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IMSAI PCS-80/35 or maybe an IMSAI 4x

Tried a write tonight, but got an error 94, CRC error in the ID field.
This will take a bit of investigation.
I don't have true SSSD disks so I was trying to format SSDD as SSSD.
Maybe you can get a laugh about this and pass on a hint.
The format seemed to go OK
I had tried to read track 2 sector 3 from my formatted disk and I was getting NOT READY from monitor.
I was convinced monitor was not detecting my 8" drive and sending the command to the 5.25" disk command address.
The IMSAI DIO has two different entry points for commands one for 5.25 and one for 8" drives.
I could see the correct disk command in disk buffer 0, 0x0080.
Now I am thinking that there is some issue with the format....
Time to get the scope out.
I got my 75188 serial translator today, but the system seemed to be working OK, so I didn't take the time to swap it out.
I'll leave it up tonight and make sure the serial output goes in the tank.
I am actually getting younger as I work on this.
In my last post I said I would reply the next day, which I did, but the time says 2 days have passed.
I hope you see the benefits of posting on this forum.
My white paper will be out in August on means to to slow aging.
Al
 
My serial port began acting weird again so the MPU-B came out.
I swapped out U40 with a new TI 75188 thanks to the eeebay.
Still running to see if I fixed it or I have to go to the mountain of contemplation.
I went with my son today and managed to get some 8" SSSD disks from my donor organization.
These were used, but am giving them a try.
We used a bulk eraser to hopefully clean up the disks.
I have two 8" drives, but I think I am seeing read data coming from one of them when the head is not loaded.
SA800 TP 16 was what I was looking at.
This is the drive I have been using up until now.
I moved over to the other drive and have formatted two of the SSSD disks I got.
I start my write routine to write 0x1000 bytes, or 0x20 sectors.
The write stopped at sector 0x0B (maybe actually 0x0A; need to look at my code) with an error code of 0x94, CRC error in the ID sector.
The ID sector is "overhead" (not useful data to the user) of any disk record and contains the track, sector and head info and is CRC protected; lets the drive know if it is in "Kansas" (right place) or not.
I will try another disk tomorrow.
Serial port is still hanging in there.
...
I think you should listen to this (tonight as it is):
Al
 
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Well the serial port "seems" to be hanging in there.
I will not power down the IMSAI chassis and keep dumping memory (such as d 3000,3FFF for monitor commands) for a few days until I can say the serial port is solid.
Fingers crossed I don't have to deal with this again.
As a side note I have been changing Teraterm serial port settings to 50ms for transmit delay.
I was at 200ms, and 50ms seems to be working and I feel about 4x better ;).
It was taking quite a bit of time to load the partial data image I was trying to write (0x1000 bytes / 0x20 sectors of data).
The speed up has helped.
At some time I want to find out just how fast I can throw characters at the MPU-B before it starts dropping characters.
I don't think this is the time (until I reach some sort of stability).
So as a bad scientist I repeated my write to my disk described above and again tonight and it stopped at sector 0x0A or 0x0B (I think 0x0A) with the 0x94 error again.
I hope i don't have to to describe bad science, I think I just described it.
Well, I've got a big batch (10) used SSSD disks (thanks G33ksquadmn), so I thought tonight would be dedicated to formatting these (actually 9 disks, the one with the issue was formatted).
Format / write time is for an 8" SSSD Shugart drive ~ 12.6 seconds per sector, so to format the disk it is just over 16 minutes.
I'll format all of these and see if I keep stopping at the same sector in my code
This will hopefully delineate if I have a bad drive or a bunch of disks that will not write past track 0 sector A.
BTW - My code seems to have worked for the 5.25 disks, never stopping until the write area had been written to the disk.
I have been editing my code and adding more comments to allow formatting and writing with the IMASI DIO-C and just running from the monitor.
I will review and send an update in the next day or so.
In my code I only have 0x1000 / 0x20 sectors of space at 0x2000 to 0x2FFF; I need to make an updated version to relocate the code to 0x2000
and the write data area to 0x3000 to 0x7FFF, or 0x4000 to 0x7FFF to make it a bit more usable.
Something for my free time.
I really like the Beach Boys song I left last night; my wife said it was too melancholy.
Thoughts?
I'll pick it up a bit with the next song - CB - Guess who is this.
Al
 
