Abstract:
A method for performing Iddq testing including receiving an Iddq message and executing the Iddq message to measure current leakage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/416,641, filed Apr. 1, 2009, which is a divisional of U.S. application Ser. No. 10/694,730, filed Oct. 29, 2003, which claims the benefit of U.S. Provisional Application No. 60/421,780, filed Oct. 29, 2002, the contents of all of which are herein incorporated by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to serializer/deserializer integrated circuits with multiple high-speed data ports, and more particularly to a serializer and deserializer chip that includes the functionality to switch between multiple high-speed data ports. 
         [0004]    2. Related Art 
         [0005]    High-speed data links transmit data from one location to another over transmission lines. These data links can include serializer data links (i.e., SERDES) that receive data in a parallel format and convert the data to a serial format for high-speed transmission, and deserializer data links (i.e., SERDES) that receive data in a serial format and convert the data to a parallel format. SERDES data links can be used for communicating data through a backplane in a communications system (e.g., Tyco Backplane 16 or 30-inch trace). 
         [0006]    In a high-speed back plane configuration, it is often desirable to switch between multiple SERDES links. In other words, it is often desirable to switch between any one of multiple SERDES links to another SERDES link, and to do so in a low power configuration on a single integrated circuit. 
       SUMMARY OF THE INVENTION 
       [0007]    A multi-port SERDES transceiver includes multiple parallel ports and serial ports, and includes the flexibility to connect any one of the parallel ports to another parallel port or to a serial port, or both. Furthermore, the multi-port transceiver chip can connect any one of the serial ports to another serial port or to one of the parallel ports. Each parallel port and each serial port includes a plurality of input-output (IO) pads. According to embodiments of the present invention, the pads are programmable to support multiple different electrical specifications, data protocols, timing protocols, input-output functions, and the like. 
         [0008]    The IO pads for the parallel ports are programmable to support different data protocols, including, but not limited to, the XGMII protocol, the Ten Bit Interface (TBI) protocol, the Reduced TBI (RTBI) protocol, and the like. The IO pads are also programmable to support different electrical specifications, including, but not limited to, the High Speed Transistor Logic (HSTL) electrical specification, the Solid State Track Link (SSTL) electrical specification, the Low Voltage Transistor—Transistor Logic (LVTTL) specification, and the like. 
         [0009]    The multi-port transceiver of the present invention is also programmable to support multiple electrical specifications. The transceiver includes a plurality of management data input/output (MDIO) pads. Each MDIO pad is programmable to configure itself and its associated IO pads to comply with the appropriate electrical requirements and data protocols. The electrical specifications and data protocols include IEEE 802.3™ clause 45, IEEE 802.3™ clause 22, or the like. 
         [0010]    Depending on the specified electrical specification and the specified data protocol, the transceiver may be required to support different electrical requirements at the MDIO pad and the adjacent IO pads. Therefore, the MDIO pad is configured to have a separate power connection from the power connection to associated IO pads. In an embodiment, a split-voltage bus structure is provided to connect the pads for the transceiver to a bus. The structure breaks the power bus VDDO I/O supply, which allows the MDIO pads and the IO pads to operate at different voltage at a given time. 
         [0011]    The multi-port SERDES transceiver also includes a packet bit error rate tester (BERT). The packet BERT generates and processes packet test data that can be transmitted over any of the serial ports to perform bit error testing. The packet BERT can monitor (or “snoop”) between the serial ports. In other words, if data is being transmitted from one serial port to another serial port, the packet BERT can capture and store a portion of this data for bit error testing. 
         [0012]    The substrate layout of the multi-port SERDES transceiver chip is configured so that the parallel ports and the serial ports are on the outer perimeter of the substrate. A logic core is at the center of the substrate, where the logic core operates the serial and parallel data ports, and a bus that connects the data ports. The bus can be described as a “ring” structure (or donut “structure”) around the logic core, and is configured between the logic core and the data ports. The ring structure of the bus provides efficient communication between the logic core and the various data ports. 
         [0013]    Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
         [0014]    The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art(s) to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. 
           [0015]      FIG. 1  illustrates a multi-port SERDES transceiver chip according to an embodiment of the present invention. 
