Abstract:
A system and method are disclosed for supporting 10 Gigabit digital serial communications. Many of the functional components and sublayers of a 10 Gigabit digital serial communications transceiver module are integrated into a single IC chip using the same CMOS technology throughout the single chip. The single chip includes a PMD transmit/receive CMOS sublayer, a PMD PCS CMOS sublayer, a XGXS PCS CMOS sublayer, and a XAUI transmit/receive CMOS sublayer. The single chip supports both 10 Gigabit Ethernet operation and 10 Gigabit Fiber Channel operation. The single chip interfaces to a MAC, an optical PMD, and non-volatile memory.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE 
     This is a continuation application of U.S. Ser. No. 13/489,750, filed Jun. 6, 2012, entitled “System and Method for Implementing a Single Chip having a Multiple sub-layer PHY”, which is hereby incorporated by reference in its entirety and which is a continuation application of U.S. Ser. No. 10/282,933, filed Oct. 29, 2002, now U.S. Pat. No. 8,230,114, entitled “System and Method for Implementing a Single Chip having a Multiple sub-layer PHY”, which is hereby incorporated by reference in its entirety and which makes reference to, claims priority to and claims the benefit of U.S. provisional patent application Ser. No. 60/402,097 filed on Aug. 7, 2002 and entitled “System and Method for Implementing a Single Chip having a Multiple Sub-Layer PHY.” 
     U.S. Pat. No. 6,424,194, U.S. application Ser. No. 09/540,243 filed on Mar. 31, 2000, U.S. Pat. No. 6,389,092, U.S. Pat. No. 6,340,899, U.S. application Ser. No. 09/919,636 filed on Jul. 31, 2001, U.S. application Ser. No. 09/860,284 filed on May 18, 2001, U.S. application Ser. No. 10/028,806 filed on Oct. 25, 2001, U.S. application Ser. No. 09/969,837 filed on Oct. 1, 2001, U.S. application Ser. No. 10/159,788 entitled “Phase Adjustment in High Speed CDR Using Current DAC” filed on May 30, 2002, and U.S. application Ser. No. 10/179,735 entitled “Universal Single-Ended Parallel Bus; fka, Using 1.8V Power Supply in 0.13 MM CMOS” filed on Jun. 21, 2002, are each incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate generally to a system and method corresponding to part of a physical layer (PHY) in a high-speed digital communications system, and more particularly to integrating many of the physical layer functions in a high-speed digital transceiver module. 
     High-speed digital communication networks over copper and optical fiber are used in many network communication and digital storage applications. Ethernet and Fibre Channel are two widely used communication protocols used today and continue to evolve to respond to the increasing need for higher bandwidth in digital communication systems. 
     The Open Systems Interconnection (OSI) model (ISO standard) was developed to establish standardization for linking heterogeneous computer and communication systems. The OSI model includes seven distinct functional layers including Layer 7: an application layer; Layer 6: a presentation layer; Layer 5: a session layer; Layer 4: a transport layer; Layer 3: a network layer; Layer 2: a data link layer; and Layer 1: a physical layer. Each OSI layer is responsible for establishing what is to be done at that layer of the network but not how to implement it. 
     Layers 1 to 4 handle network control and data transmission and reception. Layers 5 to 7 handle application issues. Specific functions of each layer may vary to a certain extent, depending on the exact requirements of a given protocol to be implemented for the layer. For example, the Ethernet protocol provides collision detection and carrier sensing in the data link layer. 
     The physical layer, Layer 1, is responsible for handling all electrical, optical, and mechanical requirements for interfacing to the communication media. The physical layer provides encoding and decoding, synchronization, clock data recovery, and transmission and reception of bit streams. Typically, high-speed electrical or optical transceivers are the hardware elements used to implement this layer. 
     As data rate and bandwidth requirements increase, 10 Gigabit data transmission rates are being developed and implemented in high-speed networks. There is much pressure to develop a 10 Gigabit physical layer for high-speed serial data applications. XENPAK (XAUI module specification) compatible transceivers for 10 G applications may be used for the 10 G physical layer. XPAK (second generation to XENPAK specification) compatible transceivers for 10 G applications may also be used for the 10 G physical layer. The specification IEEE P802.3ae draft 5 describes the physical layer requirements for 10 Gigabit Ethernet applications and is incorporated herein by reference in its entirety. The 10 Gigabit Fibre Channel standard draft describes the physical layer requirements for 10 Gigabit Fibre Channel applications. 
