Patent Publication Number: US-9851400-B1

Title: System on a chip serial communication interface method and apparatus

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present disclosure is a continuation of and claims priority to U.S. patent application Ser. No. 14/293,475, filed Jun. 2, 2014, now U.S. Pat. No. 9,268,661, issued Feb. 23, 2016, which is a continuation of and claims priority to U.S. patent application Ser. No. 14/072,620, filed Nov. 5, 2013, now U.S. Pat. No. 8,762,608, issued Jun. 24, 2014, which is a continuation of and claims priority to U.S. patent application Ser. No. 11/855,618, filed Sep. 14, 2007, which is a non-provisional application of U.S. Provisional Patent Application No. 60/829,724, filed Oct. 17, 2006, and U.S. Provisional Patent Application No. 60/825,659, filed Sep. 14, 2006, which are incorporated herein in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to the field of data processing and, in particular, to techniques for testing blocks of a system on a chip through a serial communication interface. 
     BACKGROUND 
     A typical storage system on a chip (SOC) device has many functional blocks, e.g., a read channel (RC) block, a hard disk controller (HDC) block; a processor block; and static random access memory block (SRAM). For testing the various blocks, the SOC may be programmed into various “personality” modes. When the SOC is programmed into a personality mode, the definition of digital pins change and the SOC behaves like a discrete device depending on the selected personality mode. In an RC-only mode, the definition of most of the digital pins is changed to pins defined for the RC interface (e.g., the Advanced Technology Attachment (ATA) pins for the normal mode are used as the RC non-return-to-zero (NRZ) pins). This is achieved by multiplexing the block level interface pins out to the SOC pins. While this technique may work for high pin count SOCs (e.g., parallel Advanced Technology Attachment (PATA) SOCs), it may present difficulties with respect to low pin count SOCs. 
     Current trends see the SOC pin count, and the driving capability of the pins themselves, reducing. For an enterprise class SOC, the RC inside can easily run at 2.5 gigahertz (GHz) (and faster for the future) and, therefore, the SOC pins need to be able to drive the complementary metal oxide semiconductor (CMOS) signals at approximately 250 megahertz (MHz). In low pin count SOCs, the interface pins are not capable of driving more than 50 MHz digital signals. Also, to provide for ten bits of NRZ data, at least twelve pins are needed, not counting the control interface. It is impractical for the low pin count SOC to spare so many pins. 
     SUMMARY OF THE INVENTION 
     In view of the challenges in the state of the art, embodiments of the invention are based on the technical problem of reducing the amount of electrical connections of a system on a chip (SOC) that are used for testing components of the SOC. An SOC, complementary interface, and test unit are provided as suitable to solve the problems upon which at least one embodiment of the invention is based. 
     More specifically, there is provided, a method in accordance with various embodiments, in an SOC having a control logic block, a processor block, and a serial communication interface, where the serial communication interface performs operations including receiving a parallel signal stream from a control logic block of the SOC, receiving a personality mode selection signal, and converting the parallel signal stream to a serial signal stream and transmitting the serial signal stream from the SOC based at least in part on the receiving of the personality mode selection signal. 
     In various embodiments where the control logic block includes a read channel block (RDC), the method may further include placing the SOC into a RDC-only personality mode, based at least in part on said receiving of the personality mode selection signal, to facilitate testing of the RDC. 
     In various embodiments the serial communication interface may perform the operation of transmitting the serial signal stream via a first serial port of the SOC, receiving a second serial signal stream via a second serial port of the SOC, converting the second serial signal stream to a second parallel signal stream, and transmitting the second parallel signal stream to the control logic block. The transmitting of the serial signal may include transmitting the serial signal stream via a pair of differential signal lines coupled to the first serial port. 
     Various embodiments may include SOCs that provide suitable solutions to at least some of the above identified challenges found in prior art SOCs. For example, an SOC of some embodiments may include a processor block, a control logic block, which may include an RDC and/or a hard disk controller block (HDC), to output a parallel signal stream, and a serial communication interface communicatively coupled to the control logic block and the processor block. The serial communication interface may receive the parallel signal stream, receive a personality mode selection signal, and convert the parallel signal stream to a serial signal stream and output the serial signal stream based at least in part on the personality mode selection signal. 
