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View Full Version : IMSAI 8080 CP/M 2.2 - Tablet Bluetooth Interfaced



tma
March 8th, 2016, 06:13 PM
Greetings to All in this forum,

I bought my Imsai 8080 in 1979 (as I recall). It had 16KB of ram (4 x 4K static RAM S100 boards). I first used paper tape for non-volatile storage. I remember manually entering the bootstrap via the front panel keys. Once the bootstrap was keyed in and running I used to get a kick out of watching it load 8K BASIC from paper tape. I then progressed to wire wrapping my own cassette interface which was based on the Tarbell design that was popular at the time. Cassette storage was sure an amazing step up in convenience. Finally a year or two later I managed to purchase a couple of Memorex 8" floppy drives and a 64KB dynamic RAM board. Eventually I managed to get CP/M 1.4 up and running after struggling with some board incompatibility issues. In time I ended up with my own customized install of 59.5K CP/M 2.2. I gained some application software memory space by placing the BIOS in EPROM which resides within the 60-64K address space of the memory map. I also ended up with an extender board and EPROM programmer board which were necessary tools. I am delighted to report my IMSAI system still boots up. I recently built a new enclosure for the Memorex drives which includes a converted surplus PC power supply for powering the drives. A couple of years ago I became interested in Android tablet BlueTooth control and decided to build an interface for my Imsai which permits me to use a modern day tablet for the console. For those that might be interested I have posted a photo album here:

https://goo.gl/photos/1MuxrsABEzUvbhnV7

As I am getting long in the tooth I am facing the need to downsize in the not too distant future. Consequently I am going to have to part with my labor-of-love Imsai, :(. I still need to inventory it all to document in more detail what is included so I am not quite ready to sell it yet. But it is time for me to learn about how and where to list it. I suppose eBay is one method but I wonder if there are other possibilities. I wonder if anyone here has any suggestions and if anyone can give me an idea of the market price for a working Imsai CP/M system with about 6 dozen - 8" diskettes loaded with goodies, documentation, a couple of extra boards and a couple of extra drives?

Thanks in advance for any helpful pointers!

Best Regards,
TMA

MicrocomputerSolutions
March 8th, 2016, 06:34 PM
You've developed a great looking machine there!

I'm not really an Imsai person (while I did have one at one time).

But, I'd still guess that you would be looking at a minimum of $3500-$5000 for everything.

That a nice look drive enclosure you built. Is it stable with the drive pulled out like in the photo, does it get tippy?

Is that a pair of Qume DT242/YE DATA 180 1/2 height 8" drives in the picture? Are you planning on replacing the Memorex drives with them?

I think you would probably maximize the sale price if you advertising on eBay, but putting out feelers here would not hurt.

tma
March 8th, 2016, 09:22 PM
Greetings,

Thank you for your prompt reply and information!

Yes the drive enclosure and drive are stable when pulled all the way out for the following reasons:

- The enclosure is heavy, made from 1/8" thick aluminum. I happened to acquire a surplus aluminum ramp which I used for the material. It is heavy enough to remain stable with the drive fully extended. The power supply at the rear also adds a bit more weight but the stability is mainly from the weight of the enclosure.

- Of course when sliding the drive out it is important not to pull it out too far. The rails are marked but there is nothing to stop one from pulling it all the way out. When the marked, fully extended position is reached it is extremely important to immediately lock the 1/2" square solid aluminum sliders with the 1/4" nylon bolts. The thumb screw head nylon bolts are shown in the separate photo where the drive is shown half extended. Once locked in extended position it would be possible with lots of bench space to very carefully tilt the enclosure on its side to gain access to the option jumpers on the underneath side of the drive chassis. The only down side I have noticed to this concept is that when sliding the drive back in one must be careful to guide the cables so that they fold up without catching anything. There is extra space provided for the cables at the back and it is quite easy to reach through the back to guide the cables. A flashlight should be used to keep an eye on the cables during the process.

The Qume drives are labelled QumeTrak 242, serial numbers 024808 and 051907. I didn't notice a /YE suffix. They are half height, double sided, double density drives according to the service manual. I have had them connected and they are functional but I noticed an inconsistency. I encountered one diskette that one of the drives could read and the other reported read errors. However they both worked with some other diskettes. I wonder if there is a slight tracking error. The diskettes I used for testing were written with the Memorex drives. The Memorex drives are heavy duty work horses which seem to be quite consistent so I decided to stick with them. The floppy diskettes have just been kept on a shelf over the decades thus I wonder if the magnetism has deteriorated.

I acquired the Qume drives about two decades ago with the intent of upgrading to DSDD but I never tracked down a DSDD controller card to make it happen. My controller card is an SD Systems Versa Floppy which is a single density controller. I think the Qume drives could be quite easily mounted within the enclosure I made as the widths are very similar. New front trim plates would need to be made up for appearances.