     An optical-based transceiver, for example, includes various functional components such as clock data recovery, clock multiplication, serialization/de-serialization, encoding/decoding, electrical/optical conversion, descrambling, media access control, controlling, and data storage. Many of the functional components are often implemented in separate IC chips. 
     In the physical layer, several sublayers are supported. As an example, for 10 Gigabit serial operation, some of the key sublayers include a PMD TX/RX (physical media dependent transmit and receive) sublayer, a PMD PCS (physical media dependent physical encoding) sublayer, a XGXS PCS (10 Gigabit media independent interface extender physical encoding) sublayer, and a XAUI TX/RX (10 Gigabit attachment unit interface transmit and receive) sublayer. 
       FIGS. 1-3  show typical implementations of the various sublayers. In  FIG. 1 , the XAUI TX/RX sublayer and the XGXS PCS sublayer are implemented in CMOS on a single chip. The PMD PCS sublayer and PMD TX/RX sublayer are implemented on a second chip where the PMD PCS sublayer is implemented in 0.18 micron CMOS technology and the PMD TX/RX sublayer is implemented in SiGe technology. An interface between the two chips is required such as a XGMII (10 Gb media independent interface). The different technologies of the different chips and within the second chip require different voltage levels and, therefore, additional level translation circuitry within the transceiver module and/or within the second chip. Also, the interface between the two chips adds additional complexity and extra power dissipation to the transceiver module. 
     In  FIG. 2 , the XAUI TX/RX sublayer and the XGXS PCS and PMD PCS sublayers are implemented on a single chip in CMOS technology. The PMD TX/RX sublayer is implemented on a second chip in SiGe technology. An interface between the two chips is required. The different technologies of the different chips require different voltage levels and, therefore, additional level translation circuitry within the transceiver module. Also, the interface between the two chips adds additional complexity and extra power dissipation to the transceiver module. 
     In  FIG. 3 , the XAUI TX/RX sublayer, and the XGXS PCS and PMD PCS sublayers are implemented on a single chip in 0.18 micron CMOS technology. Also, the PMD TX/RX sublayer is implemented on the same chip with SiGe technology. All four sublayers are implemented on a single chip but using a combination of different technologies. The different technologies require different voltage levels and, therefore, additional circuitry to perform level translation of voltages within the chip. Also, the mixture of different process technologies will add extra steps to the fabrication process which will increase cost. 
     Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     Certain embodiments of the present invention provide a method and system for supporting 10 Gigabit digital serial communications. Aspects of the present invention address one or more of the problems outlined above. It is desirable to combine many of the functional components and sublayers of a 10 Gigabit transceiver module into a single IC chip using the same technology throughout to reduce cost, power consumption, complexity, and noise and to enhance overall transceiver performance. 
     A system of the present invention includes a single-chip multi-sublayer PHY comprising a PMD transmit/receive CMOS sublayer, a PMD PCS CMOS sublayer, a XGXS PCS CMOS sublayer, and a XAUI transmit/receive CMOS sublayer using a single CMOS technology. The single-chip multi-sublayer PHY supports both 10 Gigabit Ethernet operation and 10 Gigabit Fibre Channel operation. 
     A method of the present invention provides for integrating a PMD transmit/receive CMOS sublayer, a PMD PCS CMOS sublayer, a XGXS PCS CMOS sublayer, and a XAUI transmit/receive CMOS sublayer into a single-chip multi-sublayer PHY using a single CMOS technology. Both 10 Gigabit Ethernet operation and 10 Gigabit Fibre Channel operation are supported by said integrating. 
     These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a first typical implementation of several physical layer sublayers in a transceiver module. 
         FIG. 2  is a schematic block diagram of a second typical implementation of several physical layer sublayers in a transceiver module. 
         FIG. 3  is a schematic block diagram of a third typical implementation of several physical layer sublayers in a transceiver module. 
         FIG. 4  is a schematic block diagram illustrating certain components of a 10 Gigabit transceiver module with a XAUI interface in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic block diagram of a single-chip multi-sublayer PHY used in the transceiver module of  FIG. 4  in accordance with an embodiment of the present invention. 
         FIG. 6  is a schematic block diagram of the single-chip multi-sublayer PHY of  FIG. 5  illustrating the various sublayers in accordance with an embodiment of the present invention. 
