Re: MFM drive gone nuts

From: Julian Perry <>
Date: Mon, 21 Jul 2014 01:10:51 +1000
Message-ID: <>
Hello Michał,

Monday, July 21, 2014, 12:05:52 AM, you wrote:

> Hello!

> Julian Perry wrote:

>> A quick googling found THIS URL :
>> It has the switch settings, including the various manufacturers
>> "Actuator Exerciser modes" for your drive.

> Thank you! This is exactly what I needed.



>> You are very unlikely to be able to read the format on a PC. Although
>> the raw encoding method may be similar, each controller manufacturer
>> (and even WITHIN the SAME controller manufacturer) used different sector
>> & header layouts. OMTI, Western Digital, NDC, DPT - they all had different,
>> mutually incompatible formats. The D9060/9090 used 256 byte Sectors,
>> so it's possible the C900 did too. The IBM PC XT/AT controllers used 512Bytes
>> per sector, so that's a likely showstopper right there.

> The C900 uses 512 byte sectors on the floppy, and the documentation says
> that it was done to match the hard disk. So I presume that the hard disk
> uses 512-byte sectors too.

> The controller itself is labeled WD1003-CMD. I wasn't able to find any
> information on the Internet on it, but a Google search shows that there
> were cards for PC labeled WD1003-xxx where xxx was some letter and
> number combination. So it looks probable that this controller uses the
> same format as these PC cards?

The 1003 was WD's first stab at the AT controller market (the 5170 had
its own IBM-branded monster - full length, OVER-full-height) - and had
a 5:1 interleave. I'd speculate the 1003-CMD is very similar to the
1003-WAH. The 1003 series was augmented by the compatible 1006V, which had a 1:1
interleave (240Kbytes/second). I seem to recall the 1006V could handle
1003-WAH format, but there was a quirk with the 1003 where the header
info duplicated the "head" info, so on drives with more than 4 heads
(0 thru 3) meant that the fifth head (4)had the same header info as the
first (0). I think this was due to the Reduced Write Current signal being
co-opted by the 1006 to address additional heads correctly: RWC was
usually handled by the drive, as soon as they became smart enough to
count where the head was.

Heavens, the technical ministrivia I seem to be able to dredge up from the
past - I'm getting old - the past looms ever closer, but the present
races away faster and faster....

<Speculation mode on:>  The 1003-CMD may be a Commodore-specific (?endian-reversed?)
version of the WAH. If so, it's likely MFM format compatible, but

> One other idea came to my mind: The controller has a 8749 CPU. It might
> be possible that this CPU died? Then obviously the controller would
> simply not respond to any commands from the computer in timely fashion,
> so the computer would think it's a timeout?

> Unfortunately my EPROM burner cannot read 8749 so I cannot check if the
> ROM contents are intact. I am looking for an adapter to do that.

If you can meter any activity on the DS or STEP lines of the
interface, that might indicate signs of life. The WAH controller has an
LED header - does the CMD have one, too?


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Received on 2014-07-20 16:00:03

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