Well I formatted my 9 other disks; I don't know if IMSAI monitor does any other validation.
I'm beginning to think not, just write.
With my 10 disks I have tried about 4 or so with varied results.
With some I wrote a few tracks, some none.
With some I have had slightly better success on inner tacks.
Sorry, but I have fallen into a bit of bad science; poor data collection.
I was just whipping through 4 or 5 disks and seeing what they would do.
I got into a bit of a rhythm trying to write tracks 0, 0x20, 0x40, and then like 0x48.
Almost similar results.
I swear I was getting 6, 8 maybe a few more to write before I was getting the 0x94, index not found issue.
Now I am only getting 1 or 2 before the 0x94 shows up.
This is getting me to think:
A. Look at the write data on a format and see if it looks OK
B. Go back to drive 1 and see what I am getting out of it; I thought I was getting read data pulses on the SA800 with the carriage open.
C. Suspect something on the DIO where the SA400 / SA800 data converges.
I think this the right order.
A small ray of optimism; serial port has been rock solid for a few days continually powered up.
The U40 replacement seems to have been the trick.
I found a nifty iphone app that lets me check the drive speed - I'll insert below.
It doesn't tell you the speed, but you adjust it until your moving object stops moving.
My drive 2 speed is within spec.
Well, my hint was CB for a song.
Maybe you have guessed the artist.
I have asked my dear son and and numerous colleagues opinion; none responded.
I clearly have bad taste in music.
Deal with it ;)
Speed shot:
SA800-2-Speed.JPG
Courtney:
 
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So I went through all of my 8" SSSD disks on my drive.
All were either stalling on track 1 or 2 (this is 1 based indexing for track number).
All reported 0x94 error, error in the index field CRC.
This 8" drive may take some work.
Not sure if it is my DIO card or the drive.
I never really discussed the DIO card I have; maybe I am still not sure.
DIO cards seemed to have existed in (at least) a DIO-A (maybe just DIO) DIO-B, DIO-C, and DIO-D.
From the "MDIO-disk_sys_ref_manual.pdf" page 34:
DIO-A (1st DIO version I believe) supported, 2 formats, Format 1, an IBM 3470 SD format (not sure if it supported SSSD and DSSD) and a format V a 128 byte DD format for standard drives only.
DIO-B seemed to be a 1 off that supported CalComp 142 (I have no idea what I am writing here) with a different (sector) step rate.
DIO-C SD and DD on 8" drives
DIO-D SD and DD on 5.25" drives.
I think there is one more, maybe a super variant, out there.
I'm pretty sure I have a DIO-A.
The strange thing is I thought I saw an image of a DIO-D with both the 32 and 50 pin drive connectors installed, but the 50 pin had a blank connector installed.....
...
Because I believe I have the DIO (DIO-A) I should be able to support both 5.25 and 8" SSSD drives.
Why the heck can't I format, write and read my 8"-ers.
...
Regression testing....
I yanked the 8" drive tonight and went back to the 5.25 drive.
I read the disk I had formatted and written in the drive 1 (1 indexed) location and repeated the read with drive 2.
Both drive read what I wrote just fine.
The DIO (and PDS - P?? Data Separator; separates the FM clock from the FM data) seems to be working fine for the 5.25 drives.
I am going to look at the data stream on the 5.25 tomorrow or the next and get timing.
I'll post the bit frame timing of the 0s and 1s and maybe an example of 0s and 1s being read from the disk on the 5.25.
Then back to the 8" for comparison.
...
After numerous appeals to US domestic folks on last night's song, without response, I am certain I am getting ghosted.
I'm getting use to it.
Love Al
 
Here is a data stream from the 5.25 disk measuring on the SA400 TP6.
It is listed as +data , it really looks like -data.
I inverted my channel for the capture.
The disk is formatted (FM encoding) and the format data is 0xE5
The first clock of the FM data starts at the not edge of the scope trace, but the next (second vertical graticule)
Starting there you will see the first rising clock edge followed by the next rising edge that is the "1" data.
Follow this pattern further and you will see two more instances of this followed by a clock edge, but no data in the expected time.
This is the first "0" zero of the 0xE5 data - clock "1" clock "1" clock "1" clock "0", 0xE.
The balance of the trace shows and additional 0 1 0 1 with the clock pulses in between if you get the pattern.
This byte happens to the the first bit of the sector.
What precedes it is is the AM byte that tells the system if the sector is "live data" or "deleted data" - 0xFB or 0xF8 respectively.
This trace only shows the first 0xE5 of the data in the sector.
I think there is something different in the architecture of the clocking of the AM field; I think missing clock pulses for maybe bytes 3-5;
it escapes me now.
I need to go back and read more; I could be messing up FM and MFM recording.
Who in the world is looking at this bologna anyway?
I am going on a little time off, just a few days.
I was thinking of taking the IMSAI, but I realized I wouldn't have AC power ;)
Maybe time for reflection.
Enjoy your week.
Maybe enjoy this song below the screen of the 0"s and 1"s; a little music lession
Al
5.25-Format-Data-Read-E5.JPG
 