         FIG. 7  is a more detailed schematic block diagram of the single-chip multi-sublayer PHY of  FIG. 5  used in the transceiver module of  FIG. 4  in accordance with an embodiment of the present invention. 
         FIG. 8  is a schematic block diagram of the single-chip multi-sublayer PHY of  FIG. 5  illustrating a synchronous mode and an asynchronous mode in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The PMD TX/RX sublayer (physical media dependent transmit and receive sublayer) provides the electrical functionality for transmission and reception of 10 Gigabit serial data. The functionality includes clock multiplication and data serialization, clock data recovery and data de-serialization, signal amplification and equalization, and differential signal driving. 
     The PMD PCS sublayer (physical media dependent physical encoding sublayer) is responsible for coding data to be transmitted and decoding data to be received on the PMD side of the transceiver. The functionality includes 64B/66B synchronization, descrambling, and decoding, 64B/66B encoding and scrambling, data transitioning, multiplexing, and phase detecting. 
     The XGXS PCS sublayer (10 Gigabit media independent interface extender physical encoding sublayer) is responsible for coding data to be transmitted and decoding data to be received on the XAUI side of the transceiver. The functionality includes 8B/10B encoding, 8B/10B decoding, randomizing, and lane alignment. 
     The XAUI TX/RX sublayer (10 Gigabit attachment unit interface transmit and receive sublayer) provides the electrical functionality for transmission and reception of 3 Gigabit 4-channel serial data. The functionality includes clock multiplication and data serialization, clock data recovery and data de-serialization, signal amplification, and differential signal driving. 
       FIG. 4  is a schematic block diagram illustrating certain components of a Gigabit transceiver module  5  with a XAUI interface  15  in accordance with an embodiment of the present invention. The transceiver module  5  may, in one embodiment of the present invention, be compatible with the XENPAK optical module standard. The transceiver module  5  may, in one embodiment of the present invention, be compatible with the XPAK optical module standard. The transceiver module  5  includes, for example, a single-chip multi-sublayer PHY  10 , an optical PMD  30 , and an EEPROM  40 . 
     According to an embodiment of the present invention, a media access controller (MAC)  20  interfaces to the single-chip multi-sublayer PHY  10  through the XAUI transmit and receive interface  15 . In general, the MAC layer is one of two sublayers of the data link control layer and is concerned with sharing the physical connection to a network among several upper-level systems. The single-chip multi-sublayer PHY  10  interfaces to the optical PMD  30  through a PMD transmit and receive interface  17 . The MAC  20  also interfaces to the single-chip multi-sublayer PHY  10  through the serial MDIO (management data input/output) interface  16 . The single-chip multi-sublayer PHY  10  also interfaces to EEPROM  40  through a two-wire serial interface  19 . A separate XGMII (10 Gigabit media independent interface) is not needed. 
     The XAUI interface  15  includes 4 channels of 3 Gigabit serial data received by the single-chip multi-sublayer PHY  10  from the MAC  20  and 4 channels of 3 Gigabit serial data transmitted from the single-chip multi-sublayer PHY  10  to the MAC  20 . In an embodiment of the present invention, the MAC includes a XGXS sublayer interface and a reconciliation sublayer (RS) interface. In one embodiment of the present invention, for Ethernet operation, the 3 Gigabit data rate is actually 3.125 Gbps and for Fibre Channel operation, the 3 Gigabit data rate is actually 3.1875 Gbps. 
     The PMD interface  17  includes a 10 Gigabit serial transmit differential interface and a 10 Gigabit serial receive differential interface between the single-chip multi-sublayer PHY  10  and the optical PMD  30  in accordance with an embodiment of the present invention. In one embodiment of the present invention, for Ethernet operation, the 10 Gigabit data rate is actually 10.3125 Gbps and for Fibre Channel operation, the 10 Gigabit data rate is actually 10.5188 Gbps. 
       FIG. 5  is a schematic block diagram of the single-chip multi-sublayer PHY  10  used in the transceiver module  5  of  FIG. 4  in accordance with an embodiment of the present invention. The single-chip multi-sublayer PHY  10  includes a PMD transmit (TX) section  110 , a PMD receive (RX) section  120 , a digital core section  130 , a XAUI transmit (TX) section  140 , and a XAUI receive (RX) section  150 . 
