Abstract:
A semiconductor device includes both a logic circuit and a macro circuit. The macro circuit includes a circuit that consumes direct current (DC). In order to conserve power and allow for testing, the consumption of DC by the current consumption circuit can be stopped with a stop signal, which stops the operation of the macro circuit. The macro circuit can be restarted or returned to normal operation mode without risk of error caused by the stopping of the macro circuit.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a semiconductor device, and, more particularly, to a semiconductor device on which a logic circuit and a macro circuit, such as a macro memory that consumes more power than the logic circuit, are both mounted.  
         [0002]      FIG. 1  is a schematic block diagram of a semiconductor device  100  on which a macro memory circuit  1  and a logic circuit  2  are both mounted. A common external power supply voltage is supplied to the memory circuit  1  and the logic circuit  2 .  
         [0003]     The memory circuit  1  comprises a plurality of internal power supply generation circuits which generate a plurality of different internal power supply voltages.  FIG. 2  is a schematic circuit diagram of a substrate potential generation circuit  3  which is one of the plurality of internal power supply generation circuits.  
         [0004]     The substrate potential generation circuit  3  includes a substrate potential detection circuit  4 , an oscillator circuit  5  and a pump circuit  6 . The substrate potential detection circuit  4  includes a P-channel MOS transistor Tr 1  having a source connected to a high potential power supply Vcc via a resistor R 1  and a drain connected to a low potential power supply Vss. A substrate potential VBB is supplied to the gate of the transistor Tr 1  and the source (a node N 1 ) of the transistor Tr 1  is connected to the input terminal of an inverter circuit  7   a . The output signal of the inverter circuit  7   a  is supplied to the oscillator circuit  5  via an inverter circuit  7   b.    
         [0005]     In the substrate potential detection circuit  4 , the drain current of the transistor Tr 1  decreases along with an increase of the substrate potential VBB, and the potential of the node N 1  increases along with a decrease of the drain current. If the potential of the node N 1  is equal to or lower than the threshold of the inverter circuit  7   a , the inverter circuit  7   b  outputs a signal having the L level. When the potential of the node N 1  exceeds the threshold of the inverter circuit  7   a , the inverter circuit  7   b  outputs a signal having the H level.  
         [0006]     The output signal of the substrate potential detection circuit  4  is supplied to a NAND circuit  8   a  and the output signal of the NAND circuit  8   a  is supplied to the pump circuit  6  via an even number of inverter circuits  7   c . The output signal of the inverter circuit  7   c  is also supplied to the NAND circuit  8   a.    
         [0007]     In the oscillator circuit  5 , if the output signal of the substrate potential detection circuit  4  is low, the output signal of the inverter circuit  7   c  is maintained at the H level. When the output signal of the substrate potential detection circuit  4  goes high, the oscillator circuit  5  generates an oscillation signal having a predetermined frequency in accordance with the delay times of the NAND circuit  8   a  and the inverter circuit  7   c.    
         [0008]     The pump circuit  6  includes a capacitor  9  having an input terminal which receives the output signal of the oscillator circuit  5  and an output terminal connected to the anode of a diode  10   a  and the cathode of a diode  10   b . The cathode of the diode  10   a  is connected to the low potential power supply Vss and the substrate potential VBB is input to the anode of the diode  10   b.    
         [0009]     In the pump circuit  6 , the potential of the input terminal of the capacitor  9  rises and falls in accordance with the oscillation signal output from the oscillator circuit  5  and the potential of the output terminal of the capacitor  9  rises and falls due to the capacitive coupling of the capacitor  9 . The substrate potential VBB decreases due to the rising and falling operation.  
         [0010]     In the substrate potential generation circuit  3 , direct current (D.C.) is consumed when a drain current flows in the transistor Tr 1  of the substrate potential detection circuit  4 . Accordingly, the current consumption of the memory circuit  1  comprising a plurality of substrate potential generation circuits  3  is higher than that of the logic circuit  2 . Thus, the normal operation of an internal power supply generation circuit such as the substrate potential generation circuit  3  increases the current consumption of the entire semiconductor device  100 . Further, when the memory circuit  1  operates normally, whether the operating current of the logic circuit  2  is normal cannot be tested.  
