Abstract:
A test architecture accesses IP core test wrappers within an IC using a Link Instruction Register (LIR). An IEEE P1500 standard is in development for providing test access to these individual cores via a test structure called a wrapper. The wrapper resides at the boundary of the core and provides a way to test the core and the interconnections between cores. The test architecture enables each of the plural wrappers in the IC, including wrappers in cores embedded within other cores, with separate enable signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of prior application Ser. No. 13/234,217, filed Sep. 16, 2011, currently pending; 
         [0000]    Which was a divisional of application Ser. No. 13/028,606, filed Feb. 16, 2011, now U.S. Pat. No. 8,051,349, granted Nov. 1, 2011;
 
Which was a divisional of prior application Ser. No. 12/887,664, filed Sep. 22, 2010, now U.S. Pat. No. 7,913,135, granted Mar. 22, 2011;
 
Which was a divisional of prior application Ser. No. 12/403,791, filed Mar. 13, 2009, now U.S. Pat. No. 7,831,875, granted Nov. 9, 2010;
 
Which was a divisional of prior application Ser. No. 11/759,025, filed Jun. 6, 2007, now U.S. Pat. No. 7,525,305, granted Apr. 28, 2009;
 
Which was a divisional of prior application Ser. No. 11/096,399, filed Apr. 1, 2005, now U.S. Pat. No. 7,242,211, granted Jul. 10, 2007;
 
Which was a divisional of prior application Ser. No. 10/028,326, filed Dec. 21, 2001, now U.S. Pat. No. 6,877,122, granted Apr. 5, 2005;
 
which claims priority under 35 USC  119 ( e )(1) of Provisional Application No. 60/257,790, filed Dec. 22, 2000.
 
         [0002]    This patent is related to and incorporates by reference patent application Ser. No. 09/864,509 filed May 24, 2001, titled: 1149.1 Tap Linking Modules. 
     
    
     BACKGROUND OF THE DISCLOSURE 
       [0003]    1. Field of the Disclosure 
         [0004]    This Disclosure relates generally to testing intellectual property (IP) cores via a test structure called a wrapper. The wrapper resides at the boundary of a core and provides a way to test the core and interconnections between the cores. Particularly, the Disclosure relates to a test architecture for accessing wrappers within an integrated circuit. 
         [0005]    2. Description of Related Art 
         [0006]      FIG. 1  illustrates the test structure of a prior art wrapper  100 . The wrapper includes test interface signals  109 , an instruction register  105 , and set of data registers  106 - 108 . The instruction register is a register accessed by the test interface signals to load test instructions that control the operation of the wrapper, in particular the instructions control the selection of a data register and control the mode of operation of the selected data register. The selected data register may be accessed by the test interface to shift test data in and out of the wrapper. The set of data registers shown in  FIG. 1  includes; (1) an internal scan register  108  for testing the core circuitry, (2) a boundary scan register  107  for controlling the inputs and outputs of the core during testing, and (3) a bypass register  106  for bypassing the wrapper via a single bit. Any number of additional user defined data registers may be included in the set of data registers of the wrapper, such as data registers supporting core emulation and programming operations as described in the referenced patent application Ser. No. 09/864,509. 
         [0007]    The test interface  109  includes; (1) a clock signal for timing wrapper shift and test operations, (2) a shift signal for enabling data to be shifted through the wrapper from the serial input (SI) to the serial output (SO), (3) a capture signal for causing data to be captured into the instruction register or a selected data register, (4) an update signal for causing data to be output from the instruction register or a selected data register, (5) a reset signal for initializing the wrapper&#39;s instruction and data registers, and (6) a select signal for selecting data to be shifted through either the instruction register from SI to SO, or through a selected data register from SI to SO. 
         [0008]    In the example of  FIG. 1 , the test interface signals are simply gated, via AND gates (A), by the select signal to either allow them to be coupled to the instruction register or to the data registers. Other coupling methods may be used, but gating is used in this example. As can be seen, when select is high, gates  101  couple the test interface signals to the instruction register and the serial output of the instruction register is coupled to SO via multiplexer  103 . In this configuration, the instruction register may be shifted via SI and SO for instruction loading/unloading. When select is low, gates  102  couple the test interface signals to the data registers and the serial output of the selected data register, as determined by the instruction loaded in the instruction register, is coupled to SO via multiplexers  104  and  103 . In this configuration, the selected data register may be shifted via SI and SO for data loading/unloading. 
         [0009]    As one skilled in the art of testing will see, the IEEE P1500 wrapper architecture is similar to the IEEE 1149.1 boundary scan architecture. The main difference between the P1500 wrapper architecture and 1149.1 boundary scan architecture is that the P1500 wrapper architecture accesses the instruction and data registers using discrete test interface signals  109  rather than accessing the instruction and data registers using the 1149.1&#39;s test access port (TAP) state machine interface. Thus P1500 wrappers are free of 1149.1 TAP interfaces. 
         [0010]      FIG. 2  illustrates a core  201  equipped with the wrapper  100  of  FIG. 1 . The test interface signals  109  of  FIG. 2  are indicated as Control (CTL), and SI and SO are indicated as labeled in  FIG. 1 . As the name implies the wrapper simply wraps around the core to provide a test access mechanism local to the core&#39;s input/output boundary. The instruction register  105 , bypass register  106 , and boundary register  107  are part of the wrapper. The internal scan register  108  is part of the core circuitry that may be accessed via the wrapper for testing the core. 
         [0011]      FIG. 3  illustrates a prior art method of connecting three individual wrappers  307 - 309  of cores 1-3 onto a single scan chain arrangement  301 . The wrapper arrangement  301  will exist inside an IC. The serial inputs of the wrappers  307 - 309  are indicated as SI-1, SI-2, SI-3. The serial outputs of the wrappers  307 - 309  are indicated as SO-1-, SO-2, and SO-3. The test interface signals  109  are bussed to the CTL-1, CTL-2, and CTL-3 inputs of wrappers  307 - 309 . As seen in  FIG. 3 , the arrangement  301  scan chain passes serially through the wrappers  307 - 309  from SI  302  to SO  303 . In this arrangement, all wrappers  307 - 309  can be controlled to load instructions via the SI  302  and SO  303  scan path, or all wrappers  307 - 309  can be controlled to load data via the SI  302  and SO  303  scan path. Access to the SI  302 , SO  303 , and test interface signals  109  of the arrangement  301  is typically provided to tester external of the IC. 