           [0016]      FIG. 2  illustrates a substrate layout of a multi-port SERDES transceiver chip according to an embodiment of the present invention. 
           [0017]      FIG. 3  illustrates sections of a bus on a multi-port SERDES transceiver chip according to an embodiment of the present invention. 
           [0018]      FIG. 4  illustrates path lengths of wires in a bus on a transceiver chip according to an embodiment of the present invention. 
           [0019]      FIG. 5  illustrates path lengths of wires in a bus on a transceiver chip according to another embodiment of the present invention. 
           [0020]      FIG. 6  illustrates a substrate layout of the multi-port SERDES transceiver chip according to another embodiment of the present invention. 
           [0021]      FIG. 7  illustrates a control system for programming a transceiver pad according to an embodiment of the present invention. 
           [0022]      FIG. 8  illustrates a pad timing controller according to an embodiment of the present invention. 
           [0023]      FIG. 9  illustrates a power bus connection for a multi-port SERDES transceiver chip according to an embodiment of the present invention. 
           [0024]      FIG. 10  illustrates an operational flow for configuring a transceiver pad to support a specified data protocol according to an embodiment of the present invention. 
           [0025]      FIG. 11  illustrates an operational flow for reconfiguring an output transceiver pad to function as an input according to an embodiment of the present invention. 
           [0026]      FIG. 12  illustrates an operational flow for programming a transceiver pad to perform Iddq testing according to an embodiment of the present invention. 
           [0027]      FIG. 13  illustrates an operational flow for changing a timing protocol for a transceiver pad according to an embodiment of the present invention. 
           [0028]      FIG. 14  illustrates an operational flow for configuring a transceiver pad to comply with a specified electrical specification according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]      FIG. 1  illustrates a multi-port SERDES transceiver  100  according to embodiments of the present invention. The SERDES transceiver  100  includes multiple parallel ports and serial ports, and includes the flexibility to connect any one of the parallel ports to another parallel port or to a serial port, or both. Furthermore, the multi-port transceiver chip  100  can connect any one of the serial ports to another serial port or to one of the parallel ports. 
         [0030]    More specifically, the SERDES transceiver chip  100  includes two parallel transceiver ports  102   a - 102   b  and four serial transceiver ports  104   a - 104   d.  Other configurations having a different number of ports could be used. The parallel transceiver ports  102   a - 102   b  transmit and receive data in a parallel format. The parallel transceiver ports  102   a - 102   b  can be XGMII parallel ports, for example, where the XGMII transceiver protocol is known to those skilled in the relevant art(s). Each XGMII port  102  can includes 72 pins, for example, operating at 1/10 the data rate of the serial ports  104 . 
         [0031]    The four serial ports  104   a - d  can be XAUI serial ports, and transmit and receive data in a serial format. Each serial port  104  can be a quad serial port having four serial data lines using the XAUI protocol that is known to those skilled in the relevant art(s). In embodiments of the invention, the serial ports  104  can operate at data rates of 3.125 GHz, 2.5 GHz, and 1.25 GHz. In other words, transceiver chip  100  is a multi-rate device. However, the XAUI data rates above are effectively quadrupled since there are four serial data lines in each serial port  104 . The serial ports  104  can be further described as a 10-Gigabit extension sub-layer (XGXS). In embodiments, the serial data ports  104  are differential. 
         [0032]    The parallel ports  102  and the serial ports  104  are linked together by a bus  106 . The bus  106  enables data to travel between all the ports  102  and  104 . More specifically, the bus  106  enables data to travel from one parallel port  102  to another parallel port  102 , and to travel from one parallel port  102  to a serial port  104 . Multiplexes  108  connect the bus  106  to the parallel ports  102  and to the serial ports  104 . The serial port  104  performs a parallel to serial conversion when receiving parallel data that is to be sent out serial. Likewise, the bus  106  enables data to travel from one serial port  104  to another serial port  104 , and to travel between a serial port  104  and a parallel port  102 . The parallel port  102  performs a serial-to-parallel conversion when receiving serial data that is to be sent out in parallel. The multi-port SERDES transceiver  100  is highly flexible in being able to connect multiple parallel ports  102  to multiple serial ports  104 , and vice versa. 
