Patent Abstract:
An apparatus and associated method are described for use in a disk drive including a disk that that is supported for controlled rotation and for cooperating with a transducer arrangement for accessing the disk in performing a data operation. The disk includes an arrangement of servo track wedge segments for storing servo data such that a set of servo data is periodically available as the disk is rotated in relation to the transducer arrangement and the servo track wedges are separated by an arrangement of user data wedge segments for use in storing user data. Generally, a controller IC and a channel IC are provided. The servo data is transferred from the channel IC to the controller IC using one data protocol and user data is bidirectionally transferred between the channel IC and the controller IC using a different data protocol.

Full Description:
BACKGROUND 
   The present invention is generally related to disk drives and, more particularly, to a transformable data interface that is used in a disk drive. 
   Modern disk drives, particularly, hard disk drives typically utilize what is referred to as an “embedded servo” format. A disk, in accordance with this system, includes wedge-shaped regions of servo data which separate regions in which user data can be stored during write operations and retrieved during read operations. These read and write operations are coordinated and controlled, based on the servo data, in a well-known, although complex manner. One approach in attempting to improve the handling of servo data versus user data is seen in U.S. Pat. No. 6,278,568 issued to Cloke et al. (hereinafter the &#39;568 patent), as will be discussed immediately hereinafter. 
   A typical hard disk drive includes a channel IC that is configured for processing information as it is received from one or more disks within the drive, as read by a transducer arrangement, and for preparing information to be stored by the drive, using the transducer arrangement. It should be appreciated that the information retrieved by the transducer arrangement is essentially analog in form. The channel IC serves to convert both analog servo information, as well as user data that is read from the disk to digital form. In this regard the &#39;568 patent illustrates such a channel IC in FIG. 1D, indicated by the reference number 26. Such a channel IC is often interchangeably referred to in the art as a read/write channel, read/write IC or, more simply as a channel. With regard to the type of processing that is performed by the channel IC, servo data is transferred unidirectionally from the disk to the channel IC and beyond, whereas user data is bidirectional. That is, read user data travels in the same direction as servo data from the transducer arrangement to the channel. Thus, processing of the read user data and the servo data can be shared by some components in the channel. Write user data, on the other hand, passes oppositely from the channel to the transducer arrangement. User data is generally handled in the form of NRZ data in a parallel format. In the example of the &#39;568 patent, FIG. 1D, a channel bus 38 transfers this NRZ user data, i.e., both read user data and write user data, to and from a host interface and disk controller (HIDC) 32. It is noted that this arrangement is typical of the prior art for purposes of transferring user data between a channel IC and a controller IC. It is important to understand, however, that there is other information that is needed by the controller. In particular, the controller needs the servo information. This is complicated by the fact that the servo information is not in the NRZ parallel format that is required by channel bus 38. The typical approach of the prior art, with respect to transferring servo data, is to provide dedicated physical lines between the channel and controller in order to support transfer of the servo data. The &#39;568 patent, in contrast, takes a different approach, as will be described immediately hereinafter. 
   With respect to transferring servo data from channel 26 to controller 32, the &#39;568 patent describes its approach, for example, at col. 15, lns. 17-20. The patent converts the servo data to the format of the NRZ user data and then transfers the servo data on channel bus 38 to controller 32. While this approach does limit the number of physical connections between the channel and controller, it is submitted that the conversion process and subsequent data recovery is difficult at best. For example, the channel bus operates according to its own clocking signal and protocol whereas the servo data is essentially in the form of serial data that is provided in timed relation to its own serial clock and according to a serial data protocol. Further, the &#39;568 patent describes the transfer of servo burst data at col. 10, lns. 2-8, via a microprocessor 120 on a microprocessor bus 36 that is separate from channel data bus 38. Thus, it appears that only part of the servo data is being transferred on channel bus 38, resulting in a complex process, at best. An approach that does not require such a difficult conversion process or complexity would be desirable. 
   The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
   SUMMARY 
   The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
   An apparatus and associated method are described for use in a disk drive including a disk that that is supported for controlled rotation thereof and for cooperating with a transducer arrangement for accessing the disk in performing a data operation. The disk includes an arrangement of servo track wedge segments for storing servo data such that a set of servo data is periodically available as the disk is rotated in relation to the transducer arrangement and the servo track wedges are separated by an arrangement of user data wedge segments for use in storing user data. 