         [0012]      FIG. 4  illustrates the wrapper design of  FIG. 1  being modified to include an enable/disable capability. The modification includes adding an enable signal  402  and adding circuitry  401  (i.e. the OR (O) gate, AND (A) gate, and an inverter), responsive to the enable signal  402  to cause the wrapper to either be enabled to respond to the test interface  109  or be disabled from responding to the test interface  109 . In this example, a low on enable  402  will disable the wrapper from responding to the test interface  109  and a high on enable  402  will enable the wrapper to respond to the test interface  109 . 
         [0013]      FIG. 5  illustrates an alternate method of enabling/disabling wrappers. In this example, it is assumed the wrapper design is fixed (hard) and cannot be modified, as could the wrapper design of  FIG. 4 . With a fixed wrapper design, the enabling/disabling capability must be external of the wrapper. In  FIG. 5 , gating circuitry  501  is inserted into the test interface  109  signal path to the wrapper and an enable signal  502  is added and connected to the gating circuitry to either enable the test interface signals  109  to be input to the wrapper or disable the test interface signals  109  from being input to the wrapper. In this example, a low on enable  502  will disable the wrapper from receiving the test interface signals and a high on enable  502  will enable the wrapper to receive the test interface signals. The use of wrapper enable signals, while not necessarily as shown in the examples of  FIGS. 4 and 5 , is known. 
         [0014]    The IEEE P1500 standard will define the connections to a wrapper test structure for an individual core of an IC. The standard leaves open the interconnection of the wrappers around multiple cores and the interconnection of wrappers around hierarchically arranged cores within cores. 
       SUMMARY OF THE DISCLOSURE 
       [0015]    In accordance with the disclosure, the serial data paths into and out of the IC and into and out of the wrappers are selectively connected through input linking circuitry and output linking circuitry. The input linking circuitry and output linking circuitry provide for selective serial connection of any one, plural, or all of the wrappers on the IC between the serial data input and serial data output. 
         [0016]    In a hierarchical arrangement of cores and their wrappers, the input and output linking circuitry provide for selective connection of the highest-level wrapper to be included in the selective serial connection. Additionally, the input and output linking circuitry provide for the selective connection of any one, plural or all of the lower level wrappers to be included in the serial connection. 
         [0017]    The disclosed circuits provide for the selective connection of the wrappers through use of control signals output from link instruction registers. The link instruction registers produce these control output signals in response to instructions that are shifted into the link instruction registers. The link instruction registers also include a bypass path so they do not affect the shifting of test data through the serial connection of the wrappers. 
         [0018]    In a hierarchical arrangement of wrappers on an IC, a single enable signal line may be available external of the IC for controlling the selective connection of the wrappers with a minimum number of control lines. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  illustrates a known core test wrapper. 
           [0020]      FIG. 2  illustrates a core with a known wrapper. 
           [0021]      FIG. 3  illustrates a serial connection of three known wrappers. 
           [0022]      FIG. 4  illustrates a wrapper with an internal enable circuit. 
           [0023]      FIG. 5  illustrates a wrapper with an external enable circuit. 
           [0024]      FIG. 6A  illustrates a test architecture according to the Disclosure 
           [0025]      FIG. 6B  illustrates input linking circuitry of the  FIG. 6A  test architecture. 
           [0026]      FIG. 6C  illustrates output linking circuitry of the  FIG. 6A  test architecture. 
           [0027]      FIG. 7  illustrates wrapper arrangements for the  FIG. 6A  test architecture. 
           [0028]      FIG. 8A  illustrates the  FIG. 6A  test architecture coupled to a Link Instruction Register (LIR) according to the Disclosure. 
           [0029]      FIG. 8B  illustrates a 3-bit Instruction Register of the LIR. 
           [0030]      FIG. 9  illustrates wrapper and LIR arrangements for the  FIG. 8A  test architecture. 
           [0031]      FIG. 10  illustrates a wrapped core containing wrapped cores A and B. 
           [0032]      FIG. 11  illustrates a test architecture for the wrappers of  FIG. 10 . 
           [0033]      FIG. 12  illustrates  FIG. 10  wrapper arrangements. 
           [0034]      FIG. 13  illustrates a test architecture embedded within another test architecture. 
           [0035]      FIG. 14  illustrates the hierarchical access of  FIG. 13  wrapper arrangements. 
           [0036]      FIG. 15  illustrates a test architecture including a LIR according to the Disclosure. 
           [0037]      FIG. 16  illustrates a test architecture containing the  FIG. 15  test architecture. 
           [0038]      FIG. 17  illustrates the hierarchical access of  FIG. 16  wrapper arrangements. 
           [0039]      FIG. 18  illustrates further embedding of test architectures according to the Disclosure. 
           [0040]      FIG. 19  illustrates an alternate LIR circuit example. 
           [0041]      FIG. 20  illustrates a serial connection of test architectures according to the Disclosure. 
           [0042]      FIG. 21  illustrates a bypass arrangement for test architectures. 
           [0043]      FIG. 22  illustrates example circuitry for enabling the  FIG. 21  bypass arrangement. 
           [0044]      FIG. 23  illustrates the use of data resynchronization circuits in the serial path between test architectures according to the Disclosure. 
           [0045]      FIG. 24  illustrate an example circuit for the  FIG. 23  data resynchronization circuits. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    The circuits and processes disclosed in this patent are used in manufacturing to test and ensure proper operation of the integrated circuit products before sale. The circuits and processes disclosed in this patent can also be used after the sale of the integrated circuit products to test and ensure the continued proper operation of the integrated circuit products and possibly to develop and test software products associated with the integrated circuit products. 
         [0047]      FIG. 6A  illustrates a preferred test architecture  601  for accessing the wrappers  307 - 308  of  FIG. 3 , according to the present Disclosure. In the test architecture  601 , wrappers  307 - 309  have been positioned between an input linking circuitry  602  block and an output linking circuitry  603  block, such that the wrapper serial inputs (SI-1, SI-2, SI-3) are output from the input linking circuitry  602  and the wrapper serial outputs (SO-1, SO-2, SO-3) are input to the output linking circuitry  603 . The wrapper serial outputs (SO-1, SO-2, SO-3) are also input to the input linking circuitry  602 . The input linking circuitry  602  receives a serial input SI  604  and the output linking circuitry  603  outputs a serial output  605 . The control inputs (CTL-1, CTL-2, CTL-3) of wrappers  307 - 309  are commonly connected to test interface CTL bus  109 . The input and output linking circuitry  602  and  603  receive control inputs from a wrapper Link bus  606 . The enable inputs (Enable-1,2,3) of wrappers  307 - 309  are provided by an Enable bus  607 . 