     Referring to  FIG. 6 , the PMD TX section  110  and PMD RX section  120  form a 10 Gigabit PMD TX/RX sublayer  220  in accordance with an embodiment of the present invention. The XAUI TX section  140  and XAUI RX section  150  form a 3 Gigabit XAUI TX/RX sublayer  210  in accordance with an embodiment of the present invention. The digital core section  130  comprises a XGXS PCS sublayer  230  and PMD PCS sublayer  240  in accordance with an embodiment of the present invention. 
       FIG. 7  is a more detailed schematic block diagram of the single-chip multi-sublayer PHY  10  of  FIG. 5  used in the transceiver module  5  of  FIG. 4  in accordance with an embodiment of the present invention. The single-chip multi-sublayer PHY  10  comprises three main blocks including a transmit block  310 , a receive block  340 , and a management and control block  370  including management registers and control interface  372  and optics control and status  374 . Clock interfaces are provided for configuring the XAUI and PMD interfaces to asynchronous or independent asynchronous operations in accordance with an embodiment of the present invention. 
     The transmit block  310  collects 4-lane 3 Gigabit data at the XAUI receivers  150  and reformats the data for 10 Gigabit serial transmission at the PMD differential CML drivers  110  in accordance with an embodiment of the present invention. The PMD CMU (clock multiplier unit)/Serializer  316  in the PMD TX/RX sublayer  220  is phase-locked to an external reference clock  332 . Each XAUI receiver (one per lane) in the XAUI TX/RX sublayer  210  has an internal delayed-lock loop (DLL), in DLL &amp; Deserializer  318 , to synchronize the sampling clock to the incoming data. After synchronization, a 3 Gigabit sampling clock samples the data in the center of the data eye pattern. The phase relationship between the edge transitions of the data and those of the sampling clock are compared by a phase/frequency discriminator. Output pulses from the discriminator indicate the direction of phase corrections. The pulses are smoothed by a loop filter. The output of the loop filter controls the internal phase interpolators which generate the sampling clock. The XAUI CMU phase locked loop (PLL) within the XAUI TX/RX sublayer  210  generates the clocks for the internal DLL phase interpolations. 
     For each XAUI DLL of the DLL &amp; Deserializer  318  within the XAUI TX/RX sublayer  210 , the single-chip multi-sublayer PHY  10  contains a loss-of-signal (LOS) detect circuit which monitors for data present at the XAUI receiver inputs  312 . A minimum single-ended input signal swing is used for a valid lock condition. The status of each individual LOS detector is observable in an internal register of the single-chip  10 . 
     The XAUI serial inputs  312  to the XAUI TX/RX sublayer  210  are to be AC-coupled in accordance with an embodiment of the present invention. AC coupling prevents voltage drops across input devices of the single-chip  10  when the input signals are sourced from a higher operating voltage device. If DC coupling is used, care is exercised to guarantee that the input signals do not exceed VDD levels. Noise due to overshoot and undershoot transients are also to be accounted for. 
     Each XAUI serial data stream is de-serialized to a 10-bit word by a serial-to-parallel converter of the DLL &amp; Deserializer  318  within the XAUI TX/RX sublayer  210 . The DLL output clocks the serial-to-parallel converter. Under normal operation, the DLL recovers the clock from the data. If data is not present, the clock is recovered from the internal reference clock. The output is sent to the XGXS PCS sublayer  230  in the digital core  130 . 
     A sync acquisition sub-block (part of Sync Detect; Lane Sync; 8B/10B Decoder  320 ) in the XGXS PCS sublayer  230  within the digital core  130  performs code group synchronization on the incoming 10-bit bytes from the DLL &amp; Deserializer  318 . A two-stage 10-bit shift register is used to recognize the valid boundary of the /COMMA/(K28.5) code group. Once a single /COMMA/ is detected, the 8B/10B decoder (in Sync Detect; Lane Sync; 8B/10B Decoder  320 ) is enabled. Upon detection of four /COMMA/ code groups without any intervening invalid code group errors, Sync Acquisition is declared. 
     The 8B/10B decoder (in Sync Detect; Lane Sync; 8B/10B Decoder  320 ) performs illegal code checks, running disparity checks, invalid code checks, and miscellaneous decoding logic within the XGXS PCS sublayer  230 . Both an illegal code and a running disparity error may cause an invalid code which advances the invalid code counter for performance monitoring. The invalid code counter is cleared upon a read access. 