     In various embodiments, the SOC may comprise a non-return-to-zero (NRZ) bus communicatively coupled to the control logic block and the serial communication interface to transmit at least a portion of the first parallel signal stream from the control logic block to the serial communication interface. 
     In various embodiments, the serial communication interface may have an output serial port with a pair of differential electrical connections to output the serial signal stream. The serial communication interface may also have a parallel-to-serial block to convert the parallel signal stream to a serial signal stream. The parallel-to-serial block may include an encoder to encode the parallel signal stream and a transmit PHY block to modulate the encoded parallel signal stream as the serial signal stream for output via the output serial port. 
     The serial communication interface may have a input serial port with a pair of differential electrical connections to receive a serial signal stream. In these embodiments the serial communication interface may convert the received serial signal stream to a parallel signal stream, and transmit the parallel signal stream to the control logic block of the SOC. 
     In various embodiments, the serial communication interface may additionally receive a parallel signal stream from the processor block of the SOC, convert the processor block&#39;s parallel signal stream to serial signal stream and transmit the serial signal stream via the same output serial port used for transmitting the serial signal streams of the RDC and/or HDC. 
     The serial communication interface of the SOC of various embodiments may have means for receiving a parallel signal stream from the control logic, which may be the RDC and/or the HDC, means for receiving a personality mode selection signal, means for converting the parallel signal stream to a serial signal stream and transmitting the serial signal stream from the SOC based at least in part on said receiving of the personality mode selection signal. 
     In various embodiments, the serial communication interface may include means for placing the SOC into an RDC-only personality mode, based at least in part on said receiving of the personality mode selection signal, to facilitate testing of the RDC. 
     In various embodiments, the serial communication interface may include means for receiving a serial signal stream that originates from off the SOC, means for converting the received serial signal stream to a parallel signal stream, and means for transmitting the another parallel signal stream to the control logic block. 
     In various embodiments, a testing system for testing components of the SOC may also be described and claimed herein. This testing system may include a test unit to be communicatively coupled to an SOC. The test unit may include a controller to provide a personality mode selection signal to place the SOC into a selected personality mode for testing the control logic block of the SOC. 
     The testing system may also include a serial communication interface, external to the SOC, to be communicatively coupled to the SOC and to the test unit. The off-chip serial communication interface may transmit a plurality of signal streams between the SOC and the test unit through a serial interface provided to the SOC and a parallel interface provided to the test unit. 
     In various embodiments the off-chip serial communication interface may receive, from the SOC, a serial signal stream, convert the serial signal stream to a parallel signal stream, and transmit the parallel signal stream to the test unit via the parallel interface. The off-chip serial communication interface may additionally/alternatively receive, from the test unit, another parallel signal stream, convert the another parallel signal stream to another serial signal stream, and transmit the another serial signal stream to the SOC via the serial interface. 
     Other features that are considered as characteristic for embodiments of the present invention are set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which: 
         FIG. 1  illustrates a block diagram of a test system in accordance with various embodiments of the present invention; 
         FIG. 2  illustrates a flow diagram of a serialization operation in accordance with various embodiments of the present invention; 
         FIG. 3  illustrates a block diagram of a system on a chip in a read channel-only personality mode in accordance with various embodiments of the present invention; 
         FIG. 4  illustrates a block diagram of an off-chip interface and test unit in accordance with various embodiments of the present invention; 
         FIG. 5  illustrates a table of read channel interface signals in accordance with various embodiments of the present invention; 
         FIG. 6  illustrates another table of read channel interface signals in accordance with additional embodiments of the present invention; 
         FIG. 7  illustrates a block diagram of an on-chip interface in accordance with various embodiments of the present invention; and 
         FIG. 8  illustrates a block diagram of an off-chip interface in accordance with various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which are shown, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment, but they may. The phrase “A/B” means A or B. The phrase “A and/or B” means (A), (B), or (A and B). The phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C) or (A, B and C). The phrase “(A) B” means (A B) or (B), that is, A is optional. 
     “Circuitry,” as used in any embodiment herein, may comprise, for example, singly or in any combination, hardwired circuitry, programmable circuitry, state machine circuitry, and/or firmware that stores instructions executed by programmable circuitry. 