         [0048]      FIGS. 6B and 6C  illustrate example implementations of input linking circuitry  602  and output linking circuitry  603 , respectively. Input linking circuitry  602  of  FIG. 6B  comprises multiplexers  608 - 610  which provide selectable connections between the serial inputs (SI-1, SI-2, SI-3) of wrappers  307 - 309  and signals SI  604 , SO-1, SO-2, and SO-3. Multiplexers  608 - 610  receive linking control (SELSI-1, SELSI-2, SELSI-3) inputs from Link bus  606 . The link control inputs  606  to multiplexer  610  enable the SI-3 serial input to wrapper  309  to be connected to SI, SI-1, or SI-2. The link control inputs  606  to multiplexer  609  enable the SI-2 serial input to wrapper  308  to be connected to SI, SI-1, or SI-3. The link control inputs  606  to multiplexer  608  enable the SI-1 serial input to wrapper  307  to be connected to SI, SI-2, or SI-3. Output linking circuitry  603  of  FIG. 6C  comprises multiplexer  611  which, in response to link control inputs from Link bus  606 , allows connecting either the SO-1 output of wrapper  307 , the SO-2 output of wrapper  308 , or the SO-3 output of wrappers  309  to SO  605 . 
         [0049]      FIG. 7  illustrates the various wrapper arrangements  7001 - 7007  possible between the SI  604  and SO  605  of test architecture  601 . These wrapper arrangements are formed by inputting link controls to input and output circuitry  602  and  603  via Link bus  606 , and by inputting enable controls to wrappers  307 - 308  via Enable bus  607 . Arrangement  7001  contains only wrapper  307  between SI and SO. Arrangement  7002  contains wrappers  307  and  308  in series between SI and SO. Arrangement  7003  contains wrappers  307  and  309  in series between SI and SO. Arrangement  7004  contains wrappers  307 ,  308 , and  309  in series between SI and SO. Arrangement  7005  contains wrapper  308  between SI and SO. Arrangement  7006  contains wrappers  308  and  309  in series between SI and SO. Arrangement  7007  contains wrapper  309  between SI and SO. 
         [0050]    As can be seen in  FIG. 7 , the test architecture  601  allows for the wrapper arrangement  301  of  FIG. 3  as well as many different wrapper arrangements. The Link  606  and Enable  607  inputs to test architecture  601  may come from IC pads or from circuitry within the IC, such as an IEEE 1149.1 Test Access Port circuit. While IC pads or Test Access Port circuits may provide the Link and Enable inputs, a preferred method of providing the Link and Enable inputs to the test architecture  601  is described in detail below. 
         [0051]      FIG. 8A  illustrates circuitry for providing the Link  606  and Enable  607  control inputs to test architecture  601 , according to the present Disclosure. The circuitry includes a Link Instruction Register (LIR)  801  in series with the test architecture  601 . The LIR  801  has a serial input  802  connected to SO  605  of the test architecture  601 , a serial output (SO)  803 , control inputs connected to test interface control bus  109 , and control outputs  804  connected to the Link  606  and Enable  607  inputs of test architecture  601 . The LIR  801  consists of 3-bit instruction register (IR)  805 , a multiplexer  806 , and gating circuitry  807 . 
         [0052]    During instruction scan operations, the select signal  808  of control bus  109  is high to enable the gating circuitry  807  to pass the control signals  109  to the 3-bit IR  805  and to connect the serial output of IR  805  to SO  803  via multiplexer  806 . In the instruction scan mode, the 3-bit IR  805  shifts instruction data when the test architecture shifts instruction data. Thus, during instruction scan operations, the 3-bit IR  805  becomes part of the instruction scan path between SI  604  and SO  803 . 
         [0053]    During data scan operations, the select signal  808  of control bus  109  is low to disable the gating circuitry  807  from passing control signals  109  to the 3-bit IR  805  and to connect SO  605  of test architecture  601  to SO  803  via multiplexer  806 . In the data scan mode, the 3-bit IR  805  is disabled and the LIR simply forms a bypass connection between the SO  605  of test architecture  601  and the SO  803  of the LIR. Thus, during data scan operations, the LIR is included in the data scan path between SI  604  and SO  803 , but it does not add to the bit length of the data scan path. Also, since the control bus  109  is gated off during data scan operations, the data contained in the LIR&#39;s IR  805  cannot be changed during data scan operations. 
         [0054]    It should be noted that while the LIR  801  has been shown inserted in the serial output path from the test architecture  601  (i.e. LIR input  802  connected to test architecture SO output  605 ), it could be have been similarly inserted in the serial input path to the test architecture  601  as well (i.e. LIR output  803  connected to test architecture SI input  604 ). Thus the position of the LIR  801  with respect to it being positioned at the beginning or ending of the serial path through the test architecture does not impact its ability to provide control of the Link  606  and Enable  607  bus inputs to the test architecture  601 . 
         [0055]      FIG. 8B  illustrates that the circuitry of the 3-bit IR  805  consists of a 3-bit shift register  810 , a 3-bit update register  811 , and decode logic  812 . During the shift step of an instruction scan operation, the 3-bit shift register  810  shifts data from its serial input to its serial output. During the update step of an instruction scan operation the data shifted into the 3-bit shift register  810  is transferred to the 3-bit update register  811 . The 3-bit update register outputs this data to decode logic  812 . The outputs of decode logic  812  respond to the data input from the 3-bit update register to output Link  606  and Enable  607  control signals to test architecture  601  via bus  804 . Reset signal  809  of control bus  109  is used to initialize shift register  810  and update register  811 , such that bus  804  may be set to a desired Link and Enable input state to test architecture  601 . While the examples of  FIGS. 8A and 8B  use a 3-bit IR, the IR could be of any bit length. The use of a 3-bit IR will be seen to be sufficient in selecting the wrapper arrangements described in regard to  FIG. 9  below. 