     Running disparity (RD) is the difference between the number of 1&#39;s and 0&#39;s in a block of data. RD is positive when there are more ones and negative when there are more zeros. Each encoded 10 bits must have a RD of 0, +2, or −2 to ensure a high bit transition density for reliable clock recovery. Additionally, the RD encoding is alternated for DC balancing (maintaining an equal number of 1&#39;s and 0&#39;s). When an invalid code is received, the decoder replaces it with an /E/ (error code) K30.7 and increments the invalid counter. If a legitimate /E/ is received, the decoder passes it to the PCS without incrementing the invalid counter. 
     At the beginning of lane alignment each of the four Lane Alignment FIFO write-pointers (of the Lane Alignment FIFOs  322  within the XGXS PCS sublayer  230 ) is enabled upon detection of an /A/ on its lane in accordance with an embodiment of the present invention. The FIFO&#39;s  322  common read-pointer is enabled when all four XAUI lanes have detected /A/. Once an /A/ is detected in one lane without /A/ detections in the other three lanes within a programmable window (skew budget), all FIFOs  322  are reset forcing the lane alignment to start over again. The Lane Alignment FIFOs  322  support lane skew compensation of up to 5 byte-clocks. The device allows the user to have the external  21  UI as specified in IEEE 802.3ae. 
     The PMD PCS sublayer  240  uses a transmission code to improve the transmission characteristics of information to be transferred across the link and to support transmission of control and data characters in accordance with an embodiment of the present invention. The 64B/66B encoding (defined by IEEE 802.2ae clause 49 for transmission code and performed by the 64B/66B Encoder/Scrambler  326 ) ensures that sufficient transitions are present in the PHY bit stream to make clock recovery possible at the receiver. 
     The TX gearbox  328  in the PMD PCS sublayer  240  is a buffer that converts 66-bit data to 64-bit data for more efficient serialization. The TX gearbox  328  receives 66-bit data from the 64B/66B Encoder/Scrambler  326  and a 2-bit sync from the Type Generator at 156.25 MHz. The TX gearbox  328  outputs 64-bit data at 322.265 MHz to the PMD CMU/Serializer  316  within the PMD TX/RX sublayer  220 . A register bank is employed which is accessed in a circular manner. 
     Data is read out of the TX gearbox  328  using an internally generated 322.265 MHz clock. The data is converted to a 10 Gigabit serial stream within PMD TX/RX sublayer  220  and driven off-chip. Bit  0  of frame  0  (LSB) is shifted out first. 
     The PMD CMU/Serializer  316  within the PMD TX/RX sublayer  220  has a PLL that generates the 10 Gigabit clock by multiplying the internal 156.25 MHz reference clock. 
     The single chip  10  includes a lock detect circuit, which monitors the frequency of the internal VCO. The lock detect status is observable in the Analog Transceiver Status Register  0 . Register bit P_LKDTCMU goes high when the PMD CMU PLL is locked. The CMU lock detect signal is also provided as an output status at the PCMULK pin  330 . 
     The CML serial outputs (PCOP/N and PDOP/N)  314  may be AC-coupled or DC-coupled. The CML outputs are powered at +1.8V. Certain pins provide power to PCOP/N and PDOP/N, respectively. These high-speed CML outputs comprise a differential pair designed to drive a 50Ω transmission line. The output driver is back terminated to 50Ω on-chip, providing snubbing of any reflections. 
     An optical enable output, controlled by the TXON discrete input or the Management Interface allows for the option to deactivate the optical transmitter in the optical PMD  30 . The polarity of PDIP/N  344  and PDOP/N  342  may be reversed to accommodate difficult printed circuit board (PCB) layouts. Each differential signal pair has its own polarity control bit in the PMD/Optics Digital Control Register. 
     The single-chip  10  complies with the jitter specifications proposed for 10-Gbps Ethernet equipment defined by IEEE 802.3ae. The reference clock characteristics adhere to the requirements in accordance with an embodiment of the present invention. 
     The receiver block  340  accepts 10 Gigabit serial PMD data and reformats the data for transmission on the 4-lane 3 Gigabit XAUI transmitters  362 . One of the 3 Gigabit CMU clocks in the XAUI TX/RX sublayer  210  is used to retime all four XAUI transmitters. The XAUI CMU  346  in the XAUI TX/RX sublayer  210  is phase-locked to an external reference clock. 
     The PMD clock and data recovery (CDR)/Deserializer  348  within the PMD TX/RX sublayer  220  generates a clock that is at the same frequency as the incoming data bit rate (10 Gigabit data rate) at the serial data inputs, PDIP/N  344 . The clock is phase-aligned by a PLL so that it samples the data in the center of the data eye pattern in accordance with an embodiment of the present invention. 
