Re: Write Signal on Disk II Question

[Mike Willegal <mike@willegal.net>]

Bryan,

The field being generated is never absent when writing, it is changed in 
polarity for each one bit.  This is not a digital (on or off) signal.

Regards,
Mike Willegal

Bryan Parkoff wrote:
> Mike,
>
>
> > I'm not sure if I entirely understand your question, but I'll give it a 
> > try.  When reading the disk, the controller derives it's timing from the 
> > changing state of the fields.  If you wrote eight ones and simply left the 
> > field in a constant state,  the controller would have a hard time 
> > determining where one bit ended and another one started and the timing 
> > would most likely be hopelessly out of whack after a just a few bits. This 
> > is why there are requirements in each code word for limiting adjacent 
> > zeros (which do not change the field) and manditory ones (which do change 
> > the field).
>
>
>     Okay...I am talking about Write Sequence, but not Read Sequence.  You 
> can write more than 3 ZERO bits to the disk without any problem.  The Read 
> Sequence is not able to read more than 3 zero bits reliably.  I am trying to 
> ask for the answers to my questions. My question -- Eight ONE bits is stored 
> in the data register and one bit is shifted out 8 times.  The Write Signal 
> toggles from low to high or high to low each bit.  It looks like four 
> present field reversals and four absence field reversals.  Please explain 
> more in details how 8 ONE bits are stored between field reversals.  Please 
> note that I talk about field reversals and Write Signal in Write Sequence.
>
> Bryan Parkoff