         [0011]     To reduce power consumption, the supply of the power to the memory circuit  1  should be cut off when the memory circuit  1  is not used. However, if a power supply voltage is supplied to the memory circuit  1  and the logic circuit  2  via a common power line, the power cannot be cut off only for the memory circuit  1 .  
         [0012]     If a power supply voltage is supplied separately to the memory circuit  1  and the logic circuit  2 , only the power for the memory circuit  1  can be cut off. In this case, however, a malfunction such as hang-up operation or latch-up operation occurs due to the power supply potential difference when the power is cut off, causing the operation to become unstable.  
       SUMMARY OF THE INVENTION  
       [0013]     An object of the present invention is to provide a semiconductor device which operates stably and has reduced power consumption.  
         [0014]     In one aspect of the present invention, a semiconductor device includes a logic circuit and a macro circuit including a circuit that consumes direct current and stops operation in response to a stop signal.  
         [0015]     A first switching circuit may be applied to the direct current consumption circuit. The first switch cuts off the direct current flowing in the direct current consumption circuit in response to the stop signal.  
         [0016]     The macro circuit may include a data transfer circuit for generating a transfer data signal from an input data signal in accordance with a clock signal. A first reset circuit is connected to the data transfer circuit to reset the transfer data signal of the data transfer circuit in response to a reset signal. A power-on reset circuit is connected to the first reset circuit to generate the reset signal when power is provided thereto. A start signal generation circuit generates a start signal when the stop signal is deactivated. A second reset circuit is connected to the start signal generation circuit and the data transfer circuit to reset the transfer data signal in response to the start signal.  
         [0017]     The macro circuit may include a data transfer circuit for generating a transfer data signal from an input data signal in accordance with a clock signal. A power-on reset circuit generates a reset signal when power is provided thereto. A start signal generation circuit generates a start signal when the stop signal is deactivated. A composite circuit is connected to the power-on reset circuit and the start signal generation circuit to generate a composite reset signal by combining the start signal and the reset signal. A reset circuit is connected to the composite circuit to reset the transfer data signal in response to the composite reset signal.  
         [0018]     The macro circuit includes a data transfer circuit for generating a transfer data signal from an input data signal in accordance with a clock signal. A power-on reset circuit generates a reset signal when power is provided thereto. A composite circuit is connected to the power-on reset circuit to generate a composite reset signal by combining the stop signal and the reset signal. A reset circuit is connected to the composite circuit to reset the transfer data signal in response to the composite reset signal.  
         [0019]     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0021]      FIG. 1  is a schematic block diagram of a conventional semiconductor device;  
         [0022]      FIG. 2  is a schematic circuit diagram of a conventional substrate potential generation circuit;  
         [0023]      FIG. 3  is a schematic block diagram of a semiconductor device according to a first embodiment of the present invention;  
         [0024]      FIG. 4  is a schematic block diagram of a semiconductor device according to a second embodiment of the present invention;  
         [0025]      FIG. 5  is a schematic circuit diagram of the substrate potential generation circuit of the semiconductor device of  FIG. 4 ;  
         [0026]      FIG. 6  is a schematic circuit diagram of another example of a substrate potential generation circuit;  
         [0027]      FIG. 7  is a schematic block diagram of a substrate potential generation circuit and a partial cross-sectional view of a substrate;  
         [0028]      FIG. 8  is a schematic block diagram of another substrate potential generation circuit and a partial cross-sectional view of a substrate;  
         [0029]      FIG. 9  is a schematic circuit diagram of a semiconductor device according to a third embodiment of the present invention;  
         [0030]      FIG. 10  is a schematic circuit diagram of a conventional reference voltage generation circuit;  
         [0031]      FIG. 11  is a schematic circuit diagram of a reference voltage generation circuit according to a fourth embodiment of the present invention;  
         [0032]      FIG. 12 ( a ) is a schematic circuit diagram of a start signal generation circuit and  FIG. 12 ( b ) is a signal waveform diagram showing the operation of the start signal generation circuit;  
         [0033]      FIG. 13  is a schematic circuit diagram of a conventional data transfer circuit;  
         [0034]      FIG. 14 ( a ) is a schematic circuit diagram of a power-on reset circuit and  FIG. 14 ( b ) is a signal waveform diagram showing the operation of the power-on reset circuit;  
         [0035]      FIG. 15  is a schematic circuit diagram of a data transfer circuit according to a fifth embodiment of the present invention;  
         [0036]      FIG. 16  is a schematic circuit diagram of a reset circuit according to a sixth embodiment of the present invention; and  
         [0037]      FIG. 17  is a schematic circuit diagram of another example of a reset circuit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     In the drawings, like numerals are used for like elements throughout.  