Well my hiatus does not seem to be noticed; I'll get back to my IMSAI toils as time permits.
Had a nice trip to the Porkys in MI.
Good hikes, nice times with friends.
Throw in a funeral, work and bad bearings on the pontoon trailer, a fishing trip to Leach lake, and poof, time fly's.
Now the only obstacle is the MN State Fair, and a cabin trip or two.
Promise to get back to this stuff as soon as my free time expands as a function of other life interference's and pleasures.
Why work on computers when you can hike here in MI:
Porkys.JPG
 
My MPU-B I flashed to version Monitor 1.3 on a 2716. I think the code executed at D83CH initializes the serial port for terminals. My version makes the mode byte AEH at that point. If I read it right that designates ASYNC, 9600 baud, 8-bit, no Parity, 1.5 stop bits. I don't know how to get some terminal programs to recognize 1.5 stop bits :). Anyone know what works best under Linux for a terminal program and a MPU-B? If 1.5 stop bits is correct you entering 1 or 2 stop bits might cause things to be a bit out of wack. If i'm figuring wrong someone please correct me.
 
I may be being foolish using AEH. This is not 1978. What works best with modern PCs and this old hardware? Forgive me Albert if I am stepping on your thread. I only used AEH as that was the original mode byte. Perhaps we should change it?
 
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Got my MPU-B to initialize a serial connection to a terminal on J3. 8N1 works for me without problems. For me installing a rejuvenated SD ExpandoRAM 64 memory card was enough. MPU-B: S1-3 and S1-8 ON, S2-2 ON. All others OFF. Now I will be able to use the Monitor to drive a Cromemco 8K ByteSaver to program some 2708s for my VIO-D's character set :). The VIO-D mostly works with only U49 populated.

How are you going with the drives? Getting my DIO/PDS working with a PerSci 277 is my next hurdle. The "B" command :)!
 
I like all the music videos you posted, you will probably like this one too:


(and if you really like Hey Joe, check out Slash's version of it, it would have made Mr. Jimi very happy)
 
Well - That was a nice way to entertain people, almost like one of those elaborate domino tumble things - thanks!
.
Sorry - Absent due to other interests and I have released the IMSAI back to the cloud (OK, original holders).
I violated my no activity within 366 days (the most lenient lenders allowed me the extra day as a possible leap year day).
Joking - I gave it up physically about a month ago, I was a bit wrapped up and thought someone could push it on a bit more.
Now I am missing it a bit... especially since someone responded to this thread - thanks Fritz for waking my brain and Hugo waking whatever music wakes up (soul, sole, ...).
.
For Fritz, you got past the serial port issue, but I always struggled and used an old PC with 9600 8-0-2.
I didn't get my laptop with a FTDI or other USB to serial port adapter to work. Maybe I needed to try further permutations, but the old computer worked, so I kept using it.
..
As for drives, I think my 5.25 drives seemed to work OK, but I only had 8" image files; I was worried (confidently worried) they would not work with the 5.25 drives as a system.
Someone GreaseWeazled my 5.25 discs and thought they seemed troubled, possibly many corrupted sectors.
I thought they seemed to read OK for the limited reads I tried. I've been hardwareless and skeptical since.
.
I had some code I wrote that I dumped into memory via teraterm and was able to format, read and write disks, but it was a pretty slow process and my code had some weakness.
I would share at the risk of sending you into the black hole of my few bytes.
.
I had 2 SA800 drives, but was having issues that I never got diagnosed.
.
I'll check back in a bit and see if Fritz wants my bits
Or if @Hugo can top the last tune (I'll start digging too).
 
I am still very occasionally playing with this system.
I've been distracted for some months; I have a situation difficult to discuss.
I really want this this thing to boot.
I'll try to update as soon as I can.
AJ gave me hand, maybe he cand send a PM if he can.
Thanks, Al (Troy)
Sorry - I forgot a song.... Give me a day or so,
 
