Wtd: Northstar DD Disk Controller - MDS-AD3

[Moonferret]

Hi Folks!

Does anybody have a spare Northstar MDS-AD3 double density disk controller?
Also looking for some 16/32k S100 static RAM boards

Cheers,
Dave

 

[Dwight Elvey]

I'm curious, is this to be used in a NS system or other? The NS controller was a popular controller for many non-NS systems. The SOL commonly used the NS controller.
NS disk have been a problem for the GOTEK disk simulator systems. The NS controller is quite particular about sector timing. The timing for recovering data from USB drives is a little to slow to keep up with the timing required for the NS controller's sector timing circuit.
Dwight

 

[glitch]

NS disk have been a problem for the GOTEK disk simulator systems. The NS controller is quite particular about sector timing. The timing for recovering data from USB drives is a little to slow to keep up with the timing required for the NS controller's sector timing circuit.

Has anyone tried them with Mike Douglas's Virtual Sector Generator:

http://deramp.com/vsg.html

His VSG works very well with physical drives.

 

[Moonferret]

It's actually for a build I'm putting together in a TEI chassis. I already have an Altair 8800b and IMSAI running with this controller so I figured it would make sense to use the same. I've got a punch for converting soft sectored media so making a supply of disks isn't a problem

A friend of mine has successfully used one of Mike's VSG board with his N* Horizon although I think he had to swap the drives for direct drive units.

Cheers,
Dave

 

[glitch]

Can't go wrong with a TEI chassis! I hear they'll take an IMSAI front panel, even the little TEI boxes.

I've never tried the VSG with belt-driven drives since Mike recommended using direct-drive for stability, I'm not surprised that there's too much fluctuation with them.

 

[Moonferret]

Can't go wrong with a TEI chassis! I hear they'll take an IMSAI front panel, even the little TEI boxes.

The 22 slot chassis is almost identical to the IMSAI's and should be quite easy to fit an IMSAI front panel. I've had to fit switch mode power supplies in mine as the original power supply had been removed (Would have been 110V 60Hz and I'm in 230V 50Hz land)

Cheers,
Dave

 

[Dwight Elvey]

Has anyone tried them with Mike Douglas's Virtual Sector Generator:

http://deramp.com/vsg.html

His VSG works very well with physical drives.

I'm not sure that would help but it might. I think that is only part of the issue is that the GOTEK doesn't have enough space for the entire track of data. This means the GOTEK may not be able to deliver the desired data within the time frame expected by the controller. The fellow in France ( forget his name ) felt he could handle it the same way he deals with soft sectored and just hold off with that sectors data until is becomes available. This means he doesn't send continuous sector pulses. Using Mikes board may help because right now he does not create regular sector timing. He'd said it would require a rewrite of how the software works to include timer drive sector pulses. On soft sectored disk, most all systems only use the index pulse for formatting and "is the disk running". Otherwise the index to sector data relation is not important. If he is depending on this for the delays in fetching the USB data, it will not work, even with Mike's sector generator. I believe most GOTEK disk emulator software depends on this.
I've always wondered if SD serial is faster than the USB protocols? I understand SD better than USB and seems like it would be easier to modify a GOTEK to take a SD card to be the disk source. The uC can control the clock rate and as long as the allocation size on the SD was larger than a track, there should be no timing issue with transferring a track at a time, keeping up with both sector and index timing.
I have no problem ripping out the USB connector and putting in a micro SD connector. The STM32F105 may require some rewiring to get the SD interface to the leads used by the USB. It doesn't a have a complete cross bar and I don't think, even at 72MHz it can keep up with bitbanging the SD card while staying within timing of the disk data. It is best to have both running on DMA from timers.
Dwight

 

[Hugo Holden]

I use the MDS-AD3 controller in my SOL-20 and it works like a charm in conjunction with Mike's VSG that I built into a Takachi case with some Japanese made IBM drives:

http://www.vcfed.org/forum/showthread.php?66138-Floppy-Drive-for-SOL-20&highlight=Mike+douglas+VSG

The only quirk I found was not due to the N* card, or the VSG, it was the particular new old stock IBM drives I used, YD-580, are a beautifully made direct drive type (no belts and low jitter), but the chip set & wiring in them is designed to detect and reject (by not outputting sector pulses) if a hard sectored disk is inserted. I could probably disable that inhibition, but I have not needed to or tried yet as I'm happy with the soft sectored media.

 

[Dwight Elvey]

The Gotek doesn't keep the data aligned with the index pulse. That is why the VSG should not be able to work with the Gotek as a source. The VSG depends on the Index pulse being in the right place relative to the data. The current software on the Gotek depends on a variable delay between the Index and the actual data. This is fine for most all soft sectored controllers as they only look for address marks to define the beginning of sectors.
Mike's sector generator should have no issue with a true floppy. I was only talking about the Gotek that isn't a true floppy.
Dwight