         [0056]      FIG. 9  illustrates the various wrapper arrangements  9001 - 9007  between SI  604  and SO  803  in response to different 3-bit codes scanned into LIR  801 . When the reset signal  809  is activated, the instruction registers  105  of wrappers  307 - 309  are initialized to a first instruction that selects the bypass registers  106  of the wrappers and enables normal operation of their associated cores. Also in response to the reset signal  809 , LIR  801  is initialized to contain all zeros, i.e. LIR=000. 
         [0057]    As seen in arrangement  9001 , when the LIR contains a 000 code following a reset or an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrapper  307  in the scan path between SI  604  and SO  803 . The other wrappers  308 - 309  are disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0058]    As seen in arrangement  9002 , when the LIR contains a 001 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrappers  307  and  308  in the scan path between SI  604  and SO  803 . Wrapper  309  is disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0059]    As seen in arrangement  9003 , when the LIR contains a 010 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrappers  307  and  309  in the scan path between SI  604  and SO  803 . Wrapper  308  is disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0060]    As seen in arrangement  9004 , when the LIR contains a 011 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrappers  307 - 309  in the scan path between SI  604  and SO  803 . 
         [0061]    As seen in arrangement  9005 , when the LIR contains a 100 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrapper  308  in the scan path between SI  604  and SO  803 . The other wrappers  307  and  309  are disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0062]    As seen in arrangement  9006 , when the LIR contains a 101 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrappers  308  and  309  in the scan path between SI  604  and SO  803 . Wrapper  307  is disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0063]    As seen in arrangement  9007 , when the LIR contains a 110 code following an instruction scan operation it outputs Link  606  and Enable  607  control to enable and connect wrapper  309  in the scan path between SI  604  and SO  803 . The other wrappers  307  and  308  are disabled and disconnected from the scan path between SI  604  and SO  803 . 
         [0064]    In all arrangements  9001 - 9007 , instruction scan operations shift data through the 3-bit IR  805  of LIR  801 , but data scan operations do not shift data through the 3-bit IR  805  of LIR  801 , as previously described. A current arrangement  9001 - 9007  will be maintained following an instruction scan operation as long as the 3-bit LIR code is not changed by the instruction scan operation. 
         [0065]    Some advantages of using the LIR  801  to control the Link  606  and Enable  607  inputs to the test architecture  601  are listed below. 
         [0066]    The LIR  801  exists and operates within the scan path of each selected wrapper arrangement  9001 - 9007 . Therefore no additional circuitry and/or interfaces (for example no 1149.1 Test Access Port and/or IC interface pads as mentioned in regard to  FIG. 7 ) are required to control the Link  606  and Enable  607  buses to switch between wrapper arrangements. 
         [0067]    The LIR  801  provides the opportunity of switching between wrapper arrangements  9001 - 9007  following each instruction scan operation. Thus the shifting in and updating of LIR wrapper arrangement codes and wrapper test instructions may be performed during the same instruction scan operation. 
         [0068]    The LIR  801  does not add bits to a selected wrapper arrangement  9001 - 9007  during data scan operations. By not adding to the bit length of a given wrapper arrangement, the test patterns applied to the wrapper arrangement do not have to be modified to accommodate the presence of the LIR. For example, if a test pattern set existed for testing core 1 using the internal scan register  108  ( FIG. 1 ) of wrapper  307 , arrangement  9001  could be selected via an instruction scan operation then the test patterns could be applied using data scan operations. Since the LIR does not add bits to the length of arrangement  9001  during data scan operations, the core 1 test pattern set can be applied without modification, enabling core 1 test pattern reuse 
         [0069]      FIG. 10  illustrates an example of a core 4  1001  which has a wrapper  1002 . Core 4 differs from the previously described cores 1-3 in that it contains an embedded core A  1003  having a wrapper  1004  and an embedded core B  1005  having a wrapper  1006 . Access to wrapper  1002  is provided via SI-4, SO-4, CTL-4, and Enable-4. Access to wrapper  1004  is provided via SI-A, SO-A, CTL-A, and Enable-A. Access to wrapper  1006  is provided via SI-B, SO-B, CTL-B, and Enable-B. 
         [0070]      FIG. 11  illustrates the test architecture  1101  of the present Disclosure being used to provide access to wrappers  1002 ,  1004 , and  1006  of core  4 . The test architecture is similar to the test architecture  601  described in regard to  FIG. 6  with the exceptions that; (1) wrapper  1002  has been substituted for wrapper  307 , (2) wrapper  1004  has been substituted for wrapper  308 , (3) and wrapper  1006  has been substituted for wrapper  309 . 
         [0071]      FIG. 12  illustrates the wrapper arrangements  1201 - 1207  selectable via the Link  606  and Enable  607  buses of test architecture  1101 . The wrapper arrangements  1201 - 1207  are the same as wrapper arrangements  7001 - 7007  of  FIG. 7  with the exceptions that; (1) wrapper  1002  has been substituted for wrapper  307 , (2) wrapper  1004  has been substituted for wrapper  308 , (3) and wrapper  1006  has been substituted for wrapper  309 . 
         [0072]      FIG. 13  illustrate a test architecture  1301  of the present Disclosure which contains wrapper  307 , wrapper  308 , and the test architecture  1101  of  FIG. 11 . Test architecture  1301  is similar to the test architecture  601  of  FIG. 6  with the exception that test architecture  1101  has been substituted for the core  3  wrapper  309 . Test architecture  1301  is serially connected to an N-bit LIR  1302  which provides control input via bus  1303  to the Link  606  and Enable  607  buses of test architecture  1301  and to the Link and Enable buses  1306  of test architecture  1101 , as described previously in regard to the 3-bit LIR  810  of  FIG. 8A . The N-bit LIR  1302  is similar to the 3-bit LIR  810  except that its IR contains addition bits for decoding the additional Link and Enable-4, A, B signals  1306  required by test architecture  1101 . 
         [0073]    Embedding test architecture  1101  within test architecture  1301  requires that the Link and Enable-4, A, B signals  1306  of test architecture  1101  be brought out of test architecture  1301  so they can be controlled by the N-bit LIR via bus  1303 . Thus the N-bit LIR not only provides the Link  606  and Enable  607  signals for test architecture  1301 , but also the Link  606  and Enable signals  1306  for the embedded test architecture  1101 . 