Thanks again for your interest.

TMA



You've developed a great looking machine there!

I'm not really an Imsai person (while I did have one at one time).

But, I'd still guess that you would be looking at a minimum of $3500-$5000 for everything.

That a nice look drive enclosure you built. Is it stable with the drive pulled out like in the photo, does it get tippy?

Is that a pair of Qume DT242/YE DATA 180 1/2 height 8" drives in the picture? Are you planning on replacing the Memorex drives with them?

I think you would probably maximize the sale price if you advertising on eBay, but putting out feelers here would not hurt.

MicrocomputerSolutions
March 8th, 2016, 10:54 PM
YE Data is the company who manufactured floppy drives in Japan for Qume. drives were marketed under the Qume name in some Countries, and under the YE Data name in other Countries.

I haven't ever gotten my hands on a working Qume DT-242. The only one I've ever gotten came from the buyout (by my Company) of another former Compupro's inventory (the 242 did not come from Compupro, and was never supplied by Compupro. It came in a Original Qume Shipping box with one serial number on the box, a different number on the drive chassis, and a third number on the logic board. It's no wonder that it never worked, it was probably used for parts by the other Company. As it sits right now, the logic board is bad, and I can't tell about the condition of the head assembly.

When you were trying to get the 242s working on your Imsai, was that single sided or double-sided? Does the Versafloppy support double-sided drives? I know it only works single-density. Did you try the 242s both single-sided and double-sided? If so, did they work single-sided?

Qume had a problem with the gray color plastic that they used to make the head assemblies. The plastic is age unstable and as a result, the head alignment moves off, with the upper and lower heads moving in opposite directions, making it impossible the get proper double-sided head alignment. Hopefully the black plastic used to make the 242 head assemblies does not suffer from the same problem.

Have you considered getting a Versafloppy II board? They show up on eBay regularly for between $50-$100.

A standard 8" rack mount drive is 4.62" . The 242 is a half height drive, meaning it 2.3". If your Memorex are standard size, they should be 4.62". Two 242s should take up the same front panel space as one standard size drive (drive depth is not standardized, so we see all kinds of depth dimensions on 8" full and 1/2 height drives).

ef1j91
March 9th, 2016, 01:48 AM
Love it! Thanks for posting the pics. It's a beautiful machine, and I love mashups between old and new. I've had a lot of fun interfacing raspberry pis with early-80's micros... mostly Apple II's and Osbornes.

I think there's tremendous value in machines with a provenance like this one, well beyond the "found in scrap / estate sale" machines that frequent eBay. I'm guessing you've got more than a few inquiring messages.

I'm curious where you bought the IMSAI (mail-order? local store?), why that machine over others at the time, and what purposes you had in mind?

tma
March 9th, 2016, 10:50 AM
Greetings,

I have added 9 more photos to the album, mostly regarding the Qume drives. Judging by the difference in serial numbers (024808/051907) it is apparent that the two Qume drives were probably quite aways apart during the manufacturing cycles. Upon closer inspection there is a very noticeable technology difference. One of the PC boards on the earlier unit has many discrete transistors whilst the newer unit uses more ICs. It is somewhat ironic that the older drive is the unit I concluded worked the best. The SN for the main logic board matches the unit serial number of 024808 on the older unit. However as that SN is just on a removable label there may be a different number on the board under the label. The PCB serial number on the newer board is stamped directly into the fiberglass substrate but it does not match 051907. Both units appear to have the same main logic board. It appears the plastic for the head assembly mounts is black for both units which I gather is a good thing.

I must admit I didn't really get into properly testing out the Qume drives. My Versa Floppy controller was not DSDD capable, according to the Qume service manual I needed a calibration diskette for checking the tracking and I needed lots of time to play. Unfortunately I did not have any of the above. My main library of diskettes are just single sided, single density. The Qume drives came with a batch of diskettes loaded with CP/M User Group software. They might be DSDD, but I don't remember trying them. Additionally I was not sure about the option settings and felt the need to look into that aspect further. I am including the Qume drives just in case the next owner wishes to pick up where I left off to quadruple the mass storage capacity.

I imagine there would be room for four of these half height Qume drives within my enclosure if someone wanted to take the time to install additional tracks and cables. The Qume drives are simpler to hook up than the Memorex drives as they do not require 115VAC for the motors nor, as I recall, the negative 5VDC power. The DC power connectors are compatible thus I found it quite easy to get them running.

TMA



YE Data is the company who manufactured floppy drives in Japan for Qume. drives were marketed under the Qume name in some Countries, and under the YE Data name in other Countries.