         [0033]    In embodiments, the SERDES transceiver chip  100  can be implemented on a single CMOS substrate. For example, the SERDES transceiver chip  100  can be implemented using a low power 0.13-micron CMOS process technology, which lends itself to higher levels of integration and application. 
         [0034]    The transceiver  100  enables dual unit operation, where one parallel port  102  is paired up with two of the serial ports  104 , and the other parallel port  102  is paired up with the other two serial ports  104 . For example, parallel port  102   a  can be paired with serial ports  104   a  and  104   b.  Likewise, the parallel port  102   b  can be paired with serial ports  104   c  and  104   d.  However, there is complete selectivity of the ports that are grouped together for dual unit operation. For example, parallel port  102   a  can be paired with either serial ports  104   a  and  104   b,  or serial ports  104   c  and  104   d.  In a backplane configuration, this provides flexibility to connect a parallel port to one or more serial ports for redundancy. 
         [0035]    The transceiver  100  also includes a packet bit error rate tester (BERT)  112 . The packet BERT  112  generates and processes packet test data that can be transmitted over any of the serial ports  104  or parallel ports  102  to perform bit error testing. Any type of packet data can be generated to perform the testing and at different data rates. For example, the packet BERT  112  can generate packet data that can be used to test the SERDES data link. As such, the packet BERT  112  provides a built-in self test for the SERDES data link. The packet BERT  112  generates test data that is sent over one or more of the serial ports  104  using the bus  106  to perform the bit error rate testing of the SERDES data link. Likewise, the packet BERT  112  can capture test data received over any one of the serial ports  104  or parallel ports  102  using the bus  106  for comparison with test data that was sent out. A bit error rate can then be determined based on this comparison. 
         [0036]    In one embodiment, the packet BERT  112  is RAM-based so that the test data is stored and compared in a RAM memory to perform the bit error rate test. In another embodiment, the packet BERT  112  is logic-based so that the test data is generated by a logic function, and transmitted across a SERDES link. Upon receipt back, the test data is re-generated by the logic packet BERT  112 , for comparison with the original test data that was sent over the SERDES data link. A RAM packet BERT  112  is more flexible than a logic packet BERT  112  because there is no limitation on the data that can be stored in the RAM packet BERT  112 . However, a logic packet BERT  112  is more efficient in terms of substrate area because a RAM occupies more area than a logic circuit. 
         [0037]    Since the packet BERT  112  shares the same bus  106  with the serial ports  104 , the packet BERT  112  can monitor (or “snoop”) between the serial ports  104 . In other words, if data is being transmitted from one serial port  104  to another serial port  104 , the packet BERT can capture and store a portion of this data for bit error testing. In one embodiment, the packet BERT  112  “blindly” captures data being sent from one serial port  104  to another serial port  104 . In another embodiment, the packet BERT  112  starts capturing data after a particular byte of data is transmitted. In another embodiment, the packet BERT  112  starts capturing data after an error event occurs. 
         [0038]    The SERDES transceiver chip  100  also includes the ability to include other optional logic blocks  114  that are not necessary for the operation of the SERDES transceiver. In other words, these could be customer-driven logic blocks or some other type of logic block. These optional logic blocks  114  can transmit and receive data over the serial ports  104  or parallel ports  102  using the bus  106 . The packet BERT  112  and the optional blocks  114  connect to the bus  106  using the multiplexers  110 . 
         [0039]    The SERDES transceiver chip  100  also includes a management interface  116  that enables the configuration of the portions (parallel ports  102 , serial port  104 , packet BERT  112 , and optional logic blocks  114 ) of the transceiver chip  100 . In an embodiment, the management interface  116  is configured to be compatible with both IEEE 802.3™ clause 45 and the IEEE 802.3™ clause 22 management standards. The management interface  116  includes two pads  117  that enable two different management chips to program and control the portions of the transceiver chip  100 . For example, one management chip connected to pad  117   a  could control the parallel port  102   a  and the serial ports  104   a  and  104   b,  and another management chip connected to pad  117   b  could control the parallel port  102   b  and the serial ports  104   c  and  104   d.  The quantity of pads  117  and management chips are provided for illustrative purposes. A greater or smaller quantity of pads  117  and management chips can be included as determined by the system designer. 