     The phase relationship between the edge transitions of the data and those of the generated clock are compared by a phase/frequency discriminator. Output pulses from the discriminator indicate the direction of phase corrections. 
     The output of the loop filter controls the frequency of the VCO, which generates the recovered clock. Frequency stability without incoming data is guaranteed by an internal reference clock that the PLL locks onto when data is lost. 
     The single-chip  10  includes a lock detect circuit that monitors the 10 Gigabit frequency of the internal VCO within the PMD TX/RX sublayer  220 . The frequency of the incoming data stream is within ±100 ppm of the 10 Gigabit data stream for the lock detector to declare signal lock. The lock detect status is observable in the Analog Transceiver Status Register  0 . P_LKDTCDR goes high when the PMD CDR/Deserializer  348  is locked to the incoming data. The CDR lock detect signal is also provided as an output status at the PCDRLK pin  348 A. 
     The single-chip  10  includes a loss-of-signal (LOS) detect circuit that monitors the integrity of the serial receiver data path in the PMD TX/RX sublayer  220 . A peak detector looks for a minimum amplitude swing. If the serial data input is not present, the LOS_P bit in the Analog Transceiver Status Register  0  is set to zero. 
     The CDR/Deserializer  348  attempts to lock to the reference clock when the signal is less than the minimum amplitude swing and the P-LOSB_SEL bit is set accordingly. The loss of signal (LOS) from a peak detector condition is also reflected at the PLOSB output signal pin  351 . 
     The OPRXLOS  376  input pin is used by the external optical receiver&#39;s LOS monitoring to indicate the loss-of-light condition. The OPRXLOS directly or combined with the peak detector logic described above could force the CDR/Deserializer  348  to lock to the reference clock. The OPRXLOS polarity is programmable with the OPINLVL control bit in the PHY Identifier Register or pin OPINLVL  378  in accordance with an embodiment of the present invention. 
     The PMD CML serial inputs (PDIP/N)  344  on the single-chip  10  may be AC-coupled. AC coupling prevents voltage drops across input devices of the single-chip  10  when the input signals are sourced from a higher operating voltage device. If DC coupling is used, care should be exercised to guarantee that the input signals do not exceed VDD levels. Noise due to overshoot and undershoot transients should be accounted for. 
     The PMD serial data stream is deserialized by a serial-to-parallel converter of CDR/Deserializer  348  in the PMD TX/RX sublayer  220 . The CDR output clocks the serial-to-parallel converter. Under normal operation, the CDR recovers the clock from the data. If data is not present, the clock is recovered from the internal reference clock. The output is sent to the RX Gearbox  350  within PMD PCS sublayer  240 . The RX Gearbox  350  performs an equivalent function (in reverse) as the TX Gearbox  328 . 
     A Frame Synchronizer (which is a part of the 64B/66B Synchronizer/Descrambler/Decoder  352  in the PMD PCS sublayer  240 ) searches for the 66-bit boundary of the frame data and obtains lock to 66-bit blocks using the sync header and outputs 66-bit blocks. The descrambler (which is also a part of the 64B/66B Synchronizer/Descrambler-/Decoder  352  in the PMD PCS sublayer  240 ) processes the payload to reverse the effect of the scrambler using the same polynomial. The receiver process decodes blocks according to IEEE 802.3ae clause 49. 
     The Randomizer  356  in XGXS PCS sublayer  230  reduces EMI during the interpacket gap (IPG). The resultant idle patterns at the XAUI transmitters would be a repetitive high-frequency signal due to the 8B/10B encoder  358 . The Randomizer  356  outputs random /A/K/R/ patterns in all for lanes during the IPG. The Randomizer  356  starts on the column containing the End-of-Packet byte, EOP (T), and ends on SOP (start-of-packet). The polynomial, 1+x 3 +x 7  is used by the Randomizer  356 . For example, refer to IEEE 802.3ae Draft 5.0. 
     The 8B/10B Encoder  358  within the XGXS PCS sublayer  230  converts a byte-wide data stream of random 1&#39;s and 0&#39;s into a 10-bit DC-balanced serial stream of 1&#39;s and 0&#39;s with a maximum run length of 6. The code provides sufficient bit transitions to ensure reliable clock recovery. 
