ImageDisk / PC FDCs & single-density

Dave Dunfield dave06a at
Wed Mar 22 06:12:00 CST 2006

>  > It uses a DP8473AV as the floppy drive controller IC.

[Al Kossow]
> has the data sheet and a app note for the data
> separator, which is more sophisticated than the
> one normally found in a 765.
> I assume there's a way to deterimine if you have
> a 8473 in software.

Thanks Al - I will check it out and see if I can determine
any possible explainations...

[Chuck Guzis]
> Maybe so, but I can tell you with 100% certainty that neither TeleDisk nor
> TESTSD performs any sort of test for one.  The command "MFM" bit is the
> only consideration (other than the data clock) that's made for FM vs. MFM
> recording. 

Thats what I had assumed (thanks for confirming). I do exactly the same. I
set the appropriate data rate in the register at 3F7/377, and select FM/MFM
by the absense or presense of the MF bit (6 - 0x40) in all related commands.

During analysis, IMD cycles through the six possible combinations (250, 300
and 500 kbps at both FM and MFM) as it tries to identify the disk. I've not
seen another case yet where a disk was readable on the PC and IMD could
not detect it correctly, no matter what drive type and data rate.

Even if the analysis was failing, IMD configures the controller directly to the
desired mode and data rate when writing, and the user reports that he cannot
write my images either. If anyone has any idea as to what I might have missed
or misinterpreted in the specs that could cause this, please let me know.

Does anyone else have an Adaptec 1522A controller that you can try with my
latest version of ImageDisk to see if you can read/write single-density disks?
I don't have this controller to test with, and I would like to confirm that the
problem is generic and not related to the one particular unit in question.


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools:
com             Collector of vintage computing equipment:

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