Re: Write Signal on Disk II Question

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


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