   Generally, a controller IC and a channel IC are provided. The servo data is transferred from the channel IC to the controller IC using one data protocol and user data is bidirectionally transferred between the channel IC and the controller IC using a different data protocol. 
   One embodiment involves, by way of example, a controller IC is provided including a controller port and a channel IC includes a channel port that is configured for communication with the controller port, at least for periodically recovering the set of servo data for use in coordinating the data operation based, at least in part, on the servo data to handle the user data in a predetermined way. An interface includes a first portion that forms part of the channel IC, a second portion that forms part of the controller IC, and an arrangement of electrical conductors that connects the controller port of the controller IC with the channel port of the channel IC. The servo data is transferred from the channel port to the controller port and the user data is transferred between the channel port and the controller port. The first portion and the second portion are configured to cooperate for transferring the servo data across the arrangement of electrical conductors according to a first data protocol and for transferring the user data across the arrangement of electrical conductors according to a second data protocol, which is different from the first data protocol. 
   In another exemplary embodiment, a channel IC includes a first section that is configured for processing the set of servo data as read from the disk for a control use. A second section is configured to cooperate with the first section for processing the user data, which can pass bidirectionally therethrough as user read data when being transferred from the disk and as user write data when being transferred to the disk. A channel port forms part of the channel IC and is configured for externally transferring the set of servo data according to a first data protocol during a first data interval using a set of electrical conductors that are externally interfaced and for bidirectionally externally interfacing said user data according to a second data protocol, that is different from said first data protocol, during a second data interval, in timed relation to said first interval, using said set of electrical conductors. 
   In still another exemplary embodiment, a controller IC is configured for cooperatively interacting with a channel IC. The controller IC includes a controller port that is configured for receiving the set of servo data from the channel IC according to a first data protocol and during a first time interval and for bidirectionally communicating the user data through the controller port according to a second data protocol that is different from the first data protocol and during a second time interval in timed isolation from the first interval. A servo section is configured for using the set of servo data received from the controller port to control the transducer arrangement in accessing the disk. A user data section is configured to cooperate with the servo section for processing the user data, which can pass bidirectionally therethrough as user read data from the controller port and as user write data to the controller port. 
   In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 

   
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be illustrative rather than limiting. 
       FIG. 1  is a block diagram illustrating one embodiment of a hard disk drive. 
       FIG. 2  is another block diagram illustrating further details with respect a portion of the hard disk drive of  FIG. 1 . 
       FIG. 3  is a flow diagram illustrating the initiation and transfer of servo data, using the hard disk drive of  FIGS. 1 and 2 . 
       FIG. 4  is a flow diagram illustrating the initiation and transfer of read or write user data, using the hard disk drive of  FIGS. 1 and 2 . 
       FIG. 5  is a timing diagram which illustrates the relationship between transfers of servo data, user read data and user write data. 
   

   DETAILED DESCRIPTION 
   Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles taught herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein including modifications and equivalents, as defined within the scope of the appended claims. It is noted that the drawings are not to scale and are diagrammatic in nature in a way that is thought to best illustrate features of interest. Descriptive terminology has been adopted for purposes of enhancing the reader&#39;s understanding, with respect to the various views provided in the figures, and is in no way intended as being limiting. 
   Turning now to the figures wherein like reference numbers are used to refer to like components whenever possible throughout the various figures, attention is immediately directed to  FIG. 1  which illustrates a hard disk drive (HDD) that is generally indicated by the reference numeral  10 . Disk drive  10  includes a head disk assembly  12  having a disk arrangement  14  that includes at least one disk that is supported for controlled rotation using a spin section  16 . A VCM section  18  controls HGA  12  that is supported for pivotally moving a transducer arrangement  24  in controlled relation to any suitable number of disk surfaces in disk arrangement  14 . A preamp section  30  is in bidirectional electrical communication with transducer arrangement  24 . A servo/spin IC  40  provides control signals to spin section  16  and to VCM section  18  in a well-known manner using a spin driver section  42  and a VCM driver section  44 , respectively. The servo/spin IC further includes an interface and control section  46  that provides external interfacing in a well-known way, receiving a clock signal from a system clock generator, or other suitable source, and a serial I/O communication interface, both of which are yet to be described. 