I haven't ever gotten my hands on a working Qume DT-242. The only one I've ever gotten came from the buyout (by my Company) of another former Compupro's inventory (the 242 did not come from Compupro, and was never supplied by Compupro. It came in a Original Qume Shipping box with one serial number on the box, a different number on the drive chassis, and a third number on the logic board. It's no wonder that it never worked, it was probably used for parts by the other Company. As it sits right now, the logic board is bad, and I can't tell about the condition of the head assembly.

When you were trying to get the 242s working on your Imsai, was that single sided or double-sided? Does the Versafloppy support double-sided drives? I know it only works single-density. Did you try the 242s both single-sided and double-sided? If so, did they work single-sided?

Qume had a problem with the gray color plastic that they used to make the head assemblies. The plastic is age unstable and as a result, the head alignment moves off, with the upper and lower heads moving in opposite directions, making it impossible the get proper double-sided head alignment. Hopefully the black plastic used to make the 242 head assemblies does not suffer from the same problem.

Have you considered getting a Versafloppy II board? They show up on eBay regularly for between $50-$100.

A standard 8" rack mount drive is 4.62" . The 242 is a half height drive, meaning it 2.3". If your Memorex are standard size, they should be 4.62". Two 242s should take up the same front panel space as one standard size drive (drive depth is not standardized, so we see all kinds of depth dimensions on 8" full and 1/2 height drives).

tma
March 9th, 2016, 11:10 AM
Greetings,

I have always been interested in electronics ever since my pre-teen years. Back in the late 70s I wanted to experiment with microcontrollers and I liked Intel products. At the time I was working in an engineering job with a telecommunications company. A friend of mine was really into Imsai and moonlighted as an Imsai dealer. He introduced me to the Imsai 8080. As I wanted to use it as a learning tool the Imsai front panel that displayed the buses and control lines along with the single step control really appealed to me. The S100 buss looked to me like a well thought out design very suitable for expansion. I was looking forward to building some customized boards for an amateur radio teletype (RTTY) application. The Imsai served me well for RTTY. For peripherals I had a VuCom terminal modified for 9600 baud and an RS-232 interfaced GE Terminnet 1200 Baud printer.

TMA






Love it! Thanks for posting the pics. It's a beautiful machine, and I love mashups between old and new. I've had a lot of fun interfacing raspberry pis with early-80's micros... mostly Apple II's and Osbornes.

I think there's tremendous value in machines with a provenance like this one, well beyond the "found in scrap / estate sale" machines that frequent eBay. I'm guessing you've got more than a few inquiring messages.

I'm curious where you bought the IMSAI (mail-order? local store?), why that machine over others at the time, and what purposes you had in mind?

tma
March 9th, 2016, 06:08 PM
Greetings,

It seems as if my previous replies have been delayed by the spam filter - hopefully they we appear here without becoming lost.

I have learned how to add information captions to photos in Google's album service where I have posted my Imsai pictures. To read the captions one needs to click on the photo to blow it up full screen then click on the little "i" icon in the top right corner. This brings up the information side window where descriptive text can be stored. To navigate between photos one just needs to click on the arrow buttons which navigate to the next photo with the info window already open.

Some of the captions I have entered are very short and others rather lengthy. The link has not changed:

https://goo.gl/photos/1MuxrsABEzUvbhnV7

Best Regards,
TMA

tma
March 9th, 2016, 08:46 PM
Greetings,

This may become duplicate as I am trying to repost. It seems as if my previous replies have been devoured by the spam filter. If this gets posted I will send my previous replies again.

I have learned how to add information captions to photos in Google's album service where I have posted my Imsai pictures. To read the captions one needs to click on the photo to blow it up full screen then click on the little "i" icon in the top right corner. This brings up the information side window where descriptive text can be stored. To navigate between photos one just needs to click on the arrow buttons which navigate to the next photo with the info window already open.

Some of the captions I have entered are very short and others rather lengthy. The link has not changed:

https://goo.gl/photos/1MuxrsABEzUvbhnV7

Best Regards,
TMA

tma
March 9th, 2016, 09:40 PM
Greetings,

I replied earlier but for some reason my post must have become captured by the spam filter. It seems to be working OK now.

I have added 8 more photos of the Qume drives to the album. The main PC board of my earlier unit ( SN 024808 ) matches the serial number on the body. However the number is on a label that might be covering up the embedded SN on the PC board. The main PCB of my later unit ( SN 051907 ) has the number embedded in the PCB fiberglass and it does not match the body number. It is evident that these units, which have quite a spread in serial numbers, are from different manufacturing runs as the small PCB on the older unit uses more discrete components. Ironically I think the earlier unit performed the best of the two. It appears the plastic used in the head assemblies is black for both units which hopefully is more stable than the gray problematic versions.