       First Embodiment  
       [0039]      FIG. 3  is a schematic circuit diagram of a one-chip semiconductor device  200  according to a first embodiment of the present invention. A logic circuit  13  and a macro circuit  12  are mounted on a semiconductor substrate  11  and a common power supply voltage is supplied to both the logic circuit  13  and the macro circuit  12 . The macro circuit  12  receives a stop signal PC via an external terminal  14   a  and enters the stop mode in response to the stop signal PC. In the stop mode, a circuit in the macro circuit  12  which consumes direct current is deactivated, which decreases the current consumption of the macro circuit  12 .  
       Second Embodiment  
       [0040]      FIG. 4  is a schematic circuit diagram of a one-chip semiconductor device  300  according to a second embodiment of the present invention. The semiconductor device  300  comprises the macro memory circuit  12  and the logic circuit  13  each of which is formed on a semiconductor substrate  11 . A plurality of external terminals  14  are formed on the periphery of the semiconductor substrate  11  and a stop signal PC is supplied to the memory circuit  12  from one of the external terminals  14   a . The stop signal PC is used to stop the operation of an internal power supply generation circuit in the memory circuit  12 , which thereby decreases the current consumption of the memory circuit  12 .  
         [0041]     A common power supply voltage is supplied from the common external terminals  14  to the memory circuit  12  and the logic circuit  13 .  
         [0042]     The stop signal PC is supplied to a substrate potential generation circuit  15 , which is the internal power supply generation circuit. As shown in  FIG. 5 , a substrate potential detection circuit  16  of the substrate potential generation circuit  15  includes a P-channel MOS transistor Tr 2  connected between a high potential power supply Vcc and a resistor R 1  and the stop signal PC is supplied to the gate of the transistor Tr 2 . The substrate potential detection circuit  16  serves as an internal power supply potential detection circuit. The substrate potential detection circuit  16  further includes an N-channel MOS transistor Tr 2   a  connected in parallel to a transistor Tr 1  and the stop signal is supplied to the gate of the transistor Tr 2   a.    
         [0043]     In a normal mode in which the memory circuit  12  operates, the stop signal PC has the L level, and in the stop mode in which the memory circuit  12  does not operate, the stop signal has the H level.  
         [0044]     When the stop signal PC has the L level, the transistor Tr 2  is turned on and a drain current flows from the transistor Tr 2  to the transistor Tr 1  via the resistor R 1 . The substrate potential generation circuit  15  is activated and predetermined substrate potential VBB is generated.  
         [0045]     When the stop signal PC has the H level, the transistor Tr 2  is turned off and the transistor Tr 2   a  is turned on. Thereupon, the flow of the drain current (DC current) in the transistor Tr 1  is cut off and the substrate potential generation circuit  15  is deactivated. At this time, an inverter circuit  7   b  outputs a signal having the L level.  
         [0046]     As shown in  FIG. 6 , the stop signal PC is preferably generated by a command decoder  16   a  provided in the memory circuit  12 . The command decoder  16   a  receives a command signal CM from an external device, decodes the command signal CM and generates the stop signal PC. Command decoder circuits are well-known to persons skilled in the art.  
         [0047]     As shown in  FIG. 7 , the stop signal PC is also supplied to the gate of an N-channel MOS transistor Tr 3  via a buffer circuit  17   a . The source of the transistor Tr 3  is connected to a low potential power supply Vss and the drain is connected to a P-type diffusion area  18  on the semiconductor substrate  11 . The P-type diffusion area  18  is formed in an N-type diffusion area  19 .  