     Data is read out of the 8B/10B Encoder  358  using an internally generated 312.0-MHz clock. The data is then converted to a 3 Gigabit serial stream by Serializer  360  within XAUI TX/RX sublayer  210  and driven off-chip. Bit  0  of frame  0  (LSB) is shifted out first and is mapped to “A” of the 8B/10B encoder in accordance with an embodiment of the present invention. 
     The XAUI CMU  346  within the XAUI TX/RX sublayer  210  has a PLL that generates the 3 Gigabit clock by multiplying the internal 156.25-MHz reference clock in accordance with an embodiment of the present invention. The single-chip  10  includes a lock detect circuit, which monitors the frequency of the internal VCO. The CMU lock detect bit goes high when the XAUI CMU PLL is locked. The lock detect status is in the Analog Transceiver Status Register  0 , bit  7 . 
     The XAUI serial outputs, X[A:D]OP/N  362 , may be AC-coupled. The CML outputs are powered at +1.2V. The high-speed XAUI outputs comprise a differential pair designated to drive a 50′Ω transmission line. The output driver is back terminated to 50′Ω on-chip, providing snubbing of any reflections. The output driver also has pre-emphasis capability to compensate for frequency selective attenuation of FR-4 traces to compensate for ISI (inter symbol interference). The option is controlled via the XAUI Pre-emphasis Controller Register in accordance with an embodiment of the present invention. 
     The single-chip XAUI transmit and receive block interfaces provide the option to reverse the lane order and/or the lane polarity. The option is controlled via the XAUI Digital Control Register. The XAUI I/O interface lane assignment package pins may be reversed to accommodate difficult PCB layouts. A lane flipper optionally performs a byte-wise flip of the internal 32-bit data. By default, lane A carries byte  0 , lane B carries byte  1 , lane C carries byte  2 , and lane D carries byte  3 . When the Lane Flipper is enabled, lane A carries byte  3 , lane B carries byte  2 , lane C carries byte  1 , and lane D carries byte  0 . Setting bits XAUI_TX_FLIP_B and XAUI_RX_FLIP_B in the Management Interface XAUI Digital Control Register to zero reverses the XAUI lane order in accordance with an embodiment of the present invention. 
     The XAUI I/O interface bit assignment (P to N) to package pins may be reversed to accommodate difficult PCB layouts. Assert bits XAUI_TZ_INV and XAUI_RX_INV in the Management Interface XAUI Digital Control Register to reverse the XAUI lane polarity. 
     The single-chip multi-sublayer PHY  10  supports asynchronous clocking mode operation of the XAUI and PMD interfaces. The local reference clock or external transmit VCXO may adhere to the IEEE specifications. 
     In the asynchronous mode, an elastic FIFO  354  is used that accommodates a frequency difference of up to 200 ppm between a recovered clock and a local reference clock. Both the RX and TX data paths  310  and  320  contain elastic FIFOs  354  and  324 . Idle columns of four bytes are inserted or deleted during the IPG (inter packet gap) once the distance between the elastic FIFO&#39;s read and write pointers exceed a threshold. In addition, a column of sequence orders may be deleted during the IPG once the distance between the elastic FIFO&#39;s read and write pointer exceed a threshold. The delete adjustments only occur on IPG streams that contain at least two columns of idles or sequence order sets. 
     Referring to  FIG. 8 , the single-chip  10  supports an asynchronous mode that uses an external reference clock  301  (or two external reference clocks  301  and  302 ) for the PMD transmitter  110  and XAUI transmitter  140  in accordance with an embodiment of the present invention. Therefore, the Elastic FIFOs  324  and  354  are enabled to accommodate frequency differences between the XAUI DLL clock and the PMD CMU clock (external reference clock) and the PMD CDR clock and the XAUI CMU clock (external reference clock). The asynchronous mode also supports an independent transmit path reference clock and a receive path reference clock. 
     Clock cleanup mode uses the external VCXO to clean up a noisy system clock provided for the asynchronous mode of operation. The transmit block phase detector locks to the external reference clock rather than the XAUI DLL clock. The cleanup PLL lock detect status is available in Analog Transceiver Status Register, bit  1 . 
