How to access "real" floppy disk over FDC

[Dieter Schneider]

Hi Guys,

I already integrated successfully my FDC and was able to connect 2 drive to it.

Drive 1  is a 5.25" TEAC FD-55GFR

Dive  0 is a 3,5" Teac FD-235HG

Both drives I can access via the serial terminal from the FDC and read out e.g. drive information via I 1

This would print for my 5.25 drive:

On the DIP Switch all single switches are in OFF posistion - hopyfully thats correct.

So but how do I access those drives from CPM or Basic?

I tried these steps accoding to the instructions from :https://retrocmp.de/hardware/altair-8800/altair-duino_guides.htm#88hdsk

SW15 to SW0: 0 000 000 000 000 001
Hold deposit + Turn ON

SW15 to SW0: 0 011 000 000 000 000
AUX2 down

SW15 to SW0: 0 011 000 000 000 011
AUX2 down

[mounted hard disk image 'HDSK03.DSK:
Mike Douglas' 88-HDSK CP/M' in platter 0 of unit 1]

SW15 to SW0: 0 000 000 000 001 110
AUX1 down

[Running Hard disk boot ROM]

After booting into CP/M I tried to enter
A>B or A>B:

By entering A>B I am getting
B?

By entering A>B: I am getting
Bdos Err on B: Bad Sector



On both drives I dont see any activity on the LEDs :-(

BR 
Dieter

[fridtjof.ma...@gmail.com]

That HD BIOS has : A: hard disk platter B: hard diskplatter, C: floppy D: floppy

[Chris Davis]

Here's the easy way:

1. Copy a DSK file to a floppy using David's serial interface on the drive controller.  I'd suggest copying DISK01.DSK (CP\M).  

2. Boot the Altair-Duino in default mode (no ROMs or floppy/hard disk images loaded).

3. Insert the real physical floppy you created in step 1 and close the drive door.

4. Turn on SW3 and lower AUX1.

5. System should boot from floppy to CP\M.

In your example, I don't know what "A>B" is supposed to do, but in that configuration I think entering "C:" would change the current drive to whatever you have inserted in your floppy drive.

[Dieter Schneider]

Hi All, 

two things:

1)

I was able to upload via Serial Connection on FDC an image for DISK001.DSK on my drive 0 which is the 3.5" Floppy drive.

When booting CPM from this disk it seems to work but I get couple of error like "Bdos Err on A: Bad Sector" - hitting Enter a couple of times until error message is gone - then I can load also programs.

How to get rid of that error?

2) I swapped on the DIP (second DIP Switch) on FDC drive A and B so that drive 0 will become my 5.25 drive and drive 1 will be the 3.5"

But when I try to load the same image onto the 5.25 drive, I am getting this error:

How can I solve this?

Thx 

Cheers Dieter

[da...@hansels.net]

The "bad sector" error is hard to diagnose. It is POSSIBLE that your 3.5" drive is not spinning very consistently. That is not a problem with the soft-sectored formats that these drives were usually used with but for the hard-sectored Altair format a consistent rotation speed is essential. You can try issuing the command "F 0,3" in the serial monitor. That will set some (experimental) flags that may help compensate for the rotation. Note that this assumes the drive with the problem is drive 0, use "F 1,3" for drive 1. Not sure if that will work. I think Tom Lake had similar problems and ended up getting a new(er) 3.5" drive which solved the issue.

The "No track 0 signal detected" error means that the controller has issued more than 80 step commands to step towards track 0 but the drive's "track 0" sensor has not engaged. That means that either the stepping is not working or the track 0 sensor is not working. In the serial monitor, issue the command "i 5", which should step the drive 5 steps in (away from track 0). Do you hear the head stepping sound? Try "o 5" which will attempt to step in the other direction. If you can't hear stepping noises then the problem is likely with the stepper motor. Check if the drive gets both the 5V and 12V power. If the stepping works then take a closer look at the track 0 sensor. I think there are some maintenance manuals for the FD-55GFR online where you can find some more details about where the sensor would be.

[Dieter Schneider]

Hi David,

I set the FLAG "F 0,3" in the serial monitor and since then, everything is working great.

Is that flag persistance on the FDC? Because I turned off voltage on AD (and FDC) and also on my diskdrive and aftering powering up everything is fine.

Can work great unter CPM with the 3.5" drive.

The other drive (5.25) I am going to analyze the next upcomming days. 

Will keep you und track how the progress is :)

THX

Dieter

[da...@hansels.net]

Yes, the flags are persistent. If you want to turn them off and go back to the original behavior use "F 0,0".
Note that you are setting the flags for drive 0 so if you move the 3.5" drive to the other spot on the cable
then you need to set flags "F 1,3".

[Dieter Schneider]

Hi David,

today I analyzed the "No track 0 signal detected"

First of all the the stepper motor is moving according to the command i 5 and o 5 or with other values like i 10 / o 10

So this seems to be OK.

I uploaded here a video to see: 

https://youtu.be/rV4fBZoHjZk

What worries me a bit, if I turn on the power supply for the drives, the 5.25" makes a real loud terrible noise for 1 second - is that normal - as louad as a door bell ;-) 

The same loud noise appears also when I enter the W 0 command to upload an disk image.

next video for listing the noise is here:

https://youtu.be/BY_SQprV4vk

BR
Dieter

[da...@hansels.net]

The noise for the "W" command is the result of the controller trying to step to track 0,

not seeing the "track 0" signal and continuing to step even though the head is already
at the end and going against the end-stop. Obviously not normal.

You need to figure out why the "track 0" signal (pin 26 of the floppy disk cable) does not
go LOW when the head is all the way out. You can test this even without the controller.

Connect pin 26 of the cable via a 1k resistor to 5V (as a pull-up) and then measure

voltage on that pin. It should go LOW if the head is on the outside track and back high
otherwise. Or keep the controller connected (already has the pull-up built in) and measure
on the PCB where the cable connects.

[Dieter Schneider]

I found the issue.

The mechanical part for the photo sensor was broken. I fixed it and now I get low signal on track 0 - also no strange noise any more on startup.

After fixing this stupid issue I am able to upload disk images on my vintage 5.25 drive and be able to boot that image as well :)

Thx you David :)

I am very happy now