         [0048]     The substrate potential VBB, as a low-potential, is supplied to the buffer circuit  17   a . The buffer circuit  17   a  supplies a signal having the substrate potential VBB to the gate of the transistor Tr 3  in response to the stop signal PC having the L level, which turns off the transistor Tr 3 . That is, the buffer circuit  17   a  has a level shift function.  
         [0049]     Next, the operation of the semiconductor device  300  is described.  
         [0050]     The transistor Tr 2  of the substrate potential detection circuit  16  is turned off in response to the stop signal PC having the H level. Thereupon, a node N 1  is set to the L level. The substrate potential detection circuit  16  outputs an output signal having the L level and stops the oscillation operation of the oscillator circuit  5 , i.e., the operation of the substrate potential generation circuit  15 . As a result, the flow of the drain currents of the transistors Tr 2  and Tr 1  of the substrate potential detection circuit  16  are cut off and the switching current of the oscillator circuit  5  is also cut off.  
         [0051]     When the operation of the substrate potential generation circuit  15  stops, the substrate potential VBB becomes unstable. However, even if a noise N invades the P-type diffusion area  18  when the operation of the substrate potential generation circuit  15  stops, a noise current Ib flows to the power supply Vss as the drain current of the transistor Tr 3  because the transistor Tr 3  is turned on. Further, the substrate potential VBB is fixed to the power supply Vss. Therefore, the occurrence of a defect, such as the latch-up operation of the memory circuit  1  or logic circuit  2  due to the noise current is prevented.  
         [0052]     When the buffer circuit  17   a  and the transistor Tr 3  are not provided, as shown in  FIG. 8 , if the operation of the substrate potential generation circuit  15  is stopped using a stop signal PC, the pump circuit  6  enters a state in which a switch is opened. In this state, when the positive potential noise N invades the P-type diffusion area  18  and a voltage exceeding the threshold of the PN junction between the P-type diffusion area  18  and the N-type diffusion area  19  is applied to the PN junction, a high noise current Ia flows in the PN junction.  
         [0053]     The semiconductor device  300  of the second embodiment has the following advantages.  
         [0054]     (1) The substrate potential generation circuit  15  of the memory circuit  12  cuts off the D.C. consumed by the substrate potential generation circuit  15  in accordance with a stop signal PC. Accordingly, the current consumption of the memory circuit  12  is decreased.  
         [0055]     (2) By cutting off the D.C. consumed by the substrate potential generation circuit  15 , test of D.C. when the logic circuit  13  is not being operated and test of an operating current when the logic circuit  13  is being operated can be performed.  
         [0056]     (3) Since the D.C. consumed by the substrate potential generation circuit  15  is cut off without cutting off the power of the memory circuit  12 , the occurrence of a defect such as latch-up operation is prevented.  
         [0057]     (4) The D.C. consumed by the memory circuit  12  is cut off by supplying a stop signal PC from the external terminal  14   a  to the substrate potential generation circuit  15 . Accordingly, the user can optionally select the stop mode in which the current consumption of the memory circuit  12  is decreased and the current test of the logic circuit  13  is enabled.  
         [0058]     (5) If the operation of the substrate potential generation circuit  15  is stopped, the substrate potential VBB is fixed to the power supply Vss level. Accordingly, the occurrence of malfunctions of the memory circuit  12  and the logic circuit  13  due to the noise N is prevented.  
       Third Embodiment  
       [0059]      FIG. 9  is a schematic circuit diagram of a semiconductor device  400  according to a third embodiment of the present invention. The macro memory circuit  12  comprises the substrate potential generation circuit  15 , a boosting power supply generation circuit  21  that generates a boosting power supply Vpp, a deboosting power supply generation circuit  22  that generates a deboosting power supply (step-down power Supply) VII, and a precharge power supply generation circuit  23  that generates a precharge power supply VCP. Each of the boosting power supply generation circuit  21 , the deboosting power supply generation circuit  22 , and the precharge power supply generation circuit  23  has the same configuration as the substrate potential generation circuit  15 , stops the operation in accordance with a stop signal PC, and fixes the stop potential to the potential of the power supply Vcc or Vss.  