     In the synchronous mode, a 156 MHz reference clock is derived within the single-chip  10  from the incoming 10 Gigabit data on the PMD side. Also, a 156 MHz reference clock is derived from the incoming 3 Gigabit data on the XAUI side. Clean-up PLL&#39;s  303  and  304  may be used (see  FIG. 8 ) to clean up any noise on the internally generated reference clocks.  FIG. 8  illustrates that the single-chip  10  may be switched between the asynchronous mode and the synchronous mode in accordance with an embodiment of the present invention. 
     In one embodiment of the present invention, all modes of the single-chip multi-sublayer PHY  10  are programmable, including synchronous mode, asynchronous mode, Ethernet mode, and Fibre Channel mode. The EEPROM  40  may be pre-programmed to power up the transceiver module  5  into certain modes. 
     In an embodiment of the present invention, the same single-chip  10  may be used for 10 Gigabit Ethernet applications and for 10 Gigabit Fibre Channel applications. In other words, a user may purchase a single chip and select a 10 Gigabit Ethernet configuration, a 10 Gigabit Fibre Channel configuration, or both. 
     The single-chip  10  supports the IEEE 802.3 Clause 45 Station Management Interface. A 1-bit shift register receives data from the MDIO pin  16  of  FIG. 4  ( 380  in  FIG. 7 ) on the rising edge of the MDC clock pin  18  of  FIG. 4  ( 380 A in  FIG. 7 ). The frame format begins with a preamble for clock synchronization followed by the start-of-frame sequence. The read or write op-code, PRTAD and DVEAD fields follow next. Three device types are supported by DVEAD:00001=PMA/PMD, 00011=PCS, or 00100=XGXS PHY. Depending on the read/write op-code, data is either received or transmitted by the single-chip  10 . Once the 16-bit data field is transferred, the MDIO signal  16  is returned to a high-impedance state (idle). 
     During idle, MDC  18  is not required to be active. A read operation configures the MDIO  16  as an output. A write operation configures the MDIO  16  as an input. Writes to an unsupported register address are ignored. The PRTAD field is configurable via the PRTAD pins. The MDIO interface  16  supports 1.2V operation in accordance with an embodiment of the present invention. 
     The single-chip  10  provides a 2-wire serial interface  19  ( 381 - 383  in  FIG. 7 ) that enables the system to access external nonvolatile memory devices through the MDIO interface  16 . The single-chip  10  2-wire serial interface  19  accesses the external devices through two dedicated interface signals, SDA (data)  383  and SCL (clock)  382 . 
     The nonvolatile memory  40  stores device configuration and optical-module data, such as module identification, transceiver capabilities, standard level of support, manufacture, and vendor information. The content is programmed into the EEPROM  40  by the module vendor at manufacture. The default data rate setting for 2-wire is 100 kHz. The 2-wire interface  19  supports up to 32 kilobytes of memory-accessing with burst read or write mode operations. The 2-wire interface  19  supports reads from the starting location of the last location written to incremented by 1. 
     A random read sets the address point to the desired location. The EEPROM address pointer may be set for the location to be read. The single-chip  10  does not support multi-Master Arbitration. The 2WENB signal  381  permits tristating the SDA  383  and SCL  382  outputs to allow other master devices access to the EEPROM  40 . A clock synchronizing mechanism is provided at the 2-wire interface  19  as a handshake means for the byte-level data transfers between the single-chip  10  and the EEPROM slave device  40 . 
     The slave is able to hold the SCL line low after reception and acknowledgment of a byte and forces the master (single-chip  10 ) into a wait state until the slave is ready for the next byte transfer. To accommodate the feature, the high period of the clock immediately following the acknowledge byte appears extended, even if the slave is immediately ready for the transfer of the next byte. 
     The single-chip  10  loads the first 256 bytes of EEPROM location (000-255) into a shadow memory on-chip at MDIO address locations at initialization through the 2-wire interface  19  in accordance with an embodiment of the present invention. After reset, the system should wait 50 ms before accessing the shadow memory for proper content read. Shadow memory is write-protected from certain address locations. The single-chip  10  is capable of loading its control register setting from the EEPROM after exiting from the reset state. 
     In accordance with an embodiment of the present invention, all sublayers of the single-chip multi-sublayer PHY  10  are implemented in 0.13 micron CMOS technology. 
     The various elements of the system and method may be combined or separated according to various embodiments of the present invention. 
     In summary, certain embodiments of the present invention afford an approach for integrating multiple sublayers of a PHY onto a single-chip in such that the single-chip supports both 10 Gigabit Ethernet and 10 Gigabit Fibre Channel operation in the same transceiver module. 
     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.