       FIG. 1  illustrates a block diagram of a test system  100  for testing a storage system-on-a-chip (SOC)  104  in accordance with various embodiments of the present invention. In some embodiments, the SOC  104  may have a serial communication interface  108  (hereinafter “interface  108 ”), an embedded processor block, e.g., processor  112 , a memory block, e.g., static random access memory (SRAM)  116 , and one or more control logic blocks, e.g., a read channel block (RDC)  120  and a hard disk controller block (HDC)  124 , which may be communicatively coupled to each other at least as shown. In particular, at least the processor  112 , the RDC  120 , and the HDC  124  may be communicatively coupled to the interface  108  to provide an off-chip test unit  128  (hereinafter “test unit  128 ”) communicative access to these blocks. The test unit  128  may be communicatively coupled to the SOC  104  through an off-chip serial communication interface  132  (hereinafter “interface  132 ”). 
     As briefly discussed above, it may be desirable to test the blocks of the SOC  104  for reasons such as, e.g., debugging, characterizing internal operations, etc. This testing may be performed by placing the SOC  104  into an appropriate personality mode by driving a mode input  136  as desired. The interface  108  may receive an indication of the desired personality mode as a personality mode selection signal (hereinafter “selection signal”) along the mode input  136 . The interface  108  may then operate in a manner consistent with the selected personality mode of the SOC  104 . 
     In various embodiments, the SOC  104  may be placed in a normal mode, a processor mode, an HDC mode, and/or an RDC-only mode. 
     The normal mode may be the mode of typical operation of the SOC  104  with all of the blocks functional. The other modes may be test modes designed for testing specific operating characteristics of the blocks of the SOC  104 . 
     The SOC  104  may be placed in the processor mode to provide processor trace data (e.g., recorded information related to the code executing on the processor  112 ) to the test unit  128 . In essence, the processor mode may simply provide the test unit  128  a window into the executing operations of the processor  112 , e.g., the code that is currently executing and the code that is in the pipeline. This information may be used by the test unit  128  for debugging and/or other diagnostic analysis. 
     The HDC mode may be a test mode where all of the blocks are functional except for the RDC  120 . In this mode, the interface  108  may communicatively couple the operative blocks of the SOC  104 , e.g., processor  112 , SRAM  116 , and HDC  124 , to an RDC that is external to the SOC  104 , e.g., on the test unit  128 . This may provide an opportunity to try different RDCs in conjunction with the operative blocks of the SOC  104 . 
     The RDC-only mode may be a test mode where the entire SOC  104  is powered down except for the RDC  120 . The interface  108  may communicatively couple the RDC  120  to blocks of the test unit  128 , e.g., an HDC, processor, and/or memory blocks, for testing. 
     The mode input  136  may allow for a selection signal, e.g. a two-bit selection signal, to be provided to the interface  108 . This selection signal may originate from a controller that is external to the SOC  104 , e.g., on the test unit  128 . In an embodiment, the selection signal and their corresponding modes may be as follows: 00b=normal mode; 01b=RDC-only mode; 10b=HDC mode; and 11b=processor mode. However, other embodiments may include other selection signals and/or other modes. 
     The interface  108  may receive the selection signal and communicatively couple the appropriate blocks of the SOC  104  to the interface  132  and, subsequently, the test unit  128 . In some embodiments, this selective communicative coupling may be facilitated through a multiplexor  138 . 
     The interface between the blocks of the SOC  104  and the test unit  128  while the SOC  104  is in either the HDC mode or the RDC-only mode may be bidirectional, thereby allowing information to flow into and out of the SOC  104 . While various embodiments described in further detail below may be directed towards interfacing the RDC  120  with the test unit  128 , other embodiments may include interfacing other control logic blocks, e.g., HDC  124 , to the test unit. 
     The RDC  120  may communicate with the interface  108  through a number of parallel signal lines. In an embodiment, the RDC  120  may be communicatively coupled to the interface  108  by a non-return-to-zero (NRZ) bus, which may run, e.g., up to 300 megahertz (MHz) and be ten bits wide. Additionally, various clock and control lines may also be connected between the RDC  120  and the interface  108 . The interface between the RDC  120  and the interface  108 , including the NRZ bus and other signal, clock, and/or control lines, may be referred to as a native RDC interface. 