         [0060]     The boosting power supply generation circuit  21  generates a power supply voltage of 5 V from the power supply Vcc of 3 V, for example. The deboosting power supply generation circuit  22  generates a power supply voltage of 2 V from the power supply Vcc of 3 V, for example. The precharge power supply generation circuit  23  generates a power supply voltage of 1.5 V from the power supply Vcc of 3 V, for example.  
         [0061]     The stop signal PC supplied to the external terminal  14   a  is supplied to the boosting power supply generation circuit  21 , the deboosting power supply generation circuit  22 , the precharge power supply generation circuit  23  and the substrate potential generation circuit  15  via a buffer circuit  17   b.    
         [0062]     The output signal PC of the buffer circuit  17   b  is also supplied to buffer circuits  17   c  to  17   f  and the output signals of the buffer circuits  17   c  to  17   f  are supplied to the gates of switching transistors Tr 4  to Tr 7 , respectively. The respective buffer circuits  17   c  to  17   f  turn off the respective transistors Tr 4  to Tr 7  in response to a stop signal PC having the L level, respectively.  
         [0063]     The output terminal of the boosting power supply generation circuit  21  is connected to the power supply Vcc via the transistor Tr 4  and the output terminal of the deboosting power supply generation circuit  22  is connected to the power supply Vcc via the transistor Tr 5 . The output terminal of the precharge power supply generation circuit  23  is connected to the power supply Vss via the transistor Tr 6  and the substrate potential generation circuit  15  is connected to the power supply Vss via the transistor Tr 7 .  
         [0064]     When a stop signal PC having the H level is supplied to the external terminal  14   a , each of the boosting power supply generation circuit  21 , deboosting power supply generation circuit  22 , precharge power supply generation circuit  23  and substrate potential generation circuit  15  stops its operation and each of the transistors Tr 4  to Tr 7  is turned on. Thereupon, the output signals of the boosting power supply generation circuit  21  and deboosting power supply generation circuit  22  are fixed to the level of the power supply Vcc and the output terminals of the precharge power supply generation circuit  23  and substrate potential generation circuit  15  are fixed to the level of the power supply Vss.  
       Fourth Embodiment  
       [0065]      FIG. 10  is a schematic circuit diagram of a conventional reference potential generation circuit  500  which is provided in a memory circuit and one of the internal power supply generation circuits. The reference potential generation circuit  500  consumes D.C. during normal operation.  
         [0066]     In the reference potential generation circuit  500 , the power supply voltage Vcc is supplied to the sources of P-channel MOS (PMOS) transistors Tr 8  and Tr 9 . The gates of the PMOS transistors Tr 8  and Tr 9  are connected to each other and connected to the drain of the PMOS transistor Tr 9 .  
         [0067]     The drain of the PMOS transistor Tr 8  is connected to the drain of an N-channel MOS (NMOS) transistor Tr 10  and connected to the gates of the NMOS transistor Tr 10  and an NMOS transistor Tr 11 . The drain of the PMOS transistor Tr 9  is connected to the drain of the NMOS transistor Tr 11 . The sources of the NMOS transistors Tr 10  and Tr 11  are connected to the power supply Vss.  
         [0068]     A PMOS transistor Tr 12  is connected in parallel to the NMOS transistor Tr 9  and a stop signal /PC is supplied to the gate of the PMOS transistor Tr 12 . An NMOS transistor Tr 13  is connected in parallel to the NMOS transistor Tr 10  and a stop signal PC is supplied to the gate of the NMOS transistor Tr 13 .  
         [0069]     In the reference potential generation circuit  500 , when the stop signal PC has the L level, a power supply Vcc and a power supply Vss are supplied, each of the transistors Tr 8  to Tr 11  is turned on and a predetermined reference voltage Vref is generated at the drain (a node N 2 ) in accordance with the on-resistance of the transistors Tr 8  to Tr 11 . In this state, a drain current flows in the PMOS transistor Tr 8  and the NMOS transistor Tr 10  and a drain current flows in the PMOS transistor Tr 9  and the NMOS transistor Tr 11 , thereby consuming the predetermined D.C.  
