system.



By the way... I worked for SD Systems circa 1983 and designed their Versa-Floppy-Winchester III (4 floppies + 3 SASI drives). They charged so much for that board I doubt any hobbyist could afford one. At the time SDS was convinced that hobbyists were out and industrial/commercial were the new market... one year later they sold the computer division.


I love the Versafloppy II floppy disk controller, especially since I have a fully good and working one. Since I do not have a pair of good working 8" floppy disk drives, nor do I have a pair of sufficiently old floppy disk drives that will format floppy disks with a format that has 128 byte sectors, I am out of luck for pursuing CP/M with my Versafloppy II. I suppose one day I may finally acquire the disk drives that will allow me to give that a try, but for now, taking a look at the effort to do a BIOS with blocking/de-blocking to translate between 512 byte sectors on the floppy disk, and 128 byte sectors that all the support code that CP/M seems to require, is too much for me.

If anyone cares to create a BIOS for CP/M using the Versafloppy II interface to DSDD 5.25" disks using 512 bytes per sector, please let me know. I'd love to get a copy of your code!

smp

smp
May 27th, 2015, 06:40 AM
Congrats smp. It is seriously rewarding when you can get something like this going.

If you ever want to take another run at the VersaFloppy II, The Zeus 80 I have uses a version of the VersaFloppy II and it boots CP/M 2.2 but it's on 8" floppies. That said, I do have a 5.25" drive that's supposed to work with it (hanging out of the back).

Thanks very much for your thoughts.

Yes, the Versafloppy II board can do the older formats requiring 128 bytes per sector, and all the code that's around for both 8" and 5.25" floppies is written for 128 bytes per sector. I just do not have a pair of good working floppy disk drives that will do formatting using 128 bytes per sector reliably. The format gets done, but checking afterwards with the VF diagnostic program doing random track/sector writes & read-backs gives some errors. Not a lot of errors, but it does not go perfectly as when I do a format using 512 bytes per sector. Sigh. If I had the right floppy disk drives, then I might be able to give it a go. Maybe one day I'll get a pair of the right floppy disk drives.

smp

JDallas
May 27th, 2015, 10:17 AM
...The thing for me with all the old S-100 video interfaces is that they use a chunk of the existing memory. Memory resources are thin enough in a 64K total RAM system without giving up a chunk for this and another for that. I'd love to see a reasonable video and graphics board that contains its own RAM for the video output for the S-100 system.

Exactly.

If I did a Merlin-Revisited, it would be an independent controller with its own microprocessor and video ram so it wouldn't hog the S-100 bus. I'm using several 2Mbyte static rams on my 50Mhz eZ80 designs and they can fly through video ram for rendering on its own. I might use a dual bank so the screen writes don't block the rendering; cheap memory gives you new options.

The microprocessor would likely be able to offer additional portals to modern interfaces, thus allowing the S-100 to "get out of the box."

smp
May 27th, 2015, 02:25 PM
If I did a Merlin-Revisited, it would be an independent controller with its own microprocessor and video ram so it wouldn't hog the S-100 bus. I'm using several 2Mbyte static rams on my 50Mhz eZ80 designs and they can fly through video ram for rendering on its own. I might use a dual bank so the screen writes don't block the rendering; cheap memory gives you new options.

The microprocessor would likely be able to offer additional portals to modern interfaces, thus allowing the S-100 to "get out of the box."

That sounds excellent to me. If you were to do this project, you might also contact John Monahan at www.s100computers.com and see if you can get your bare board on the list of boards being offered to the S-100 community that he has there. I would be very interested in getting one, either bare board, or already assembled and tested.

smp

DDS
May 28th, 2015, 04:50 AM
"As I posted elsewhere, my floppy disk drives have trouble initializing disks with 128 bytes per sector, and the software development effort for me to create the code to handle 512 byte sectors for CP/M is a bit of a bridge too far right now."

I've been able to find examples of CP/M sector blocking/deblocking code, one of them being here:

http://www.gaby.de/cpm/manuals/archive/cpm22htm/axg.htm

I'm not clear on whether you want to "roll your own" or just put together something that works. But more than one source code example is out there if your goal is the latter.

JDallas
May 28th, 2015, 05:43 AM
"...software development effort...to handle 512 byte sectors for CP/M...

SD Systems was good about including BIOS listings for their cards. I'll check some manuals tonight to see if there is at least so code that could be easily modified.