         [0040]      FIG. 2  illustrates the substrate layout  200  for the SERDES transceiver  100  according to embodiments of the present invention. The substrate layout  200  is configured to minimize the substrate area of the transceiver  100 , and efficiently provide the port interconnections described above. 
         [0041]    The substrate layout  200  is configured so that the parallel ports  102   a - 102   b  and the serial ports  104   a - 104   d  are on the outer perimeter of the substrate layout  200 , as shown. A logic core  202  is at the center of the substrate layout  200 , where the logic core  202  operates the bus  106 , serial ports  104 , and parallel  102  ports. The management interface  116 , the packet BERT  112 , and the optional logic blocks  114   a - 114   c  are adjacent to the logic core  202  as shown. The bus  106  can be described as a “ring” structure (or donut “structure”) around the logic core  202 , and placed in between the logic core  202  and the parallel ports  102  and serial ports  104  that occupy the parameter of the substrate layout  200 . Furthermore, the ring structure of the bus  106  also provides efficient communication between the logic core  202  and the various ports  102  and  104 . Furthermore, the ring structure of the bus  106  also provides efficient communication between the management interface  116 , the packet BERT  112 , the optional logic blocks  114 , and the various ports  102  and  104 . 
         [0042]    The bus  106  is illustrated as eight sections  106   a - 106   g  for ease of illustration. Each section provides an interlace to the respective ports  102  or  104  that are adjacent to the respective sections. 
         [0043]      FIG. 3  represents one of the eight sections  106   a - 106   g  of the bus  106  according to embodiments of the present invention. Each section of the bus  106  can be represented as two paths  308  and  310 . Data enters the bus  106  through a buffer  302  and proceeds to its destination along the path  308  and through the buffers  304 . Once on the bus  106 , data passes from one section to another section of the bus  106  using the path  310  and passing through the buffers  312 . The mux  306  represents data passing from the bus  106  to a functional block, such as a parallel port  102 , serial port  104 , or packet BERT  112 . The actual wires and buffers on the bus  106  are matched to minimize signal distortion. 
         [0044]    In embodiments, the data wires in the bus  106  are deposited on the substrate for substrate layout  200  in a particular fashion. Namely, a power or ground is placed between adjacent (or near by) data wires. Furthermore, adjacent data wires on the bus  106  are placed on two separate layers. Therefore, a power or ground will be above or below a data wire, and adjacent to a data wire. Therefore, two nearby data wires will not be located directly adjacent to one another, but instead will be positioned diagonally to each other, thereby reducing cross-talk. 
         [0045]      FIG. 4  further illustrates an example layout of the bus  106 . The wires  402  between parallel ports  102  and serial ports  104  are configured to have the same path lengths. In other words, wires  402   a - d  are deposited so as to have the same path length so as to reduce signal distortion. 
         [0046]      FIG. 5  illustrates another embodiment of the bus  106  in the substrate layout  200 . Whereas  FIG. 4  depicted only four wires  402   a - 402   d  for connecting one port ( 102  or  104 ) to an adjacent port ( 102  or  104 ),  FIG. 5  depicts a plurality of wires  402   a - 402   n  for connecting two adjacent ports ( 102  and  104 ). The total number of wires  402   a - 402   n  is determined by the design of the chip  100 . 
         [0047]    In an embodiment, multi-port SERDES transceiver  100  is programmable to support different data protocols, including, but not limited to, the XGMII protocol, the Ten Bit Interface (TBI) protocol, the Reduced TBI (RTBI) protocol, and the like. Transceiver  100  is also programmable to support different electrical specifications, including, but not limited to, the High Speed Transistor Logic (HSTL) electrical specification, the Solid State Track Link (SSTL) electrical specification, the Low Voltage Transistor—Transistor Logic (LVTTL) electrical specification, and the like. The present invention includes methodologies or techniques for sending control signals to configure the parallel ports  102   a - 102   b  to support a designated data protocol. This can be explained with reference to  FIG. 6 , which illustrates a substrate layout  600  for the SERDES transceiver  100  according to another embodiment of the present invention. Substrate layout  600  includes a plurality of pads  604   a - 604   d  that are part of the four serial ports  104   a - 104   d.  In other words, each serial port  104  includes a plurality of pads  604 . As shown, serial port  104   a  includes a plurality of pads  604   a.  Serial port  104   b  includes a plurality of pads  604   b.  Serial port  104   c  includes a plurality of pads  604   c.  Serial port  104   d  includes a plurality of pads  604   d.    
