Abstract:
The present invention provides a microelectronic device with a circuit core and a boundary scan test interface sharing a number of pre-selected pins. In the mode of a boundary scan test, the boundary scan test interface manipulates the input and output of the test signal through the shared pins. Pins necessary for the microelectronic device are therefore reduced.

Description:
BACKGROUND 
       [0001]    1. Field of The Invention 
         [0002]    The present invention relates to a microelectronic device, and in particular, to a microelectronic device provided with an integrated circuit core and a boundary scan test interface, which share a number of pre-selected pins. 
         [0003]    2. Description of Related Art 
         [0004]    In a printed circuit board(PCB) on which a plurality of microelectronic devices such as integrated circuits(ICs) are mounted, an interconnection test is required to assure correct interconnections between respective ICs on the board. For example, the Boundary Scan test which is compliant with IEEE 1149.1 standard A is a typical measure for such an interconnection test. 
         [0005]    In general, the microelectronic device includes an IC core for execution of main functions, and a boundary scan test interface for testing.  FIG. 1  illustrates an example of a conventional microelectronic device  101 , which comprises an IC core  101 , a boundary scan test interface architecture for boundary scan tests, and pins dedicated to the architecture. As shown in  FIG. 1 , the boundary scan test interface includes a test access port(TAP) controller  102 , an instruction register  103 , a bypass register  10 , and boundary scan units  105 . In  FIG. 1 , there are five pins dedicated to the boundary scan test, which are pin TDI, pin TDO, pin TCK, pin TMS, and pin TRST, respectively. In other function modes of the microelectronic device  100 , these pins are not to be used. When the boundary scan test mode is performed, the pin TDI is used for inputting serial data, the pin TDO is used for outputting serial data, the pin TMS is used for selecting input, the pin TCK is used for clock input, and the pin TRST is used for resetting the system. Among these pins, the pin TRST is not essential and may be used or removed depending on the design. 
         [0006]    Generally, the TAP controller  102  enters the scan test mode based a signal input from the pin TMS. For example, when the signal input to the pin TMS is 0(low level), the TAP controller  102  enters the boundary scan test mode. In the boundary scan test mode, the TAP controller  102  controls serial test data to be input from the pin TDI and output to another electronic device via a scan chain formed with a plurality of boundary scan units  105 , in order to test whether the interconnection between the microelectronic device  100  and the electronic device is normal. After completing such tests, if the microelectronic device operates in the normal operation mode, the boundary scan test interface does not have to be functional any more and these dedicated pins are then idle. In other words, these pins are redundant in the operation modes other than the boundary scan test mode. 
         [0007]    As to functions of the instruction register  103 , the bypass register  104 , and the boundary scan units  105  in the boundary scan test mode, please refer to the IEEE 1149.1 standard. Detailed explanations are omitted here for the sake of brevity. 
         [0008]    The number of pins consumed affects the fabrication cost of IC chips. In other words, the greater the number is, the higher the cost is. Therefore, if the number of pins necessary for an IC chip can be reduced, the fabrication cost can be reduced significantly. 
       SUMMARY 
       [0009]    In view of the above, the present invention provides a microelectronic device having pins shared by the boundary scan test mode and other modes. 
         [0010]    In addition, another object of the present invention is to provide a pin arrangement method capable of reducing the cost. 
         [0011]    According to one aspect, the present invention provides a microelectronic device comprising (a) an IC core, and (b) a boundary scan test interface sharing with the IC core a pre-selected number of pins, each of which can be switched between the scan test mode and a normal function operation mode. In one preferred embodiment, the interface includes (b1) one mode selection input pin, and(b2) a test access port controller, which activates the boundary scan test mode to route the test signal so as to be input or output through the pre-selected shared pins, based on an mode selection signal input from the mode selection input pin. 
         [0012]    According to the present invention, the boundary scan test interface further includes a test signal route selector to decide whether the pre-selected shared pins are in the boundary scan test mode or the normal function operation mode, or/and whether the pre-selected shared pins are input pins or output pins. The test signal route selector makes the decision based on a state of the test access port controller, or a result of a logical operation of the state of the test access port controller with the mode selection signal. 
         [0013]    The number of the shared pins may be 1, 2, 3, or 4. In the test mode, the shared pins may function as data input pins, data output pins, clock input pins, or system reset input pins. 