     While the SOC  104  is in the RDC-only mode, the test unit  128  may be adapted to communicate with the RDC  120  through a complementary native RDC interface. However, providing such an interface with, e.g., 10 or more 300 MHz pads, on the SOC  104  may unduly limit the size of the SOC  104 . That is, the size of the SOC  104  needed to accommodate these electrical connections may be larger than the size needed for all of the logic on the SOC  104  providing the desired functionality. This is especially true as integrated circuit logic is becoming smaller and smaller (from 60 nanometer (nm) processes to 45 nm processes and beyond). If the size of the SOC  104  were pad-limited, the SOC  104  may have unused die space, which may sometimes be referred to as whitespace. 
     Accordingly, in an embodiment of the present invention, the interface  108  may include serialization and/or parallelization logic to allow for interface  108  to communicate with the test unit  128  via one or more serial ports, e.g., an output serial port  140  and an input serial port  144 , and the interface  132 . As will be shown in further detail below, the interface  132  may have parallelization and/or serialization logic to complement similar logic found in the interface  108 . 
     The serialization and/or parallelization logic of the interface  108  may be placed in what would otherwise be whitespace of the SOC  104 . Therefore, the size of the SOC  104  may be determined by the size of the logic to provide the desired functionality rather than the size of the electrical connections, thereby facilitating a reduction in cost and/or size of the SOC  104  without sacrificing performance. 
     Each of the output serial port  140  and the input serial port  144  may include electrical connections configured to couple to corresponding differential transmission lines, e.g., (TxA_P, TxA_N, TxB_P, and TxB_N) and (RxA_P, RxA_N, RxB_P, and RxB_N), respectively. The differential transmission lines may communicatively couple the SOC  104  to interface  132 , which may provide the test unit  128  with the native RDC interface. 
       FIG. 2  illustrates a flowchart depicting an output operation  200  of the interface  108  in accordance with an embodiment of this invention. In phase  204  the interface  108  may receive a parallel signal stream from one or more blocks to which it is communicatively coupled, e.g., the processor  112 , the RDC  120 , and/or the HDC  124 . In phase  208  the interface  108  may also receive a selection signal on the mode input  136 . Depending on the personality mode of the SOC  104 , determined by the received selection signal, the interface  108  may convert a parallel signal stream from one or more selected blocks to a serial signal stream in phase  212 . The interface  108  may then output the serial signal stream from the output serial port  140  in phase  216 . 
       FIG. 3  illustrates the SOC  104  in more detail in accordance with various embodiments of the present invention. The SOC  104 , as shown in this embodiment, may be in the RDC-only personality mode with only the RDC  120  active. In this embodiment, the interface  108  may include a parallel-to-serial (PAR2SER) block  304 , a serial-to-parallel (SER2PAR) block  308 , and a delay  312 , communicatively coupled to the RDC  120  as shown. 
       FIG. 4  illustrates the interface  132  and test unit  128  in more detail in accordance with various embodiments of the present invention. The interface  132  shown in  FIG. 4  may be configured to complement the interface  108  as shown in  FIG. 3 . In particular, the PAR2SER block  304  may be communicatively coupled to a complementary SER2PAR block  404  and the SER2PAR block  308  may be communicatively coupled to a complementary PAR2SER block  408 . The interface  108  may also include a delay  412 . The interactions of these components may be described in further detail below. 
     A listing and brief description of the signals to and/or from the RDC  120  as shown in  FIG. 3  may be found in table  500  of  FIG. 5  in accordance with various embodiments of the present invention. The table  500  lists the name, type, interface, and brief description of the various signals shown in  FIG. 3 . In some embodiments, e.g., if the RDC  120  is an enterprise class RDC, it may also have the signals given in table  600  of  FIG. 6 , in accordance with various embodiments of the present invention. 
     As shown in  FIG. 3 , the signal interfaces of the RDC  120  may be as follows: ANALOG signal interface  316 , DIG_RW signal interface  320 , DIG_MODE signal interface  324 , DIG_SERVO signal interface  328 , DIG_MISC signal interface  332 , and DIG_SIF signal interface  336 . 
     In various embodiments the ANALOG signals may be routed from/to the RDC  120  to/from various components, e.g., buffers, preamplifiers, positive emitter coupled logic (PECL), oscillators, etc. 