   Still referring to  FIG. 1 , drive  10  includes a channel IC  70  that handles data to and from transducer arrangement  14 , via preamp  30 . This data includes servo data, for use in positional control, and user data which may be involved in a write operation or a read operation. Servo data and user read data travel from preamp  30  on an analog data path which, in the present example, includes a variable gain amplifier (VGA) section  72 , a continuous time filter (CTF) section  74 , a finite impulse response equalizer (FIR) section  76  and is terminated by an analog to digital converter (A/D) section  78  which generates a digital signal based on either read data or servo data. Each of these sections is well-known in the art and, as such, will be briefly described. Further, any suitable componentry may be utilized in the analog path and the present application is not intended to be limited to the exemplary components shown here. As one example, a digital FIR section can be used, which would be on the output side of A/D converter  78  in  FIG. 1 . 
   During a read or servo data handling operation, preamp  30  receives information, in analog form, from transducer arrangement  24  and amplifies the information for receipt by VGA section  72 . In this way, the latter can provide a signal to CTF  74  that is reasonably constant. CTF  74  generally serves to filter out noise in the manner of a low pass filter with programmable bandwidth and boost. The CTF presents a relatively sharp cut off frequency. FIR section  76  essentially appears as a form of a tapped delay line having a set of tap weights that are programmed by a servo and synthesizer section  80 . It is noted that this latter section also controls analog to digital converter section  78  since both FIR section  76  and analog to digital converter section  78  are set to function differently for servo data than for read or user data. For example, the tap weights are changed in the FIR section while the analog to digital converter uses different sample rates. It is noted that the &#39;568 patent, described above, provides details with respect to a digital FIR section with reference to FIG. 10 of the patent. Servo and synthesizer section  80 , in its synthesizer function, includes a servo clock synthesizer portion and a data clock synthesizer section. The former produces a generally constant servo clock signal, while the later produces a data clock reference signal that changes at least on the basis of the relative radial position on the disk, as is known in the art. It should, therefore, be appreciated that the servo clock signal and the data clock reference signal can necessarily be of different frequencies. This requirement may change in future servo systems since a “zoned” servo arrangement may be used where the frequency of the servo signal changes based on radial position on the disk. Analog to digital converter  78  also provides its output to a digital phase locked loop (PLL)  82 . The latter is used in a well known manner as part of a feedback control system for purposes of controlling the servo clock signal and the data clock reference signal. That is, the data clock reference signal is synchronized to the NRZ data that is coming in, for example, in a user read operation. It is noted that the data clock signal changes in frequency on the basis of radial position on the disk. The speed of the user data can change for other reasons such as, for example, if the disk speed changes slightly. Irrespective of the cause of the irregularity in frequency, this closed loop feedback system causes the data clock reference signal to remain locked to the incoming data. In effect, A/D converter  78  is caused to sample the incoming signal at the proper points on its waveform. This system responds similarly with respect to servo data with the exception that the closed loop control is directed to the servo clock signal. It is noted that there are methods in the prior art where the data is not locked to a PLL but is sampled and, thereafter, interpolation between these samples is performed, for purposes of recognizing equivalent data information. 
   Still referring to  FIG. 1 , once analog to digital converter  78  has provided digital data, the latter flows differently on the basis of whether it is servo data or user data that was derived in a read operation (i.e., user read data). In the present example, recovered user read data is processed by a Viterbi section  100 , which carries the name of its inventor, is well known in the art and may be referred to interchangeably as a maximum likelihood detector. The latter functions by sampling the voltage on the waveform at its input and compares these samples with a set of rules. When the data does not conform to the rule set, the maximum likelihood detector corrects the data. It should be appreciated that there may be errors in the data for a number of reasons which include, but are not limited to noise and disk imperfections. 
   The recovered user read data output of maximum likelihood detector  100  is provided to an encoder/decoder (ENDEC) section  102 . For purposes of processing user read data, the ENDEC is in its decoder mode. The incoming data is decoded to produce NRZ data which is provided to a data interface  104  and handled as will be further described below. It is noted that at least portions of the servo data may pass through maximum likelihood detector  100 . For example, the grey code can pass through detector  100 . This information then rejoins the remainder of the servo data for subsequent handling therewith. 