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Troy bugged me along time ago to try the Greaseweazle; he actually bought me one and dropped it off, but the flux thing somewhat freaked me out when I only had a Shugart SA800-2 record of 77 tracks, of 26 sectors, of 128 bytes of an old FM image to deal with, 256256 bytes to be totally specific for an 8" disk.
How do I get this to become Flux .... ahhhhh
I just have to understand all the 1s and 0s before I try stuff; I love to jump off ledges into a pool of water, but I need to know the pool depth in this digital drop-off.
Once I looked close to the GW code it did alot to assist you and for core format of the disk *hopefully* will be covered for.
So the IMSAI has SA400 drives in it but I don't have SA400 images, but we also have a cabinet of 2x Shugart SA800-2 drives, and the IMSAI controller supports both.
The SA400 SD images are ~ 80KB per disk (128 byte sectors * 18 sectors per track/cylinder * 35 tracks/cylinders)
I have an old Shugart SA800-2 drive for this that Troy had in his stash.
For the image I have the SA800 drives want
FM mode
single side
360 RPM
250k bits/second
77 tracks
26 sectors per track
The Greaseweazle format dec.rx01 supported this
So the image I have is Cylinder 0 Sector 1, Cylinder 0 Sector 2 ... Cylinder 0 Sector 26, Cylinder 1 Sector 1 ... Cylinder 76 Sector 26 laid out, all 256256 bytes
I got a card off Eway TexElect to do the 34 pin to 50 pin adjustment from the Greaseweazle to my SA800-2.
I kept getting "Command Failed: GetFluxStatus: No Index"
I cleaned off my Index Detector on my SA800 and that went away
I then used command:
gw write --format=dec.rx01 imdos205r1-peters.dsk --drive=A
from a command prompt to successfully write the image to my 8" disk.
I need a trip to IMSAI land to try this out, but I always have a half full glass.
Let's hope we have a boot from this baby; I need a little upper.
Maybe Valerie is on my side:
 
Maybe in Heaven, or a bit below.
I visited my friends and IMSAI this weekend and had mixed results.
For this visit I started out setting both SA800-2 drives to DS1 (1-4)
with termination to all lines.
These have easy 0.100 shunts to use to select.
I wanted to test with one drive on the controller card at once,
and then switch to the other without changing jumpers.
I tried the first drive with my mdos205r1-peters.dsk disk in it seemed to behave somewhat
normally, read the first two 128 byte sectors and chew on it a bit.
Then start to read a bit more, I believe with some additional tracks read
(So easy with an exposed 8" drive ;-})
Nothing seemed to happen for a few tries.
Then gibberish on the teraterm port after a little while (maybe a few minutes)
(PS - MPU-B, 9600, 8-n-2, eight, no parity, and 2 stop bits is what I have been liking)
I switched serial port setting for multiple reboots trying to resolve the gibberish
and could not decide what was the output baud/settings could be.
I wanted to go home and get my scope.
Then I boot and serial works, kind of.
I wasn't sure, but not junk.
I typed in dir
and this thing printed the directory of the 8" disk I made from the GW.
Seems it may breathe!!!
I showed one friend, we smiled at brief success.
I couldn't repeat the dir, mostly no reaction from the disc after the first 2 sector read, and a subsequent read.
Tried the other SA800 we had and I had the servo kept crashing because of not detecting track 0
I decided to pull the somewhat good drive and take home to look at on the bench.
If it does not seem to be working we'll try Troy's that seems to work nice to create disks.
At this time you're all off the hook; I won't ask you to "call me" for help:
 
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I perhaps didn't say but that IMSAI box but with an MPU-A in it, VIO-C and a IKB-1 was my first computer. I was programming on it in a compiled Basic. Used WordStar for the editor. Mine I maxed out to 64k. It was reliable. The two 5-1/4" drives. Imdos -2.05. The two drives look to be upside down to my recollection but maybe I am not recalling correctly.
 
You do know the PDS requires a different capacitor on C2 depending on on the drive type you hook it up to. .0022 or ,01 uF depending on 5-1/4" or 8" drives. If you change it over you will definitely need to recalibrate the trim pots on the PDS according to the instructions.
 
Thanks Fritz for the echo in the IMSAI cavern I occupy; I appreciate the comments.
Nice hear from a legacy user of the PCS-80/35; Hope I can be one some day too ;)
I'd be quite thankful if you unexpectedly ran across a boot disk from your old accomplice.
.
It might bring you a nice dinner too.
I'd really like to understand file system organization; then maybe I could reverse engineer an image.
Any info on that would also be appreciated.
..
I took this unit apart a few times and probability would say that I have a 50/50 chance of having the drives in backwards.
I did a small search and found an image of the PCS-80/35 at the Computer History Museum.
Seems like I may have guessed right, or the doner of the unit was also left handed.
View attachment 1290624
.
I also looked into the capacitor. I found a note in the Imsai MDC-DIO User Manual on page 71 that said that the C2 cap change on the PDS board was necessary for the Persci
drives vs the other supported drives.
This had me a bit worried when you brought it up and I'll still have to confirm what I do have when I get back to the hardware.
No idea why the Persci needed this tweak to the design.
..
My present progress is I have one of the Shugart drives that seems to have read problems until warmed up.
The writes are even worse; even when the drive is warmed up I cannot successful full disk write a disk (again - this is on my bench with the Greaseweazle).
Sorry - no song tonight, but wanted to respond to MFF (My Friend Fritz)
 
You are correct about the drive orientation. I've got original Imdos on 5-1/4 SS disks and 8" floppies that presumably were used in Persci drives. Many require 56k of memory I believe. Some Imdos 1.3 and some 2.05.
 
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