         [0014]    Further, the present invention provides a pin arrangement method of a microelectronic device comprising the steps of: providing the microelectronic device having pins for a boundary scan test mode and a normal function operation mode; arranging one of the pins to function as a data input pin, a data output pin, a clock input pin, or a system reset input pin in the boundary scan test mode; and arranging the pin to function as a normal function pin. 
         [0015]    In the accompanying drawings and the following descriptions, details of one or more embodiments of the present invention will be illustrated. The abovementioned and other objects, features, and advantages of the present invention will be more readily apparent from the following description, drawing, and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In the accompanying drawings, 
           [0017]      FIG. 1  shows a conventional microelectronic device having boundary scan test interface; 
           [0018]      FIG. 2  shows a microelectronic device having boundary scan test interface according to one embodiment of the present invention; 
           [0019]      FIG. 3  shows a state diagram of a state machine of a test access port(TAP) controller; and 
           [0020]      FIG. 4  shows a microelectronic device having boundary scan test interface according to another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    In the detailed descriptions below, various details will be disclosed to be contributory to the complete understanding of the present invention. However, those having ordinary knowledge of this field can implement the present invention without using specific details disclosed below. Therefore, any alternatives, modifications, or changes of the embodiments illustrated should be considered to be within the scope of the present invention. 
         [0022]    First, please refer to  FIGS. 2 and 3 .  FIG. 2  shows a microelectronic device  200  according to one embodiment of the present invention.  FIG. 3  is a state diagram for illustrating a state of a state machine of a test access port controller (abbreviated to TAP hereinafter) shown in  FIG. 2 . 
         [0023]    As shown in  FIG. 2 , the microelectronic device  200  comprises an integrated circuits (IC) core  201  for executing normal operation functions, a tap controller  202 , an instruction register  203 , a bypass register  204 , a boundary scan unit  205 , an OR gate  206 , and multiplexers  210 ,  211 , and  214 . 
         [0024]    In  FIG. 2 , some pins are denoted by the abbreviations of TDI, TDO, TCK, and TRST for the convenience of explanation. However, these pins in contrast to the conventional pins are portrayed differently according to embodiments of the present invention. Instead of using the conventional pins for only the boundary scan test mode, these pins can be shared by the boundary scan mode and the normal function operation mode of the IC core  201 . In the normal function operation mode, they may function as one-way input pins, one-way output pins, or bi-direction(input/output) pins in order to work in cooperation with the normal function operation mode of IC core  201 . In this embodiment, an example is given that a bi-direction pin is used to function as the TDI and TDO pin in the boundary scan test mode. However, it should be noted that the one-way input pin and the one-way output pin may also be selected as the TDI pin and the TDO pin in the boundary scan test mode, respectively. It should be noted that depending on the requirements of a certain IC, one could select a one-way pin or a bi-direction pin to function as a desired switchable pin. 
         [0025]    Please refer to  FIG. 3 .  FIG. 3  shows a switch operation between the boundary scan test mode (also called as the JTAG mode) and the normal operation mode of the microelectronic device  200 . As discussed previously, the interconnection test is performed on the microelectronic device and other IC or electronic device in the boundary scan test mode, while the IC core performs its function operation in the operation modes other than the boundary test mode. 
         [0026]    As shown in  FIG. 3 , when an external signal input from the TMS pin is 0, the state machine exits from the Test_Logic_Reset state, and enters into the Run_Test/Idle state, i.e. the boundary scan test mode. Upon starting, the microelectronic device  200  outputs a signal from an analog front end device (AFE)  230  shown in  FIG. 2 , in order to activate the TAP controller  202  to enter into the Test_Logic_Reset state. 
         [0027]    The state signal TAP_CTRL indicates the state of the TAP controller  202 . The state signal TAP_CTRL is 1 (high level) when the microelectronic device  200  is in the normal function operation mode, and the state signal TAP_CTRL is 0 (low level) when it enters the boundary scan test mode. In  FIG. 2 ,  1 ′b 1  (high level)indicates that this state signal is in Test_Logic_Reset, and  1 ′b 0  (low level)indicates that this state signal is in the boundary scan test mode. At this time, since the logic gate  206  receives the state signal TAP_CTRL as one input and receives the TMS signal as the other input, its output signal BS_MODE is 1 (high level). The logic gate  206  may be an OR gate receiving an inverted signal, or an equivalent NAND gate. When the signal BS_MODE is 1, the multiplexers  210  and  212  will select  1 ′b 0  and  1 ′b 1  as their outputs OE 1  and OE 2 , respectively, and accordingly the output OE 1  is low level and the output OE 2  is high level. 
