dwight elvey dkelvey at
Sun Jun 1 12:06:41 CDT 2008

> From: lehmann at
> dwight elvey wrote:
>> Hi
>> My German isn't that good. If the step rate is the problem,
>> I did see a couple routines that were creating steps. One
>> was RAMP.
>> Setting the controllers step rate is always done on just one
>> port. I forget which. All you should really need to do is find
>> all the out's to that port and set the step to the auto rate.
>> For my code, it was only in two places.
>> Dwight
> Hm - I'm not sure what "auto stepping" means. Normally, the controller
> sends a "step" signal (after the direction is set) to the harddrive and
> the harddrive responds with a "seek complete" signal - and the controller
> sends so many step signals and waits for the seek complete signal (before
> the controller sends the next step signal) until the wanted track is
> reached. That is how it works, or? So what is "auto step" here?

 All MFM drive will take steps at some particular rate. The st251 had what is
called auto stepping as well. In this mode, one could send the steps at a 
very fast rate and the drive would save them into a counter. It would then
auto ramp the steps to a rate much faster than single steps could be done.
 I think it use the highest order head address but I don't recall exactly
how this was done. A quick search on the web should find it.
 Most of the newer MFM drives support autostepping and it is the perferred
stepping for these drives.
 You do not need to do single step seeks for the steps as you state, you
just set the destination cylinder, direction and send steps at the rate specified
by the drive. You don't look for "seek complete" between steps, you just
send steps at the rate specified. When you believe you reached the desired
cylinder by the number of steps, you look for "seek complete" and not
 The ST251 can except controller rate stepping or auto stepping.

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