   Servo data, on the other hand, is provided from analog to digital converter  78  to a servo processing section  110  and is controlled by servo and synthesizer section  80  in a well known manner to generate a servo clock signal and servo data which are then available to a servo data control section  114 . Thus, both user read data and servo data paths have reached data interface  104  and servo data control section  114 , respectively, at which point this data must then be transferred to a controller IC  200 , as will be further described below. User write data, on the other hand, is received from controller IC  200  by data interface  104  in NRZ format, or other suitable format, and is then transferred to ENDEC  102  with the latter being configured in its encoder mode. From data interface  104 , the NRZ user write data is handled in a well known manner in the channel IC by being encoded by ENDEC  102  and then provided to preamp  30 . The preamp then transfers the encoded information to transducer arrangement  24  for recording on disk arrangement  14 . 
   Attention is now directed to further details with respect to  FIG. 1 . In particular, controller IC  200  includes a disk processor  400  that controls the described data flow operations using a number of connections that have not been illustrated for purposes of clarity, for example, by reading buffers and registers and acting on the basis of data stored therein. Processor  400  also generates servo gate (SG), read gate (RG) and write gate (WG) signals that are used for controlling the drive in a manner that will be familiar to one having ordinary skill in the art and as will be further described at one or more appropriate points below. These signals are provided to a mode control section  404  in channel IC  70  which will be described in further detail at one or more appropriate points below. Like servo data control section  104  in the channel IC, a serial servo data in (SSD IN) section  410  is connected to a subset of an overall arrangement of NRZ lines that connect channel IC  70  to controller IC  200 . The full set of these NRZ lines, which may be referred to as an NRZ bus, is connected between data interface  104  in channel IC  70  and a disk ports section  412  in controller IC  400 . Servo serial data in section  410  and disk ports section  412  serve as repositories for servo and user data, respectively, which can be acted on in any number of ways once received therein, for example, by disk processor  400  or for purposes of performing error correction. It should be appreciated that the servo data path is one-way from channel IC  70  to controller  200  and section  410  is therefore labeled as “SSD IN,” whereas the user/NRZ data path between data interface  104  and disk ports section  412  is a two-way or bidirectional data path. Thus, user data passes through this latter path for both read operations and write operations, although in opposite directions. 
   A clock generator  430 , which may be a crystal controlled oscillator in controller IC  200 , provides a clock signal for use therein as well as for use by channel IC  70  via a reference clock buffer  432  and by servo/spin IC  40  via interface and control section  46 . Disk processor  400  uses interface and control section  46  to coordinate the operation of spin driver section  42  and VCM driver section  44  via a first serial I/O section  440 , forming part of the controller IC and a second serial I/O section  442 , forming part of the channel IC, and all of which are connected by a serial I/O bus  444 . It should be appreciated that this form of control arrangement is well known in the art, as related to the use of a channel IC, controller IC and spin/servo IC and can readily be adapted to modified forms of IC topologies and configurations. 
   Referring to  FIG. 2  in conjunction with  FIG. 1 , a more detailed illustration is provided with respect to portions of system  10  that relate to the transfer of servo data from channel  70  to controller  200  and the transfer of user data between channel  70  and controller  200 . In particular, clocking and control logic is illustrated which includes a data clock control section  500  and a controller side (CS) clock logic section  502 . Mode control section  404  receives read gate, write gate and servo gate to provide control signals based on these inputs which distinguish operation for purposes of retrieving and processing servo information from processing user data, that can be in the form of user read data or user write data. Accordingly, serial data control section  114  receives a servo mode signal  504  from mode control section  404  which indicates to the serial data control section that servo data is present and should be processed. Mode control section  404  also provides a data mode signal  506  to data clock control section  500  which indicates that NRZ/user data is to be processed. Such mode control signals generally serve to place these sections into an appropriate mode, based on the servo gate, SG, signal. That is, in the presence of SG, the serial data control section processes servo data in a servo data mode, while deassertion of SG causes the system to process user data in a user data processing mode. Read data can be processed during SG, due to read latency, as will be further discussed below. The type of user data that is to be processed is determined based on the Read Gate, RG, and Write Gate, WG, signals. It should be appreciated that most disk drives use these signals in a well known way that is consistent with there use herein. Further, these control signals or derivatives thereof are readily available in controller  200  since they are produced by disk processor  400 , as described above with respect to  FIG. 1 . 