         [0074]      FIG. 14  illustrates in  1410  the N-bit LIR  1302  controlled arrangements  1401 - 1407  of test architecture  1301 . As can be seen in  1410 , the N-bit LIR can be loaded with codes to select; (1) wrapper  307  between SI  1304  and SO  1305  (arrangement  1401 ), (2) wrappers  307  and  308  between SI and SO (arrangement  1402 ), (3) wrapper  307  and test architecture  1101  between SI and SO (arrangement  1403 ), (4) wrappers  307 ,  308 , and test architecture  1101  between SI and SO (arrangement  1404 ), (5) wrapper  308  between SI and SO (arrangement  1405 ), (6) wrapper  308  and test architecture  1101  between SI and SO (arrangement  1406 ), and (7) test architecture  1101  between SI and SO (arrangement  1407 ). 
         [0075]      FIG. 14  further illustrates in  1420  that when test architecture  1101  is included in a test architecture  1301  arrangement between SI  1304  and SO  1305 , the N-bit LIR provides control for selecting the particular arrangement between the  1101  test architectures SI  1102  and SO  1103 . As can be seen in  1420 , the N-bit LIR can be loaded with codes to select; (1) wrapper  1002  between SI  1102  and SO  1103  (arrangement  1201 ), (2) wrappers  1002  and  1004  between SI and SO (arrangement  1202 ), (3) wrapper  1002  and  1006  between SI and SO (arrangement  1203 ), (4) wrappers  1002 ,  1004 , and  1006  between SI and SO (arrangement  1204 ), (5) wrapper  1004  between SI and SO (arrangement  1205 ), (6) wrapper  1004  and  1006  between SI and SO (arrangement  1206 ), and (7) wrapper  1006  between SI and SO (arrangement  1207 ). 
         [0076]      FIGS. 10-14  have illustrated how one test architecture  1101  of the present Disclosure may be embedded within another test architecture  1301  of the present Disclosure and both test architectures accessed using a single LIR. For simplification, only one test architecture  1101  was illustrated as being embedded in test architecture  1301 . However, it should be understood that a plurality of test architectures  1101  can be embedded in test architecture  1301 . For example, substituting a second test architecture  1101  for wrapper  308  and a third test architecture  1101  for wrapper  307  in  FIG. 13  would illustrate the embedding of three  1101  test architectures within test architecture  1301 . 
         [0077]    While only a single level of test architecture embedding was shown, i.e. test architecture  1101  embedded within test architecture  1301 , it is clear that the multiple levels of test architecture embedding is possible using the present Disclosure. When multiple levels of test architecture embedding is performed, the number of control signals that must be output from the LIR increases, as can be understood from the inspection of bus  1303  of  FIG. 13 . At some point the number of LIR output control signals may reach a level that is unacceptable due to wire routing concerns within an IC. The following describes an alternate embodiment of the present Disclosure that provides a solution to this LIR output control signal wire routing problem. 
         [0078]      FIG. 15  illustrates an alternate preferred test architecture  1501  according to the present Disclosure that combines the core  4  test architecture  1101  of  FIG. 11  with a LIR  1502 . LIR  1502  is similar to LIR  801  of  FIG. 8A  with the exception that gating circuitry  1503  replaces gating circuitry  807 . Gating circuitry  1503  provides, in addition to the select signal from control bus  109 , an additional input for a test architecture enable (TAENA) signal  1504 . The TAENA signal  1504  is similar to the select signal  808  in that it operates to; (1) enable gating circuitry  1503  to pass control bus signals  109  to the 3-bit IR during instruction scan operations, or (2) disable gating circuitry  1503  from passing control bus signals  109  to the 3-bit IR during instruction scan operations. Thus the only time the 3-bit IR receives control bus  109  signals is when TAENA  1504  and select  808  are both set to enable gating circuitry  1503  to pass control bus  109  signals to the 3-bit IR. 
         [0079]      FIG. 16  illustrates a test architecture  1601  of the present Disclosure which contains wrapper  307 , wrapper  308 , and the test architecture  1501  of  FIG. 15 . Test architecture  1601  is similar to the test architecture  1301  of  FIG. 13  with the exception that test architecture  1501  has been substituted for test architecture  1101 . Test architecture  1601  is serially connected to an N-bit LIR  1602  which provides control input via bus  1603  to the Link  606  and Enable  607  buses of test architecture  1601  and the TAENA signal  1504  to test architecture  1501 . The N-bit LIR  1602  is similar to the N-bit LIR  1302  except that it contains a reduced number of bits and control signal outputs, since it does not need to decode all the Link and Enable-4, A, B signals that were required by the embedded test architecture  1101  of test architecture  1301 . Embedding test architecture  1501  within test architecture  1601  only requires that the TAENA signal  1504  be brought out of test architecture  1601  so it can be controlled by the N-bit LIR via bus  1603 . 
         [0080]      FIG. 17  illustrates in  1710  the N-bit LIR  1602  controlled arrangements  1701 - 1707  of test architecture  1601 . As can be seen in  1710 , the N-bit LIR can be loaded with codes to select; (1) wrapper  307  between SI  1612  and SO  1613  (arrangement  1701 ), (2) wrappers  307  and  308  between SI and SO (arrangement  1702 ), (3) wrapper  307  and test architecture  1501  between SI and SO (arrangement  1703 ), (4) wrappers  307 ,  308 , and test architecture  1501  between SI and SO (arrangement  1704 ), (5) wrapper  308  between SI and SO (arrangement  1705 ), (6) wrapper  308  and test architecture  1501  between SI and SO (arrangement  1706 ), and (7) test architecture  1501  between SI and SO (arrangement  1707 ). 
         [0081]      FIG. 17  further illustrates in  1720  that when test architecture  1501  is included in a test architecture  1601  arrangement between SI  1612  and SO  1613  by appropriate setting of the TAENA signal  1504 , the 3-bit LIR  1502  of test architecture  1501  is included in the arrangement and made accessible during instruction scan operations. The 3-bit LIR of test architecture  1501  can be scanned to select any particular arrangement between the 1501 test architectures SI  1505  and SO  1506 . As can be seen in  1720 , the 3-bit LIR  1502  can be loaded with codes to select; (1) wrapper  1002  between SI  1505  and SO  1506  (arrangement  1501 ), (2) wrappers  1002  and  1004  between SI and SO (arrangement  1502 ), (3) wrapper  1002  and  1006  between SI and SO (arrangement  1503 ), (4) wrappers  1002 ,  1004 , and  1006  between SI and SO (arrangement  1504 ), (5) wrapper  1004  between SI and SO (arrangement  1505 ), (6) wrappers  1004  and  1006  between SI and SO (arrangement  1506 ), and (7) wrapper  1006  between SI and SO (arrangement  1507 ). 