     In various embodiments, at least the reset signal of the DIG_MISC signals and the DIG_SIF signals may be input to the RDC  120  from the test unit  128  via relatively low-speed digital electrical connections on the SOC  104  (compared to the relatively high-speed analog electrical connections of the input and output serial ports). Furthermore, the OSC_CLK of the DIG_MISC signals, the DIG_MODE signals, and/or the DIG_SERVO signals may also be input and/or output via relatively low-speed digital electrical connections on the SOC  104 . However, instead of being routed directly between the test unit  128  and the RDC  120 , these signals may be routed through the delays of the respective interfaces as will be discussed in further detail below. 
     In various embodiments, the output DIG_RW signals may be output from the RDC  120  to the PAR2SER block  304 . These output DIG_RW signals may include a parallel signal stream having, e.g., signals from the read NRZ bus, error flags, and clock signals, provided to the interface  108 . With the SOC  104  in RDC-only mode, the interface  108  may multiplex these parallel signals to the PAR2SER block  304 , where the signals may be serialized into a serial signal stream for output along the transmission differential lines, e.g., Tx_P and Tx_N (the A pair and/or the B pair). The complementary SER2PAR block  404  may receive the serial signal stream transmitted over Tx_P and Tx_N, parallelize the signals, and provide the reconstituted output DIG_RW signals to the test unit  128  as the parallel signal stream of its native RDC interface. 
     In a similar but converse manner, the test unit  128  may transmit the input signals DIG_RW signals  320  to the PAR2SER block  408  for serialization and subsequent transmission via the reception differential lines, e.g., Rx_P and Rx_N (the A pair and/or the B pair). The complementary SER2PAR block  308  may parallelize the signals, and provide the reconstituted input DIG_RW signals to the RDC  120  as the parallel signal stream of its native RDC interface. 
     In various embodiments, the DIG_SERVO signals, which may include a servo data interface having two data lines and one line for clock signals, may be output from the RDC  120  to the interface  132 . The interface  132  may route the DIG_SERVO signals through delay  412 , which may be configured to delay the signals by an amount corresponding to the processing time of the signals passing through parallelization logic of the SER2PAR  404 . The DIG_SERVO signals  328  may then be provided to the test unit  128 . 
     In a similar but converse manner, the test unit  128  may provide DIG_MODE signals  324  to the interface  108 , where they are routed through the delay  312 . The delay  312  may be configured to delay the signals by an amount corresponding to the processing time of the signals passing through the parallelization logic of the SER2PAR block  308 . 
     In various embodiments, the serialization and parallelization logic of the interfaces  108  and  132  may communicate with complementary logic at a fixed frequency. Accordingly, in these embodiments, these blocks may include a phase-locked loop (PLL) programmed to the desired rate of transfer, e.g., 3 GHz. The PLLs may be programmed through using the DIG_SIF signals. 
       FIG. 7  illustrates the PAR2SER block  304  and the SER2PAR block  308  in more detail in accordance with various embodiments of the present invention. In particular, the serialization and parallelization circuitry may be shown in this figure with greater specificity in accordance with various embodiments. While the circuitry shown and described with reference to this embodiment is one example of circuitry to effectuate the embodiments of the invention discussed above, other circuitry may additionally/alternatively be employed. 
     The PAR2SER block  304  may receive the parallel signal stream from the interface  108 . A first stream including, e.g., read NRZ signals, error flag signals, a read clock, etc., may be directed into a buffer, e.g., first-in, first-out (FIFO) buffer  704 . The FIFO buffer  704  may transmit a sixteen-bit signal to an encoder  708 , which may be, e.g., a dual eight bit: ten-bit encoder, for encoding. Subsequent to encoding, the encoder  708  may transmit the resulting twenty-bit signal to a physical layer device (PHY)  712 , which may be, e.g., a six gigabits per second (Gbps) transmission PHY. The PHY  712  may modulate the signal to effect transmission of serial signal stream via the pair of differential output lines, e.g., TxA_P and TxA_N. The FIFO buffer  704  may also transmit a three-bit signal to an encoder  716 , which may be similar to encoder  708 . 
     A second stream including, e.g., a read SDATA signal, servo NRZ signals, control signals, servo data clock signal, etc., may be presented to a synchronizer  720  and another FIFO buffer  732  substantially as shown. The synchronizer  720  may provide a four-bit signal to the encoder  716  and the FIFO buffer  732  may provide a nine-bit signal to the encoder  716 . Subsequent to encoding, the encoder  716  may output a twenty-bit signal to a PHY  736 , which may be similar to PHY  712 . The PHY  736  may modulate the signals for transmission of a serial stream via a second pair of differential output lines, e.g., TxB_P and TxB_N. Note that this embodiment includes two pairs of differential output lines; however, other embodiments may have any number of pairs. 