   Continuing to refer to  FIGS. 1 and 2 , data clock control section  500  receives a data reference clock from a data clock synthesizer  510  that forms part of servo and synthesizer section  80  of  FIG. 1 . This clock signal is phase locked to the user data using PLL  82  of  FIG. 1 . Thus, section  500  can provide NRZ based clocking signals, as needed. In particular, clock signals are provided to a serial to parallel shift register  520  on a line  522 , to an input/output latch  524  on a line  526  and to CS Clock Logic section  502  on a line  527 . It is noted that serial to parallel shift register  520  and input/output latch  524  form parts of data interface section  104  of  FIG. 1 , illustrated in  FIG. 2  using a dashed rectangle. Serial to parallel shift register  520  receives information from a read path processing block  528 . In the present example, read path processing block  528  includes Viterbi  100  and ENDEC  102  (see  FIG. 1 ) which receive digital data from A/D converter  78  as the terminus of the analog path from preamp  30 . On the other hand, serial to parallel shift register  520  can send user write information to a write path processing block  530  which is then passed to the analog path leading to preamp  30  and includes ENDEC  102  (see  FIG. 1 ). Serial/Parallel shift register  520  includes a parallel interface  532 , for example, eight bits wide, or some other chosen width, that connects to Input/Output latch  524  and which is enabled by data clock control section  500  via a line  533 . The latter further includes a buffer section  534 , that is tri-statable, connected to an eight bit NRZ bus  540 , with individual conductors of the bus indicated as B 0 -B 7  as these lines operationally pertain to their NRZ bus functionality between the channel and controller, such that the buffer section may terminate the NRZ lines with a high impedance or be placed into an enabled or active mode for reading from the NRZ lines or for driving data onto the NRZ lines. In this way, buffer section  534  is essentially disconnected from the NRZ lines in the tri-state mode such that these lines can be used for other purposes, yet to be described. When it is desired to use the NRZ lines for communication with controller  200 , buffer  534  is placed into an active or enabled mode using a line  536  that is connected to an input that is designated as EN (Enable). In this active mode, buffer  534  can drive information onto the NRZ lines for transmission to controller  200  or receive information from controller  200 . It is noted that all tri-state buffers described herein are functionally the same in providing for a tri-state high impedance mode and an active mode, via a control line. Similarly, serial data controller  114  includes an SD buffer  544  having a tri-state configuration so that a control line  542 , from data clock control section  500 , can select either the tri-state or active mode of operation. Buffer  544  is connected to a three line interface that is generally referred to as a serial servo data interface at least for the reason that the interface utilizes a serial data protocol. The lines which make up the serial servo data interface are labeled as they operationally pertain to serial data controller  544 , as well as SSD IN section  410  in controller  200  and include a servo clock, SC line, a servo out (SO)  1  line and a servo out (SO)  2  line, as indicated, these lines also appear entering SSD IN section  410 . It should be appreciated that SSD In section  410  does not require the use of a tri-state buffer for the reason that it only receives data. That is, the inputs to this section can be configured with a high impedance value. 
   As seen in  FIG. 2 , disk ports section  412  is diagrammatically illustrated by a dashed rectangle and includes a Controller Side (CS) Data Interface  560  having a tri-statable buffer section  562  that is connected to NRZ lines B 0 -B 7 , again as these lines pertain operationally to the NRZ bus. Buffer  562  can be selectively tri-stated using a buffer signal  564  that is originated from disk processor  400  and can readily be based on the servo gate, read gate and write gate signals that are generated by processor  400 . CS Data Interface  560  provides for bidirectional flow of NRZ data between the NRZ bus and a CS Data Section  566  using an eight bit wide connection  568 . Information that is stored in data section  566  can be processed, manipulated or moved in any suitable manner, for example, by disk processor  400  or by other portions of the drive such as for purposes of error correction. 