         [0048]    Substrate layout  600  also includes a plurality of pads  602   a - 602   d  representing two parallel ports  102   a - 102   b.  Pads  602   a - 602   b  are part of parallel port  102   a,  and pads  602   c - 602   d  are part of parallel port  102   b.  Pads  602   a  and pads  602   d  are input pads. As such, transceiver  100  receives data and control signals at input pads  602   a  and input pads  602   d.  Pads  602   b  and  602   c  are output pads that enable transceiver  100  to transmit data and control signals. In an embodiment, each group of pads  602  includes forty-four individual pads. Forty of the pads are dedicated to sending or receiving data signals, and four of the pads are dedicated to sending or receiving control signals (e.g., clock signals). The total quantity of pads can be increased or decreased as determined by the system designer. Likewise, the ratio of data-to-control pads can also be increased or decreased to meet system requirements as determined by the designer. 
         [0049]    Substrate layout  600  also includes a plurality of management data input/output (MDIO) pads  606   a - 606   d.  MDIO pads  606   a - 606   d  represent another embodiment of pads  117   a - 117   b,  which are described above with reference to  FIG. 1 . MDIO pads  606   a - 606   d  are programmable to configure pads  602   a - 602   d  and  604   a - 604   d  for compliance with a designated electrical specification and/or data protocol. The electrical specification and/or data protocol is configured via an external pull-up or pull-down resistor(s) at the designated control pad. The electrical specifications include IEEE 802.3™ clause 45, IEEE 802.3™ clause 22, or the like. As shown MDIO pads  606   a  control pads  602   a - 602   b,  MDIO pads  606   b  control pads  604   c - 604   d,  MDIO pads  606   c  control pads  602   c - 602   d,  and MDIO pads  606   d  control pads  604   a    604   b.  As discussed above with reference to  FIG. 1 , in an embodiment, MDIO pads  606  receive instructions from one or more management chips. These instructions are executed by the MDIO pads  606  to configure transceiver  100  and parallel ports  102   a - 102   b  to be compatible with the designated electrical specification. As discussed, in an embodiment, one management chip is provided to instruct all MDIO pads  606  and their associated IO pads  602  and/or  604 . In another embodiment, a distinct management chip is provided to instruct each MDIO pad  606  and its associated IO pads  602  and/or  604 . In another embodiment, a separate management chip is provided to instruct a subset of MDIO pads  606  and their associated IO pads  602  and/or  604 . 
         [0050]    The serial IO pads  604   a - 604   d,  parallel IO pads  602   a - 602   d,  and MDIO pads  606   a - 606   d  are positioned to provide rotational symmetry for substrate layout  600 . Therefore, if the transceiver  100  is rotated 180 degrees, the serial and parallel ports can be connected to another communications device without impeding the performance of transceiver  100 , or having to reconfigure either device. The symmetrical layout of the components also allows efficiencies to be gained when the transceiver is being connected. For instance, while wire-bonding the pads (i.e.,  604   a - 604   d,    602   a - 602   d,  and  606   a - 606   d ), a technician only needs to design or configure equipment to wire-bond half of the transceiver  100  since the other half would have identical dimensions. 
         [0051]    As discussed, the pads  602   a - 602   d  for the parallel ports  102   a - 102   b  are programmable to support multiple different standards, protocols, and/or functions.  FIG. 7  illustrates a block diagram for logic or circuitry for a control system  700  for programming each pad  602  according to an embodiment of the present invention. Control system  700  includes one or more programmable control registers  702 , a pad timing controller  704 , input controller  706 , output controller  708 , and configuration control logic  710 . Configuration control logic  710  is responsive to various control signals, which are executed to program pad  602  such that it is capable of supporting a designated protocol. Input controller  706  sends an input control signal  722  to configuration control logic  710  to program pad  602  to receive input. Output controller  708  sends an output control signal  724  to configuration control logic  710  to program pad  602  to send output. 