     The local differential signaling scheme employed by the PHYs  712  and  736  in various embodiments may facilitate high speed signaling, e.g., in the 4-6 GHz range. This may avoid the prior art challenges of providing a digital electrical connection that is large enough to support the desired signaling frequency. 
     Referring now to  FIG. 8 , there is shown the SER2PAR block  404  and the PAR2SER block  408  in more detail in accordance with various embodiments of the present invention. In particular, the serialization and parallelization circuitry is shown in this figure with greater specificity and as a complement to the embodiment depicted in  FIG. 7 , in accordance with various embodiments of the present invention. 
     The SER2PAR block  404  may include PHYs  804  and  808  to complement PHYs  712  and  736 , respectively, and decoders  812  and  816  to complement encoders  708  and  716 , respectively. 
     In this embodiment, the PHY  804  may receive a first serial stream over the first pair of differential lines, TxA_P and TxA_N, demodulate the received signals and transmit a twenty-bit demodulated signal to the decoder  812 . The decoder  812  may then decode the signal and transmit the decoded sixteen-bit signal to a latch, e.g., D-type flip flops (DFLOPS)  820  that may be used to pipeline the signal to allow a full clock cycle for data leaving the SER2PAR unit  404 . 
     The PHY  808  may receive a second serial stream over the second pair of differential lines, TxB_P and TxB_N, demodulate the received signals and transmit a twenty-bit demodulated signal to the decoder  816 . The decoder  816  may decode the signal and transmit a decoded three-bit signal to DFLOPS  820  and a decoded thirteen-bit signal to DFLOPS  824 . The DFLOPS  820  and  824  may latch the signals back into a parallel format that provide the native RDC interface for the test unit  128 . 
     In various embodiments the PAR2SER block  408  may have circuitry such as a FIFO buffer  828 , an encoder  832 , and a PHY  836 , communicatively coupled to one another as shown to serialize a first stream of signals received in parallel from the test unit  128  and output the signals in a serial stream over a first pair of differential lines, e.g., RxA_P and RxA_N. 
     The PAR2SER block  408  may also have circuitry such as a synchronizer  840 , an encoder  844 , and a PHY  848 , communicatively coupled to one another as shown to serialize a second stream of signals received in parallel from the test unit  128  and output the signals in a serial stream over a second pair of differential lines, e.g., RxB_P and RxB_N. Again, while two pairs of differential lines are shown in this embodiment, other embodiments may have other numbers of pairs. 
     The components of the PAR2SER block  408  may be similar to like-name components of the PAR2SER block  304  described above. 
     Referring once again to  FIG. 7 , the SER2PAR block  308  may include PHYs  740  and  744  to complement PHYs  836  and  848 , respectively, and decoders  748  and  752  to complement encoders  832  and  844 , respectively. 
     In this embodiment, the PHY  740  may receive the first serial stream over the first pair of differential lines, RxA_P and RxA_N, demodulate the received signals, and transmit a twenty-bit demodulated signal to the decoder  748 . The decoder  748  may, subsequent to decoding the received signal, transmit a sixteen-bit decoded signal to a latch, e.g., DFLOPS  756 . The DFLOPS  756  may latch the signals back into the parallel format that provides the native RDC interface for the RDC  120 . 
     The parallelization of the second serial stream received via the second pair of differential lines, e.g., RxB_P and RxB_N, may be done through the PHY  744 , decoder  752 , and DFLOPS  760  in a manner similar to the parallelization of the first serial stream through the PHY  740 , decoder  748 , and DFLOPS  756 . 
     While  FIGS. 7 and 8  may illustrate certain signals, e.g., read gate (RG), servo gate (SG), and write gate (WG) signals, being directed through PAR2SER block  408  and SER2PAR block  308  other embodiments, e.g., those shown and discussed with reference to  FIGS. 3 and 4 , may have these and/or other signals being transmitted in parallel to the differential transmission lines. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art and others, that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the embodiment discussed herein. Therefore, it is manifested and intended that the invention be limited only by the claims and the equivalents thereof.