   Referring to  FIGS. 1-3 , details will now be provided with respect to the way in which user and servo data is communicated between channel  70  and controller  200 .  FIG. 3  is a flow diagram which illustrates one embodiment  600  for transferring servo data from channel  70  to controller  200 . For purposes of this example, it may be assumed that a write operation has just concluded, although identical steps may be applied following a read operation. At  602 , disk processor  400  sets write gate, WG, inactive. At  604 , processor  400  sets servo gate active. This causes mode control section  404  to set serial data control section  114  ( FIG. 2 ) into the servo data mode to prepare for receiving servo data and to cause data clock control section  500  to initiate clocking signals that are specific to the servo data mode. Read gate, RG, is set inactive at  606 . In this regard, it should be appreciated that an extended read gate signal can be used which allows read data to flow from the analog path and read path processing  550  which includes Viterbi  100  and ENDEC  102  of  FIG. 1 , since the servo data is processed essentially independently of the user read data. Further details will be provided below with respect to extended read gate. At  608 , Data Clock Control  500  and CS Clock Logic  502  cause buffers  534  and  562  at either end of NRZ bus lines to be tri-stated. It should be appreciated that the NRZ bus can remain tri-stated until a user data operation is initiated. That is, since there is a continuous need to process servo data, even in the absence of user data, it may be an expedient to tri-state the NRZ bus whenever no user data operations are occurring. Step  610  then activates or enables buffer  544  of serial data control section  114  such that the recovered servo clock, SC, can be driven onto the line so designated, as well as the B 4  line which normally serves in the transfer of user data. SO  1  and SO  2  are likewise driven onto lines designated as such as well as B 5  and B 6 , respectively, which normally serve in the transfer of user data. It should be appreciated that any arbitrary combination of lines can be selected on the user data bus, and there is no requirement to use B 4 -B 6 . At  612 , servo data can then be transferred, as needed. In the present example, this servo data is considered to be serial servo data or can be any suitable protocol that is different than the user data bus protocol. The servo clock, SC, controls clocking of the data while SO  1  and SO  2  serve to transfer what originated as serial data from the disk. While one conductor can be used for purposes of transferring the serial servo data, a two conductor parallel interface, as illustrated, can be used for carrying data such that the frequency of the SC signal is one half what would be necessary if only one data line were used. 
   During transfer of the serial data, NRZ bus  540  is transformed so as to operate using a limited subset of the overall number of NRZ lines and under a protocol that is unrelated to the operation of these specific lines during the transfer of NRZ user data. In this regard, as mentioned above, clocking signals for the NRZ data versus those required for the serial servo data are completely different from one another. The servo clocking remains relatively fixed in today&#39;s typical systems, although this is not a requirement in the application of the teachings that have been brought to light herein, while the NRZ clocking frequency varies with radial position on the disk. Further, there is no need to convert the serial servo data, including SC, from its native form to conform to an NRZ protocol for transfer to controller  200 . As discussed above, such data conversions can be quite complex, particularly with respect to clocking signals, and this conversion process requires additional logic and provides no particular value. With respect to this concern, two conversions are actually required as taught by the &#39;568 patent. The first conversion, on the channel side, transforms the servo data from its native protocol to NRZ protocol, while a second data conversion, on the controller side, transforms the servo data from NRZ protocol back to its native protocol. Using the concept brought to light herein, a considerable degree of flexibility has been provided. That is, any suitable subset of the NRZ lines can be transformed for use in implementing a different protocol on a time division multiplexed basis, while essentially eliminating constraints that are imposed by data conversion processes. 
   Having described the transfer of servo data immediately above, attention is now directed to  FIG. 4 , in conjunction with  FIGS. 1 and 2 . The former is a flow diagram which illustrates one suitable embodiment, generally indicated by the reference number  700 , for the transfer of user data between channel  70  and controller  200 . For purposes of this example, it may be assumed that a servo data operation has just concluded. At  702 , disk processor  400  sets servo gate, SG, inactive. At  704 , data clock control section  500  tri-states serial data buffer  544  responsive to mode control section  404  and its inputs as generated by disk processor  400  (see  FIG. 1 ). At  706 , disk processor  400  sets read gate, RG, or write gate, WG, active. Responsive to either RG or WG, data clock control section  500 , in  708 , enables buffer  534  of input/output latch  524 . In appropriate timed relation, disk processor  400  also enables CS buffer  562  of CS data interface  560  using line  564 . At  710 , user data can be transferred in either a user data read operation or a user data write operation. Optionally, at step  712 , the NRZ lines can be tri-stated upon completion of the user data transfer. As mentioned above, the NRZ lines can be tri-stated awaiting a user data transaction, since there may be no need to transfer user data between servo bursts, that are associated with adjacent servo wedges, in the absence of a user data operation. 