         [0082]    It should be clear from  FIG. 17  that when test architecture  1501  is included in an arrangement  1710  of test architecture  1601 , two LIRs will be scanned in series during instructions scan operations, LIR  1602  and LIR  1502 . Also it should be clear that since LIR  1502  provides within the test architecture  1501  all the control signals required to select the test architecture  1501  arrangements  1720 , via bus  804  of  FIG. 15 , the wire routing problem mentioned in regard to  FIG. 13  is significantly reduced. The only control signal LIR  1602  needs to provide to include test architecture  1501  in an arrangement  1710  is the TAENA signal  1504 . Once included, the LIR  1502  of test architecture  1501  becomes enabled and can be scanned to provide all the additional signals required for selecting arrangements  1720  within test architecture  1501 . 
         [0083]    The advantage test architecture  1501  has over test architecture  1101  is that when test architectures  1501  is embedded within another test architecture  1601 , only the TAENA  1504  signal of test architecture  1501  is required to be brought out of the other test architecture  1601  to be accessed by a LIR  1602  connected to the other test architecture  1601 . This can be compared to test architecture  1301  of  FIG. 13  where it was required to bring out the Link &amp; Enable-4, A, B signals of test architecture  1101  to be connected to LIR  1302 . As described earlier in regard to test architecture  1101  and  1301  of  FIG. 13 , multiple test architectures  1501  could have been shown embedded within test architecture  1610 , by simply substituting a second and third test architecture  1501  for wrappers  308  and  307  respectively. 
         [0084]    The process of making the TAENA signal of an embedded test architecture, like  1501 , externally available at the I/O boundary of a next higher level test architecture, like  1601 , forms the basis of a framework that can be used to access any hierarchically positioned test architecture within an IC. The following provides an example of this hierarchical test architecture access framework and the process for selecting embedded test architectures contained therein. 
         [0085]      FIG. 18  illustrates a test architecture  1801  containing wrapper  307 , wrapper  308 , and the test architecture  1610  of  FIG. 16 . Test architecture  1610  is similar to test architecture  1501  in that it combines a LIR  1602  with test architecture  1601 , as test architecture  1501  combined the LIR  1502  with test architecture  1101 . Test architecture  1610  has a TAENA signal  1611 , as test architecture  1501  has a TAENA signal  1504 . Test architecture  1610  is associated with a core  5 , as test architecture  1501  is associated with a core  4 . The LIR  1802  is connected to the TAENA  1611  signal of test architecture  1601  via bus  1803 , as LIR  1602  is connected to TAENA  1504  signal of test architecture  1601  via bus  1603 . 
         [0086]    The process steps of accessing test architecture  1101  embedded within test architecture  1501 , which is further embedded within test architecture  1610 , which is still further embedded within test architecture  1810 , is as follows. The process steps below are assumed to start at a point where only wrapper  307  and LIR  1802  of  FIG. 18  are in the serial path between SI  1812  and SO  1813  of  FIG. 18 , similar to arrangement  9001  shown in  FIG. 9 . 
         [0087]    Step 1 Perform a first instruction scan operation to load LIR  1802  with a code that sets TAENA  1611 , via bus  1803 , to a state that enables test architecture  1610 . Following this instruction scan operation, test architecture  1610  and LIR  1802  are in the serial path between SI  1812  and SO  1813 . 
         [0088]    Step 2 Perform a second instruction scan operation to load LIR  1802  with a code that maintains TAENA  1611  at a state enabling test architecture  1610 , and to load LIR  1602  of test architecture  1610  with a code that sets TAENA  1504  to a state that enables test architecture  1501 . Following this instruction scan operation, test architecture  1501 , LIR  1602 , and LIR  1802  are in the serial path between SI  1812  and SO  1813 . 
         [0089]    Step 3 Perform a third instruction scan operation to load LIR  1802  and LIR  1602  with codes that maintain TAENA  1611  and TAENA  1504  at states enabling test architectures  1610  and  1501 , and to load LIR  1502  of test architecture  1501  with a code that selects a desired arrangement  1201 - 1207  of test architecture  1101 . Following this instruction scan operation, the selected arrangement  1201 - 1207  of test architecture  1101 , LIR  1502 , LIR  1602 , and LIR  1802  are in the serial path between SI  1812  and SO  1813 . 
         [0090]    Step 4 Perform subsequent instruction and/or data scan operations to the selected arrangement  1201 - 1207  of test architecture  1101  as required to perform a desired test or other operation via the SI  1812  and SO  1813  terminals of the test architecture  1810  of  FIG. 18 . During subsequent instruction scan operations, the codes loaded into LIRs  1502 ,  1602 , and  1802  should maintain access to the currently selected arrangement of test architecture  1101 , unless a new arrangement is needed. Since, as previously mentioned in regard to  FIG. 8A , data scan operations cannot change existing LIR codes, the access to test architecture  1101 , setup by Steps 1-3 above, is not effected during subsequent data scan operations. 
         [0091]    At some point in accessing embedded test architectures using data scan operations, the accumulation of the LIR bypass paths, i.e. the direct connection path coupling the LIR input  802  to the LIR output  803  via multiplexer  806  of  FIG. 8A , may become to long for data to propagate at a desired data scan clock rate. In some cases therefore, it may be necessary to add a resynchronization flip-flop in the serial path between test architectures, such that during data scan operations the data may be re-timed as it passes between serially connected test architectures. A logical point to insert such a resynchronization flip-flop would be in the LIR bypass path described above. Placing it elsewhere would force instruction scan operations to unnecessarily have to pass through the resynchronization flip-flop. 
