TashTwenty: Single-Chip DCD (Hard Disk 20) Interface

[tashtari]

Where did you buy the 7pin SD card reader?

Oh, sorry, thought I had posted this already... it's from SparkFun: https://www.sparkfun.com/products/13743

 

[olePigeon]

Update: It is possible to eject a DCD that has the ejectable flag set, but it comes right back immediately, and there doesn't appear to be a command being sent that could mean "eject media" or anything similar. The only thing I wonder about as I look at the trace is that sometimes the byte after the command byte in the Controller Status command is 0x00 and sometimes it's 0x01. I don't know what the significance of this is. It'd be a weird way to ask the drive to eject, but that doesn't rule it out. If there's an answer to this question, it probably lies in the depths of the driver code. BMOW posted a decompiler listing with some comments, though damned if I can make much sense of it. Anyone care to dig in?

The HD20 doesn't have media, per se, to eject. I really hope someone on here wouldn't mind taking a stab at it. I would LOVE to have a Floppy adapter that enables daisy chaining by converting a FDHD into a block device. This would be a dream come true.

 

[tashtari]

The HD20 doesn't have media, per se, to eject.

This is true, but the DCD specification was meant to accommodate storage devices of all types, and there's an "ejectable" bit and a "disk in place" bit in the Controller Status response, which suggest that removable media was considered too. In that case, though, I'd expect that there would be a command sent to a DCD that was listed as "ejectable" to eject its media (after which "disk in place" would read 0) but I set a TashTwenty up with these bits set and watched the bus traffic and didn't see one. It could be that it was just never implemented in the ROM, but I can't say for sure because reading the ROM code is an exercise in self-induced headache...

 

[olePigeon]

I wish I was smart and could help somehow. Maybe @bigmessowires could comment. Dunno if he still visits the forums.

 

[dochilli]

What are the values of the resistor (10 kOhm?) and the capacitor?

 

[tashtari]

What are the values of the resistor (10 kOhm?)

10 kohm is what I used, it's a pullup resistor for the MISO line from the card.

and the capacitor?

10 uF is what I used, it's a decoupling cap across supply and ground. Make sure you get a low-profile one so there's room for the SparkFun board to fit over it.

Assuming you're building one for yourself, I look forward to hearing how it works for you. =D

Another thought: Have the PCB fabbed at 1.2 mm or less, that way it'll fit in between the pins of the "DB"-19 connector.

 

[micheledipaola]

Will assembled boards be available in some (near?) future?
that would be amazing...

 

[tashtari]

Will assembled boards be available in some (near?) future?

If there's enough interest, I could see getting a few of my design made for sale, but @demik was working on one as well and may be in a better position for it than I am.

Is anyone else interested in buying? If so, please let the thread know. =)

 

[micheledipaola]

If there's enough interest, I could see getting a few of my design made for sale, but @demik was working on one as well and may be in a better position for it than I am.

Is anyone else interested in buying? If so, please let the thread know. =)

I would. If price is reasonable, I would consider a couple units.

 

[olePigeon]

@tashtari This might be outside your knowledge, but, could this be adapted to support the Apple PC floppy drive? Sure would be interesting to have an adapter that would let you connect the Apple PC 5.25" drive to the Mac's floppy port. However, Apple used an entire NuBus or SE PDS card to accomplish it, so I don't know if it'd even be remotely possible.

 

[NJRoadfan]

The PC 5.25" was basically a standard shugart interface drive in a custom Apple case. The interface card had a NEC PC compatible MFM controller on it.

 

[mactjaap]

If there's enough interest, I could see getting a few of my design made for sale, but @demik was working on one as well and may be in a better position for it than I am.

Is anyone else interested in buying? If so, please let the thread know. =)

Sure! I like to test.

 

[olePigeon]

The PC 5.25" was basically a standard shugart interface drive in a custom Apple case. The interface card had a NEC PC compatible MFM controller on it.

Wasn't the HD20 an MFM drive?

 

[Tugboat]

Wasn't the HD20 an MFM drive?

I would. If price is reasonable, I would consider a couple units.

Me too.

 

[dochilli]

I ordered 5 PCBs from China (15 Euros). I will write about building the TashTwenty. One problem may be getting the 19pin DB, but for my first attempt I can use a 25pin DB and cut some pins out.

 

[cheesestraws]

Wasn't the HD20 an MFM drive?

All MFM really means in this context is the way that the data is encoded as magnetic transitions on the disc surface. It doesn't mean that anything else is common about the mechanism of the drive or the way it communicates...

 

[tashtari]

One problem may be getting the 19pin DB

There are some sellers on ebay, or you can order them from IEC, which has the world's worst online store (I just ended up calling them).

 

[olePigeon]

All MFM really means in this context is the way that the data is encoded as magnetic transitions on the disc surface. It doesn't mean that anything else is common about the mechanism of the drive or the way it communicates...

Oh ok. A bit confusing. I assumed it was only a method by which to connect a device like SCSI or IDE.

 

[cheesestraws]

Oh ok. A bit confusing. I assumed it was only a method by which to connect a device like SCSI or IDE.

It is confusing . Made more so by that for hard discs there is I think a kind of semi-standard for what that inferface looks like in a kind of handwavy way (this is out of my competence really, so I don't want to say too much about it an expose myself as a fool!). But the fact that a floppy drive and a hard drive both use MFM doesn't mean that they're necessarily much alike in terms of interface, just in terms of data encoding.

It is, as usual, a terminological mess.

 

[olePigeon]

Yeah. On the HDDs they have that weird two-ribbon cable deal going on. I always forget which one is which, but you can daisy chain an additional HDD off one of the cables.