         [0052]    Control registers  702  includes five types of control signals for programming pad  602 . A system operator inputs these control signals, but in an embodiment, the control signals are supplied by a computer system (not shown). The five control signals include a reset message  712 , an Iddq message  714 , a power down message  716 , a pad type message  718 , and a delay select message  720 . 
         [0053]    A reset message  712  is released to instruct pad  602  to change its originally designated function (i.e., input or output). For example, if pad  602  is originally designated as an output pad, the pad  602  is reconfigured to operate as an input pad upon receipt of a reset message  712 . In  FIG. 7 , pad  602  is an output pad. Therefore, reset message  712  is only delivered to input controller  706  to enable pad  602  to switch to receiving input. 
         [0054]    An Iddq message  714  is released to implement Iddq testing to measure the quiescent supply current of transceiver  100 . When executed, Iddq message  714  places the path across a pad  602  in a quiescent state to measure the leakage current. As shown, Iddq message  714  is sent to input controller  706 , output controller  708 , and/or configuration control logic  710  for implementation. 
         [0055]    A power down message  714  is released to suspend the operations of portions of pad  602 . If power down message  714  is delivered to input controller  706 , pad  602  no longer receives input. If power down message is delivered to output controller  708 , pad  602  no longer outputs data or control messages. If power down message  714  is delivered to configuration control logic  710 , the muxing and timing operations of the control logic  710  are suspended. 
         [0056]    PAD type message  718  specifies the data protocol and electrical specification, and instructs configuration control logic  710  to implement the specified data protocol and electrical specification. As discussed, the data protocol includes the XGMII, TBI, RTBI protocols, and the like. The electrical specification includes HSTL, SSTL, and LVTTL electrical specifications, and the like. 
         [0057]    Delay select message  720  specifies the path delay for input and output. The parameter specified in the delay select message  720  enables the system operator, or the like, to adjust the delay between input and output at each pad  602  for better system performance. 
         [0058]    As discussed above, the present invention allows transceiver  100  to be programmed to support different data protocols. Referring to  FIG. 10 , flowchart  1000  represents the general operational flow for configuring a programmable pad  602  to support a designated data protocol, according to an embodiment of the present invention. 
         [0059]    The control flow of flowchart  1000  begins at step  1001  and passes immediately to step  1003 . At step  1003 , protocol instructions for a designated data protocol are specified. Referring back to  FIG. 7 , the specified protocol instructions are placed in programmable control registers  702 . 
         [0060]    At step  1006 , a control signal carrying the protocol instructions are released to program a pad  602 . Referring back to  FIG. 7 , the control signal is shown as PAD type message  718 , which is received by configuration control logic  710 . 
         [0061]    At step  1009 , the control signal (i.e., PAD type message  718 ) is executed to implement the specified data protocol. At step  1012 , an output control signal  724  or input control signal  722  is sent to configuration control logic  710  to instruct the programmable pad  602  to function as an output or input. At step  1015 , pad  602  transmits or receives in accordance with the specified data protocol. Afterwards, the control flow ends as indicated at step  1095 . 
         [0062]    Referring back to  FIG. 7 , pad  602  is programmed to function as an output. However, pad  602  can be reconfigured to function as an input. Referring to  FIG. 11 , flowchart  1100  provides an example of a general operational flow for reconfiguring an output programmable pad  602  to function as an input. 
         [0063]    The control flow of flowchart  1100  begins at step  1101  and passes immediately to step  1103 . At step  1103 , pad  602  is instructed to cease functioning as an output. Referring back to  FIG. 7 , power down message  716  is sent to output controller  708 , which as a result, stops sending output control signal  724 . 
         [0064]    At step  1106 , input operations are initiated at pad  602 . Referring back to  FIG. 7 , reset message  712  is sent to input controller  706  to initiate the operations. At step  1109 , input control signal  722  is sent to configuration control logic  710 . At step  1112 , configuration control logic  710  executes the input control signal  722  to configure pad  602  to start receiving input. Afterwards, the control flow ends as indicated at step  1195 . 