         [0092]      FIG. 19  illustrates an LIR  1901  containing a resynchronization register/flip-flop  1904  in the bypass path of the LIR. LIR  1901  is simply LIR  801  adapted to include flip-flop  1904  in the bypass path between LIR input  802  and LIR output  803  and circuitry  1902  and  1903  to enable the flip flop  1904  to receive control bus  109  input during data scan operations. During data scan operations the select signal will be low to select the registered bypass path through multiplexer  806  to SO  803 . Inverter  1902  inverts the select signal so that during data scan operations And gating circuit  1903  passes bus  109  to flip flop  1904 . In response to the clock signal of bus  109 , flip-flop  1904  moves data from SI  802  to SO  803 . Use of LIR  1901  with a registered bypass path between input  802  and output  803  eliminates the above-described concern of using LIRs with direct connection bypass paths between input  802  and output  803 . 
         [0093]      FIG. 20  illustrates a serial configuration  2001  of test architectures  2006 - 2008 . The test architectures  2006 - 2008  are connected in a serial path between SI  2004  and SO  2005 . The serial path includes a LIR  2002  that provides the link and enable control bus  2003  to the test architectures. Each test architecture and the LIR receive control input from control bus  109 . A TAENA  2009  signal is shown being input to the LIR  2002  to indicate that the serial configuration  2001  of test architectures  2007 - 2008  may itself be a test architecture according to the present Disclosure, being enabled and disabled by TAENA  2009  as previously described in regard to  FIGS. 15 ,  16 , and  18 . If serial configuration  2001  is viewed as a test architecture  2001 , it could be embedded within another test architecture as test architectures  1501  and  1610  were embedded within other test architectures  1610  and  1810 , respectively. The following description assumes the serial configuration (or test architecture)  2001  is enabled by TAENA  2009 . 
         [0094]    During instruction or data scan operations data flows through the selected arrangement of each test architecture  2006 - 2008  and through the LIR from SI  2004  to SO  2005 . If testing or other operation, such as emulation, is to be performed on only one of the test architectures, say on test architecture  2007 , the selected arrangements of other test architectures  2006  and  2008  must be serially traversed during the application of the test or other operation. The following description illustrates a modification to the test architectures  2006 - 2008  that prevents having to traverse arrangements within test architectures that are not involved in a test or other operation. This modification will be described as it would be applied if test architectures  2006 - 2008  are of the type  601  shown in  FIG. 6A . To illustrate that test architectures  2006 - 2008  are of type  601 , the SIs and SOs of test architectures  2006 - 2008  are each labeled as SI  604  and SO  605 . 
         [0095]    In  FIG. 21 , a group of arrangements  2101 - 2108  for the modified test architectures  601  are shown. In comparing the group of arrangements of  FIG. 21  to that of  FIG. 7 , it is seen that arrangements  2101 - 2107  of  FIG. 21  are identical to the arrangements  7001 - 7007  of  FIG. 7 . The difference between the  FIGS. 7 and 21  arrangements is that a new wrapper bypass arrangement  2108  has been added in the arrangements of  FIG. 21 . This new wrapper bypass arrangement  2108  provides for directly connecting the SI  604  input and SO  605  output of modified test architectures  601 , such that all wrappers  307 - 309  contained within the modified test architectures  601  may be disabled and disconnected (bypassed) from the serial path between SO  604  and SO  605 . 
         [0096]      FIG. 22  illustrates how the output linking circuitry  603  of  FIG. 6C  is modified to allow for the new wrapper bypass arrangement  2108 . The modification involves replacing the three input multiplexer  611  of  FIG. 6C  with the four input multiplexer  2201  of  FIG. 22  and connecting the SI  604  input of test architecture  601  to the fourth input of multiplexer  2201 . In addition to this modification of the output linking circuitry  603 , bypass codes for each of the test architectures  2006 - 2008  need to be added to the LIR  2002  to enable selecting the wrapper bypass arrangement  2108  of  FIG. 21  in each of the test architectures  2006 - 2008 . The following description of a bypass code for test architecture  2006  is given. 
         [0097]    When the LIR  2002  contains a bypass code for test architecture  2006 , it will output control on bus  2003  to input SELSO  2202  control to multiplexer  2201  to form the wrapper bypass arrangement  2108  between the SI  604  input and SO  605  output of test architecture  2006 . Also when LIR  2002  contains the bypass code it will disable the wrappers  307 - 309  of test architecture  2006  from responding to control bus  109  by setting their Enable-1, 2, 3 inputs low via bus  2003 . While test architecture  2006  is controlled to the wrapper bypass arrangement  2108 , data passes directly from its SI  604  input to SO  605  output during instruction and data scan operations occurring in the serial test architecture configuration  2001  of  FIG. 20 . 
         [0098]    If test architectures  2006  and  2008  are controlled to the above described wrapper bypass arrangement  2108  of  FIG. 21  while test architecture  2007  is controlled to say the 2105 arrangement of  FIG. 21 , i.e. core  2  wrapper  308  is selected, then testing or other operations can occur on the wrapper of core  2  in test architecture  2007  without having to traverse wrapper arrangements in the leading  2006  and trailing  2008  test architectures of  FIG. 20 . Thus more efficient serial access is provided to the wrapper of core  2  of test architecture  2007  using the wrapper bypass arrangements  2108  in test architectures  2006  and  2008 . This increase in serial access efficiency would be even more pronounced if the example of  FIG. 20  had shown a multiplicity of serially connected test architectures preceding and following the target test architecture  2007 . 
         [0099]    While the modification to include a wrapper bypass arrangement  2108  has been described as it would apply to the type  601  test architecture of  FIG. 6A , it is a general modification that can be applied to any of the test architectures described herein. For example, test architecture  1301  of  FIG. 13 , test architecture  1501  of  FIG. 15 , test architecture  1610  of  FIG. 16 , and test architecture  1810  of  FIG. 18  could all be modified to include the wrapper bypass arrangement described above. 
         [0100]    In test architectures that contain an embedded LIR, i.e. test architectures  1501 ,  1610 , and  1810 , the embedded LIR would include the above described wrapper bypass codes required to select the wrapper bypass arrangement  2108  of the test architecture. Including the wrapper bypass arrangement in all the above-mentioned test architectures would serve to improve the serial access efficiency when the test architectures are placed into a serial configuration  2001  as shown in  FIG. 20 . 