   While the foregoing descriptions are considered as providing an enabling disclosure,  FIG. 5  provides a timing diagram, generally indicated by the reference number  800 , which graphically further illustrates the concepts that have been described above with respect to operation of drive  10  and in view of  FIGS. 1 and 2 . Timing diagram  800  includes a servo burst trace  802  which illustrates a typical servo burst  804  including an AGC field, that is used to adjust gains, followed by a Sync or servo address mark. The latter is followed by a grey code which typically indicates track address, but can include more information. After the grey code, bursts A, B, C and D occur which are used in a well known manner for track following purposes. It should be appreciated, for purposes of control waveforms in  FIG. 5 , that active high signals have been illustrated. In this regard, active low signals can be used or any suitable mixture of active high and active low signals can be used. A servo gate (SG) trace  806  is illustrated, as produced by disk processor  400  of  FIGS. 1 and 2 . The servo gate signal can go active just before burst  804 . A servo clock (SC) trace  810  is illustrated, which represents the recovered servo clock, based on the servo burst and generally produced through the cooperation of servo and synthesizer section  80  and servo processing section  110  of  FIG. 1 . Information transmission by serial servo output data lines SO  1  and SO  2  is represented by traces  812  and  814 , respectively, in  FIG. 5 . A down-step  816  in each of these servo-related traces indicates the point at which control line  542  ( FIG. 2 ) caused buffer  544  to change from a tri-stated mode to an enabled mode. Conversely, after processing the servo data, the servo data related lines are again tri-stated, as indicated by an up-step  818  in each of traces  810 ,  812  and  814 . 
   Still referring to  FIGS. 1 ,  2  and  5 , a read gate signal trace  820  is illustrated, assuming that a user read operation, for an initial portion of the trace, is underway and approaching completion. Accordingly, read gate signal  820  goes inactive at  822 . Transfer of the user read data is synchronized by reference clock RC, as represented by a reference clock trace  824 . As seen in the servo data related traces  810 ,  812  and  814 , buffer  544  of serial data controller  114  ( FIG. 2 ) is tri-stated as NRZ user data is transferred in a first data transfer  826  of a first user read data trace  828 . At  830 , input/output latch buffer  534  and CS buffer  562  are tri-stated, in preparation for processing data relating to servo burst  804 , as described above. Read gate trace  820  illustrates an extended internal read gate signal  834 , that is represented by dashed lines, which provides for propagation of user read data through the analog path and associated components ahead of the servo data that is to follow. Thus, NRZ user data in first data transfer  826  is transferred almost up to enabling  816  of the servo clock line in trace  810  and the serial servo data lines in traces  812  and  814 . Servo data starts at  836  in traces SO 1  and SO 2 . The use of an extended internal read gate configuration provides for the use of additional space on the disk which would otherwise be unusable, due to constraints imposed by propagation delays. 
   A second data transfer  840  is illustrated using a second user read data trace  842 . This second user data transfer occurs subsequent to read gate trace  820  becoming active at  844 , while servo related traces  810 ,  812  and  814  are tri-stated. At  846 , buffer  534  of input/output latch  524  and CS buffer  562  are transitioned from a tri-state mode to an enabled or active mode. NRZ user read data is then transferred. 
     FIG. 5  further illustrates a user write data operation wherein a write gate trace  850  is initially active as a first user data write data operation  852  approaches completion. Responsive to completion of the first user data write operation, write gate trace  850  goes inactive at  854  which causes buffer  534  of input/output latch  524  ( FIG. 2 ) and CS buffer  562  to transition from active mode to the tri-state mode at  856 . In this regard, write gate does not extend beyond servo gate. A second user data write operation  860  is initiated responsive to write gate trace  850  going active at  862 , while servo related traces  810 ,  812  and  814  are tri-stated. It should be appreciated that the read and write operations that are illustrated by  FIG. 5  are not occurring simultaneously, but are each illustrated in timed relation to servo data related events. At  864 , buffer  534  of input/output latch  524  and CS buffer  562  are transitioned from the tri-state mode to the enabled or active mode. NRZ user write data  866  is then transferred. 
   Unlike prior art solutions such are exemplified by the &#39;568 patent, as discussed above, the configuration and method described herein provide for the transfer of servo data and user data in accordance with different protocols. In this way, data can be advantageously transferred in its native protocol with no need for translation or conversion into a different protocol and then re-conversion back to its native protocol. In order to accomplish these advantages, the interface between the channel and controller is transformed to operate in accordance with two or more different protocols at different times, as needed. Thus, each protocol can utilize its own clocking signals and combinations of data lines. 
   While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.

Technology Classification (CPC): 6