         [0065]    As discussed above, programmable control registers  702  also release an Iddq message  714  to implement Iddq testing. Referring to  FIG. 12 , flowchart  1200  provides an example of a general operational flow for programming pad  602  to perform Iddq testing. 
         [0066]    The control flow of flowchart  1200  begins at step  1201  and passes immediately to step  1203 . At step  1203 , Iddq message  714  is released to either input controller  706  or output controller  708 , depending on the I/O operations currently designated for pad  602 . At step  1206 , Iddq message  714  is also released to configuration control logic  710 , which programs pad  602  to measure leakage as previously discussed. Afterwards, the control flow ends as indicated at step  1295 . 
         [0067]    As shown, if pad  602  is operating as an input pad, pad timing controller  704  receives pad data  726  from pad  602 . The delay select message  720  instructs pad timing controller  704  to buffer the pad data  726  for a prescribed time period before sending the data to its destination as internal data  728 . The prescribed time period is substantially the same as the path delay at other pads  602 . 
         [0068]    Conversely, if pad  602  is operating as an output pad, pad timing controller  704  receives internal data  728  and buffers the data for a prescribed time period before enabling it to be output as pad data  726 . 
         [0069]      FIG. 8  represents the buffering process for implementing path delay according to an embodiment of the present invention. As shown, pad timing controller  704  includes a plurality of buffers  802   a - 802   n  and a multiplexer  804 . Data enters pad timing controller  704  and is delayed in one or more buffers  802   a - 802   n  for a prescribed time period. The incoming data can be pad data  726  received by pad  602 , or internal data  728  received from another portion of transceiver  100 . 
         [0070]    Each buffer  802   a - 802   n  delays the incoming data a fixed delay time. The delay time is fixed internally. In other words, the system designer specifies the delay time for the buffers during fabrication of transceiver  100 , and this value is not changed by the control registers  702  or a system operator. The data is sent to the next buffer  802   a - 802   n  unless multiplexer  804  opens the communications path to receive the data. The delay select message  720  determines when multiplexer  804  opens the communications path. The communications path can be opened prior to the data entering one of the buffers  802   a - 802   n,  or at any point after the data is released from one of the buffers  802   a - 802   n.  Therefore, the delay select message  720  enables the path delay to be increased or decreased by specifying the number of buffers  802   a - 802   n,  if any, that the data should traverse. Once the data is received by multiplexer  804 , the data is sent to its destination as pad data  726  or internal data  728 . 
         [0071]    Hence, the multi-port SERDES transceiver  100  includes the ability to change the timing of parallel ports  102  and serial ports  104 . This includes the ability to change the timing between the data and clock signals. In other words, the registers in the parallel ports  102  and serial ports  104  can be re-programmed to operate at different timing protocols. Referring to  FIG. 13 , flowchart  1300  provides an example of a general operational flow for changing the timing protocol for a pad  602 . 
         [0072]    The control flow of flowchart  1300  begins at step  1301  and passes immediately to step  1303 . At step  1303 , one or more parameters are input to adjust the path delay. Referring back to  FIG. 7 , the parameters are entered at programmable control registers  702 . 
         [0073]    At step  1306 , the delay parameters are communicated to PAD timing controller  704 . Referring back to  FIG. 7 , the delay parameters are encoded in delay select message  720 . 
         [0074]    At step  1309 , the delay parameters (i.e., delay select message  720 ) are executed to specify the total delay period for the path delay. As discussed with reference to  FIG. 8 , the total delay period is measured by the quantity of buffers  802   a - 802   n  that data must traverse before being received by multiplexer  804 . 
         [0075]    At step  1312 , data (i.e., PAD data  726  or internal data  728 ) is received, and at step  1315 , the data is delayed the specified total delay period. At step  1318 , the data is sent to its destination. Afterwards, the control flow ends as indicated at step  1395 . 