         [0028]    As shown in  FIG. 2 , a bi-direction circuit  220  connected to the pin TDI is controlled by the output OE 1 (=0) to make the pin TDI to function as an signal input pin, while a bi-direction circuit  222  connected to the pin TDO is selected by the output OE 2 (=1) so as to make the pin TDO function as the signal output pin. The multiplexer  214  is activated by the signal BS_MODE to select a signal output from the multiplexer  216 (i.e. the signal input from the pin TDI) as its output signal. 
         [0029]    If the state of the TAP controller is the Test_Logic_Reset state, then the output signal BS_MODE of the logic gate  206  is 0, and accordingly the multiplexers  210  and  212  are not activated. In this situation, the selected pins TDI and TDO may be used in the other modes. In brief, all of the shared pins are in the boundary scan test mode when the output signal BS_MODE is 1, and in the normal function operation mode when the output signal BS_MODE is 0. 
         [0030]    The other states of the state machine shown in  FIG. 3  are used as examples only for explaining the operation of the boundary scan test. Therefore, the figure is provided to those skilled in this field for reference and details of the boundary scan test are not discussed herein. 
         [0031]    In the above descriptions about this embodiment, although the bi-direction pins are used as the shared pins TDI and TDO, various combinations of the pins suitable for the shared pin TDI and TDO are still within the scope of the present invention. For example, the one-way input pin and the one-way output pin, the one-way input pin and the bi-direction output pins, or the bi-direction pin and the one-way output pin may be used as the shared pins TDI and TDO, respectively. 
         [0032]    The pins TCK and TRST shown in  FIG. 2  may also be selected as the shared pins; nonetheless, the pin TRST may be removed eventually depending on the requirements of the design since it is not necessary at all. For simplicity, the hardware structures for the shared pins TCK and TRST are not shown in the figure since they share similar structures as the circuits for pins TDI and TDO. It should be noted that the design of the logical gate  206  is provided for the situation that the pin TCK is designed as a shared pin. If the pin TCK is designed as an unshared pin, the logical gate  206  does not have to exist. In detail, since the TAP controller  202  operates based on the clock signal TCK, its state is kept in the Test_Logic_Reset at the initial stage of the circuit if the pin TCK is not shared, and accordingly the pin TCK is kept as the normal function pin, and does not provide the test clock signal to the TAP controller  202 . In this situation, the TAP controller  202  will not change its state because it does not receive the test clock signal TCK. Thus, according to this embodiment, the pin TCK is switched from the normal function mode to the boundary scan test mode based on the TMS signal, thereby to change the state of the TAP controller  202 . If the pin TCK is not shared or is switched in other ways so as to make the TAP controller  202  able to receive the test clock signal, then it is not necessary to provide the logic gate  206 . Such cases are apparently still within the scope of the present invention. 
         [0033]      FIG. 4  shows a microelectronic device according to another embodiment of this invention. The microelectronic device  300  shown in  FIG. 4  is different from that shown in  FIG. 3  in that an inverter  306  replaces the OR gate  206  receiving the inverted input. The other parts shown in  FIG. 4  are similar to those in  FIG. 3  and descriptions of such similar structures are not repeated here. The state control signal TAP_CTRL is inverted into the BS_MODE signal by the inverter  306 . However, in this embodiment, the operation modes of pins are not switched based on the TMS signal. In this embodiment, the inverter  306  for replacing the OR gate  206  is give as one example only. If the state signal of the TAP controller  202  indicates a contrary meaning, the inverter  306  can be omitted. 
         [0034]    According to the present invention, the microelectronic device can allow the pin TMS to be used only in the boundary scan test mode, and the other pins TDI, TDO, TCK, and TRST to be shared by the boundary scan test mode and the other function modes, i.e. by the IC core and the boundary scan test interface, depending on the design requirements. Further, since the shared pins may be one-way or bi-direction pins, the present invention can provide a designer with greater design flexibility. Thus, according to the present invention, since many predetermined pins can be shred by the boundary scan test mode and the general function operation mode, the cost of the microelectronic device can be reduced. 
         [0035]    While the present invention has been explained with reference to preferred embodiments, the description is illustrative of the invention only to help those skilled in this art to understand the present invention, and is not to be construed as limiting the invention. Various modifications and variations may be made by those skilled in this art without departing the spirits of the present invention. In view of the foregoing, it is intended that the present invention cover all such modifications and variations, which should be interpreted to fall within the scope defined by the appended claims and their equivalents.