Browse Prior Art Database

Transition Detector for Dasd Write Operation

IP.com Disclosure Number: IPCOM000100595D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 91K

Publishing Venue

IBM

Related People

Turner, DP: AUTHOR

Abstract

The invention disclosed is a technique for detecting the presence of write transitions at the write head of a direct access storage device (DASD) and verifying that the detected transitions represent the data to be recorded.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Transition Detector for Dasd Write Operation

       The invention disclosed is a technique for detecting the
presence of write transitions at the write head of a direct access
storage device (DASD) and verifying that the detected transitions
represent the data to be recorded.

      In current DASD products, one of the write safety circuits,
used to insure the integrity of the write operation, is the
transition detector.  The transition detector monitors the waveform
across the write head to ensure that the current in the head is
reversing polarity. In current DASD products, the transition detector
is a re-triggerable single-shot which is triggered by a transition of
one polarity.  The single-shot time out is long enough that in normal
operation the recurring transitions keep the single-shot from timing
out.  When transitions are missing, the single-shot times out,
indicating missing transitions.

      The disadvantage of the conventional transition detector is
that it does not detect isolate missing transitions.  Thus, some
faults in the write data path are not detected.  If the write signal
across the head is compared with the transmitted write data in a wrap
back check, an improved transition check is made.  The invention
disclosed here is such an improved transition check.

      Fig. 1 is a block diagram of the invention.  The blocks in the
top half of the diagram (write trigger, write driver, write head and
select amplifier) are all components found in any write channel.  The
added components of the invention are shown in the bottom of the
block diagram (comparator with hysteresis, two "D" flip-flops and an
exclusive OR (XOR)).  The return-to-zero w...