I did not thoroughly check out the Qume drives. To properly determine what was causing the inconsistency I needed a DSDD controller and a tracking calibration diskette which I didn't have. I only tested with single sided/single density diskettes. I am including the extra Qume drives for the next owner who may wish to pick up where I left off. Since the Qume drives are half height I think there would be room for mounting four of them in the enclosure if someone wished to spend the time to add more tracks and cables. The Qume drives are relatively easy to hook up as they only require two DC voltages compared to 3 DC voltages plus 115VAC for the Memorex drives. They are also plug compatible thus the existing cable harness works for either Memorex or Qume.

Thanks again for your interest and helpful information!

Best Regards,
TMA


YE Data is the company who manufactured floppy drives in Japan for Qume. drives were marketed under the Qume name in some Countries, and under the YE Data name in other Countries.

I haven't ever gotten my hands on a working Qume DT-242. The only one I've ever gotten came from the buyout (by my Company) of another former Compupro's inventory (the 242 did not come from Compupro, and was never supplied by Compupro. It came in a Original Qume Shipping box with one serial number on the box, a different number on the drive chassis, and a third number on the logic board. It's no wonder that it never worked, it was probably used for parts by the other Company. As it sits right now, the logic board is bad, and I can't tell about the condition of the head assembly.

When you were trying to get the 242s working on your Imsai, was that single sided or double-sided? Does the Versafloppy support double-sided drives? I know it only works single-density. Did you try the 242s both single-sided and double-sided? If so, did they work single-sided?

Qume had a problem with the gray color plastic that they used to make the head assemblies. The plastic is age unstable and as a result, the head alignment moves off, with the upper and lower heads moving in opposite directions, making it impossible the get proper double-sided head alignment. Hopefully the black plastic used to make the 242 head assemblies does not suffer from the same problem.

Have you considered getting a Versafloppy II board? They show up on eBay regularly for between $50-$100.

A standard 8" rack mount drive is 4.62" . The 242 is a half height drive, meaning it 2.3". If your Memorex are standard size, they should be 4.62". Two 242s should take up the same front panel space as one standard size drive (drive depth is not standardized, so we see all kinds of depth dimensions on 8" full and 1/2 height drives).

tma
March 9th, 2016, 10:10 PM
Greetings,

Thanks for your nice comments! I tried to reply earlier but my post became captured I presume by the spam filter.

A friend of mine who was a IMSAI enthusiast introduced me to the product. He was moonlighting as an IMSAI dealer thus I bought from him. I have been interested in electronics since my pre-teen days and wanted to learn about microcontroller technology. At the time I was working in engineering for a telecommunications company. The IMSAI with its robust front panel that displayed the buses and control lines and that also permitted one to single step through the code seemed ideal for someone learning the ropes. The S100 bus design appealed to me from an expansion viewpoint. I wanted to do some prototype work. For fun I used the IMSAI for amateur radio teletype (RTTY) with it connected to a 300 Baud VuCom terminal which I modified for 9600 Baud operation. I had a 300 Baud ASCII printer with an RS232 interface for producing hard copy. I learned how to write and debug assembler language programs with it and also found it useful for word processing.

The IMSAI provided me a solid foundation for playing with modern day microcontrollers. Sure never sorry I bought it!

Best Regards,
TMA






Love it! Thanks for posting the pics. It's a beautiful machine, and I love mashups between old and new. I've had a lot of fun interfacing raspberry pis with early-80's micros... mostly Apple II's and Osbornes.

I think there's tremendous value in machines with a provenance like this one, well beyond the "found in scrap / estate sale" machines that frequent eBay. I'm guessing you've got more than a few inquiring messages.

I'm curious where you bought the IMSAI (mail-order? local store?), why that machine over others at the time, and what purposes you had in mind?

Tor
March 10th, 2016, 11:43 PM
That's an incredibly nice-looking system. And well integrated. When I think of my own chaos.. a couple of 8" drives in one box, random bits and pieces of a system here and there..

tma
March 11th, 2016, 05:27 PM
Thank you so much for your kind words! I understand the situation well. I needed a decent enclosure for the drives for a long time before I finally found the labor intensive time to make one, (:/)).


That's an incredibly nice-looking system. And well integrated. When I think of my own chaos.. a couple of 8" drives in one box, random bits and pieces of a system here and there..

Rick Ethridge
March 11th, 2016, 06:30 PM
Very, very nice! Polished and professional.

tma
March 11th, 2016, 09:40 PM
Greetings Rick,

Thank you for your kind words!!! This computer is one of those pride and joy material things, (:/).

Best Regards,
tma




Very, very nice! Polished and professional.

tma
March 11th, 2016, 09:42 PM
Greetings All,

For anyone that may wish to know I have put together a contents list for the documentation package which can be found here:

https://drive.google.com/file/d/0B2k_ZSjGm_jnU2tRaWRGMGRRX0E/view

Thanks for your interest!
tma