Microprocessor controlled signal pattern detector

#The present invention relates to signal sensing for the purpose of detecting a special pattern of signals, and more particularly to utilization of a programmed processor for sensing and detecting a special pattern.

#In magnetic recording, and in particular magnetic recording on disc files, a double frequency recording technique is utilized. Double frequency recording involves the recording of magnetic flux transitions at a clock frequency, with binary data being represented by the presence or absence of a flux transition between clock flux transitions. This form of recording provides a means by which a variable frequency oscillator (VFO) can be made responsive to reproduced signals from the magnetic recording to synchronize and control the sampling of the recorded data.

#In magnetic disc recordings, each track is normally divided into a number of sectors, with each sector being comprised of various identifying and control characters for the purpose of data detection within the sector. One item of control information for the purpose of controlling further reproduction, is a field called an address mark. The fixed data content of an address mark field identifies the type of field which follows the address mark. The file control unit is caused to search for this particular data combination to control the use of the subsequent identified information. Since other portions of the recorded information may include normal data having the same data content as the address mark field being sought, a further form of signal detection has been incorporated into the detection of the particular data field. Address marks incorporate a special form of magnetic recording in which the binary data is interspersed with normal clock periods. However, instead of there being a magnetic flux transition for each clock period, certain flux transitions at clock times are eliminated from the recording. Therefore, a magnetic disc file control unit will recognize, with certainty, detection of the address mark, when the unique pattern of data is detected, along with the unique pattern of clocks and missing clocks within the eight-bit character being sensed.

#FIG. 1 is a representation of the format of magnetic recordings on a magnetic disc.

#FIG. 2 is a block diagram of the data flow of a programmed microprocessor utilized in the present invention.

#FIG. 3 shows the logic included in a disc file control unit utilized for purposes of address mark detection.

#In FIG. 1 there is shown a magnetically recorded disc 10 which is comprised of a plurality of recording tracks 11, each of which can be divided into a plurality of sectors 12. The format of each of the sectors 12 is as represented at 13.

#On each of the recording tracks 11, there will be an index mark 14 preceded by a gap 15 signifying the start of sector 1. The recorded portions labeled "GAP" are utilized for synchronization for following data. The first significant field of a sector is the sync field which is comprised of 6 bytes (8-binary bits) of recorded binary zeroes. The sync field is utilized for providing an initial indication that the next following field is probably going to be the address mark field 16 and synchronizes the detection circuitry. The addresss mark field 16 preceeds several bytes of encoded binary data called the ID field which is the identity of the sector to be compared with the identity of a sector being sought. The cyclic check field is an error detection code field for the ID field. The next following sync field preceeds another address mark field 17 which is coded with data identifying the next following field as a data field (FB) or a control field (F8). The next cyclic check field following the data field is another cyclic redundancy check field generated for the previous data field. Gap 3 signals the end of the first sector.

#To save time in searching for a particular sector, once the file control unit has received the identification of the sector required, an immediate search will begin for locating, and matching, the ID field. Since any of the information recorded on a particular track can take many forms, it is possible that a character detected in a data field or any other field, may in fact match the coded identification of the ID field of the sector being sought. Therefore, the file control unit must be informed of the exact location of the magnetic reproducing head to insure that the information being sensed is in fact the ID field of any sector. The technique for insuring that the ID field is being detected requires that it be preceded by the address mark field 16, which in turn is preceded by the sync field consisting of 6 bytes of zeros. Again, since many different forms of data can be recorded, it is conceivable that a data field might be comprised of 6 bytes of binary zeros followed by coded data which would be identical to the data in the address mark field 16, and also be followed by data that could conceivably match the coded data of the ID field.