         [0101]    In test architectures that contain an embedded LIR (i.e.  1501 ,  1610 ,  1810 ), it is preferable to use the LIR  1901  of  FIG. 19  as opposed to LIR  801  of  FIG. 8A , since LIR  1901  allows registering the data transfers during data scan operations. By registering data scan operation transfers, any number of serially connected test architectures may be placed in the wrapper bypass arrangement  2108  and operated without having to reduce the data scan clock frequency, as described in regard to  FIG. 19 . In test architectures that do not contain an embedded LIR (i.e.  601 ), it may be necessary to insert a data resynchronization circuit (DRC) at points along the serial path connecting multiple test architectures to maintain a desired scan clock rate through the serial path when multiple test architectures are placed in the wrapper bypass arrangement  2108 . 
         [0102]    For example,  FIG. 23  illustrates the serial connection  2301  of the multiple test architectures  2006 - 2008  of  FIG. 20  being connected together serially through DRC&#39;s  2302 - 2304 . TAENA  2313  is shown simply to indicate that serial configuration  2301 , like serial configuration  2001 , may be viewed as an embedded test architecture. As seen in  FIG. 23 , DRC  2302  exists between SO  605  of test architecture  2006  and the SI  604  of test architecture  2007 , DRC  2303  exists between SO  605  of test architecture  2007  and SI  604  of test architecture  2008 , and DRC  2304  exists between SO  605  of test architecture  2008  and the SI  802  of LIR  2305 . The DRCs  2302 - 2304  are connected to the clock  2306  signal of control bus  109 , to allow them to operate during both instruction and data scan operations. The DRCs  2302 - 2304  are also connected to bypass select signals  2307 - 2309 , respectively, from LIR output control bus  2312 . The bypass select signals are signals added to the LIR output control bus  2312  when DRCs are used. There is one unique bypass select signal  2307 - 2308  for each DRC  2302 - 2304  to allow separate control of each DRC. 
         [0103]      FIG. 24  illustrates an example DRC circuit. The DRC contains a flip-flop (FF)  2403  and a multiplexer  2402 . The DRC has a SI  2404  that is input to the multiplexer and FF. The output of the FF is input to the multiplexer. The multiplexer has a control input  2407  and a SO  2405 . The FF has a clock input  2406 . The control inputs  2407  of DRC  2302 - 2304  of  FIG. 24  are connected to the bypass select signals  2307 - 2309  respectively. The clock inputs  2406  of DRCs  2302 - 2304  of  FIG. 24  are connected to control bus  109  clock signal  2306 . The SIs  2404  of DRCs  2302 - 2304  of  FIG. 24  are connected to the SOs  605  of test architectures  2006 - 2007  respectively. The SOs  2405  of DRCs  2302 - 2304  of  FIG. 24  are connected to the SI  604  of test architecture  2007 , the SI  604  of test architecture  2008 , and SI  802  of LIR  2305  respectively. 
         [0104]    If LIR  2305  is loaded with a bypass code for test architecture  2006 , the bypass select signal  2307  will be set cause DRC  2302  to place FF  2406  between the SO output of test architecture  2006  and SI input of test architecture  2007 . For all other codes, bypass select will be set to cause DRC  2302  to directly connect the SO output of test architecture  2006  to the SI input of test architecture  2007  via multiplexer  2402 . 
         [0105]    If LIR  2305  is loaded with a bypass code for test architecture  2007 , the bypass select signal  2308  will be set cause DRC  2303  to place a FF  2406  between the SO output of test architecture  2007  and SI input of test architecture  2008 . For all other codes, bypass select will be set to cause DRC  2303  to directly connect the SO output of test architecture  2007  to the SI input of test architecture  2008  via multiplexer  2402 . 
         [0106]    If LIR  2305  is loaded with a bypass code for test architecture  2008 , the bypass select signal  2309  will be set cause DRC  2304  to place a FF  2406  between the SO output of test architecture  2008  and SI input of LIR  2305 . For all other codes, bypass select will be set to cause DRC  2304  to directly connect the SO output of test architecture  2008  to the SI input of LIR  2305  via multiplexer  2402 . 
         [0107]    As can be seen from the above description of  FIGS. 23 and 24 , when a test architecture is placed in the wrapper bypass arrangement, the DRC associated with the SO output of the test architecture is set to insert FF  2406  between its SI  2404  and SO  2405 . During instruction and data scan operations, this inserted FF  2406  registers the data output from the test architecture in the wrapper bypass arrangement to the SI input of the next serially connected test architecture. 
         [0108]    Also as can be seen from the above description of  FIGS. 23 and 24 , when a test architecture is not placed in the wrapper bypass arrangement, the DRC associated with the SO output of the test architecture is set to form a direct path between its SI  2404  and SO  2405 . During instruction and data scan operations, this direct path simply passes the data from the SO output of the leading test architecture to the SI input of the trailing test architecture. Directly connecting the SO output of a test architecture not in the wrapper bypass arrangement is fine since all other selectable arrangement will include registration in the form of one of the data registers  106 - 108  described in regard to  FIG. 1 . 
         [0109]    While insertion of DRC FFs  2406  and/or LIR FFs  1904  in the serial path of series connected test architectures, such as  FIG. 23 , takes away from the test pattern reuse advantage  3  stated earlier in regard to  FIGS. 8 and 9 , it offers the advantage of being able to operate serially connected test architectures at high clock frequencies. Thus while test patterns may need to be modified when FF  2406 / 1904  bit positions are inserted in the path between serially connected test architectures, the inserted bit positions facilitate high speed clocking of the data through serially connected test architectures. 
         [0110]    While DRCs in  FIGS. 23 and 24  have been described as they would be used to register or pass serial test/emulation data between test architecture circuits  2007 - 2008 , it should be understood that the DRCs could also be used to register or pass functional data between functional circuits as well. For example, circuits  2006 - 2007  could represent functional circuits in an IC or on a board, such as microprocessors, digital signal processors, memories, mixed signal circuits (A/D, D/A), or any other type of circuits that are connectable via their inputs and outputs to communicate data. Using DRCs, the data communicated between functional circuits could selectively be communicated in either a registered or non-registered form, as described above in regard to  FIGS. 23 and 24 . 
         [0111]    Although the present Disclosure has been described in accordance to the embodiments shown in the figures, one of ordinary skill in the art will recognize there could be variations to these embodiments and those variations should be within the spirit and scope of the present Disclosure. Accordingly, modifications may be made by one ordinarily skilled in the art without departing from the spirit and scope of the appended claims.