         [0076]    As discussed with reference to  FIG. 6 , each MDIO pad  606   a - 606   d  is programmable to configure itself to comply with a designated electrical standard, such as IEEE 802.3™ clause 22, IEEE 802.3™ clause 45, or the like. For instance, IEEE 802.3™ clause 22 specifies the access to management scheme, including data protocol and electrical requirements. 
         [0077]    Pads  602   a - 602   d  are programmable to support any combination of data protocols (e.g., XGMII, TBI, RTBI, etc.) and electrical specifications (e.g., HSTL, SSTL, LVTTL, etc.), and the electrical requirements are determined by the designated electrical specification. For example, the SSTL electrical specification requires pads  602   a - 602   d  to operate at 2.5 volts. The HSTL electrical specification requires pads  602   a - 602   d  to operate at 1.5 volts or 1.8 volts. The LVTTL electrical specification requires pads  602   a - 602   d  to operate at 2.5 volts or 3.3 volts. 
         [0078]    Notwithstanding the electrical requirements for pads  602   a - 602   d,  MDIO pads  606   a - 606   d  must operate at 1.2 volts to comply with IEEE 802.3™ clause 45. To comply with IEEE 802.3™ clause 22, MDIO pads  606   a - 606   d  must operate at 2.5 volts. Accordingly, MDIO pads  606   a - 606   d  are programmable to configure themselves and their associated pads  602   a - 602   d  to comply with the appropriate electrical requirements. For example, to comply with IEEE 802.3™ clause 45, the power connection to the MDIO pads (e.g., pads  606   c ) and their corresponding input and output pads (e.g.,  602   d  and  602   c ) must be broken to allow the MDIO pads to operate at 1.2 volts and the input/output pads to operate at 2.5 volts. To enable the split voltage requirement to be implemented, a split-voltage bus structure is provided to connect the pads for transceiver  100  to a bus. An embodiment of a split-voltage bus structure is illustrated in  FIG. 9 . 
         [0079]      FIG. 9  illustrates power supply connections for MDIO pads  606   c - 606   d  and output pads  602   c,  according to an embodiment of the present invention. The power supply connections include VDDO I/O supply  912 , VSSO I/O supply  914 , VSSC core supply  916 , and VDDC core supply  918 . MDIO pads  606   c - 606   d  are separated from output pads  602   c  by split voltage structure  902   a - 902   b.  Structure  902   a - 902   b  breaks the power bus VDDO I/O supply  912 , which allows different electrical requirements to be provided for MDIO pads  606   c - 606   d  and the adjacent output pads  602   c.  Hence, the power signals  904 , data signals  906 , clock signals  908 , and ground signals  910  for MDIO pads  606   c - 606   d  will not interfere with the electrical and data signals communicated from output pads  602   c.  The connection for the VSSO I/O supply  914 , VSSC core supply  916 , and VDDC core supply  918  is not broken by the structure  902   a - 902   b.    
         [0080]    Referring to  FIG. 14 , flowchart  1400  provides an example of a general operational flow for configuring a programmable pad (i.e., serial IO pads  604   a - 604   d,  parallel IO pads  602   a - 602   d,  and MDIO pads  606   a - 606   d ) to comply with a specified electrical standard, such as IEEE 802.3™ clause 22, IEEE 802.3™ clause 45, or the like. 
         [0081]    The control flow of flowchart  1400  begins at step  1401  and passes immediately to step  1403 . At step  1403 , MDIO instructions are accessed to identify the specified electrical specification (e.g., HHTL, SSTL, LVTTL, etc.). As discussed, the MDIO pad  606  must operate at a certain voltage, depending on the specified electrical specification. 
         [0082]    At step  1406 , the MDIO instructions are executed to configure the electrical requirements for the associated IO pads  602  and/or  604 . As discussed, the IO pads  602  and/or  604  may be required to operate at a different voltage than the MDIO pad  606 . 
         [0083]    Once the electrical requirements have been configured, the control passes to step  1409 . At step  1409 , data and control signals are sent or received at the MDIO pad  606  and IO pads  602  and/or  604  in accordance with the specified electrical specification. Afterwards, the control flow ends as indicated at step  1495 . 
       CONCLUSION 
       [0084]    Example embodiments of the methods, systems, and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such other embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.