         [0070]     When the stop signal PC goes high, the transistors Tr 12  and Tr 13  are turned on. Thereupon, the gate potentials of the PMOS transistors Tr 8  and Tr 9  are set to substantially the level of power supply Vcc and the PMOS transistors Tr 8  and Tr 9  are turned off. At the same time, the gates potential of the NMOS transistors Tr 10  and Tr 11  are set to substantially the level of power supply Vss and the NMOS transistors Tr 10  and Tr 11  are turned off. As a result, the reference potential generation circuit  500  enters the stop mode, stops the operation and cuts off D.C.  
         [0071]     However, the reference potential generation circuit  500  does not operate normally if the stop signal PC is switched from the H level to the L level (even if the normal mode is returned to from the stop mode). That is, even if the transistors Tr 12  and Tr 13  are switched from the ON state to the OFF state, the transistors Tr 8  to Tr 11  are kept in the OFF state and the predetermined reference voltage Vref is not generated. Accordingly, to reset the stop mode of the reference potential generation circuit  500 , the power supply Vcc and the power supply Vss need to be provided again after they have been cut off once.  
         [0072]      FIG. 11  is a schematic circuit diagram of a reference voltage generation circuit  520  according to a fourth embodiment of the present invention in which the stop mode can move to the normal mode without turning on the power again.  
         [0073]     The reference voltage generation circuit  520  comprises an NMOS transistor Tr 14  connected in parallel to the NMOS transistor Tr 11 . A start signal PU is supplied to the NMOS transistor Tr 14 .  
         [0074]      FIG. 12 ( a ) is a schematic circuit diagram of a start signal generation circuit  24  which generates the start signal PU from the stop signal PC. in the start signal generation circuit  24 , the stop signal PC is supplied to the first input terminal of an AND circuit  25  via four inverter circuits  7   d . The stop signal PC is also supplied to the second input terminal of the AND circuit  25  via an inverter circuit  7   e . The start signal PU is output from the AND circuit  25 . That is, as shown in  FIG. 12 ( b ), when the stop signal PC falls from the H level to the L level, the start signal PU having an H-level pulse width that corresponds to the difference between the operation delay time of the inverter circuits  7   d  and the operation delay time of the inverter circuit  7   e  is generated. When the stop signal PC is fixed to the H level or the L level or when the stop signal PC rises from the L level to the H level, the start signal PU is maintained at the L level.  
         [0075]     When the stop signal PC falls from the H level to the L level and the normal mode is returned from the stop mode, the start signal PU, which stays high for a predetermined period of time, is supplied to the NMOS transistor Tr 14 . Thereupon, the transistor Tr 14  is turned on and the transistors Tr 8  and Tr 9  are turned on. Subsequently, the transistors Tr 10  and Tr 11  are turned on and the reference voltage Vref is generated. Thus, the reference voltage generation circuit  520  is automatically restarted without again turning on the power supply Vcc and the power supply Vss when the stop mode moves to the normal mode.  
       Fifth Embodiment  
       [0076]      FIG. 13  is a schematic circuit diagram of a conventional data transfer circuit  270  provided in a memory circuit. In the data transfer circuit  270 , an input signal IN is supplied to a first latch circuit  27   a  via a transfer gate  26   a , the latch signal of the latch circuit  27   a  is provided to a second latch circuit  27   b  via a transfer gate  26   b , then an output signal OUT is output from the second latch circuit  27   b.    
         [0077]     A clock signal φ is supplied to the gate of the P-channel transistor of the transfer gate  26   a  and the gate of the N-channel transistor of the transfer gate  26   b . A clock signal /φ is supplied to the gate of the N-channel transistor of the transfer gate  26   a  and the gate of the P-channel transistor of the transfer gate  26   b.    
         [0078]     The input terminal of the latch circuit  27   b  is connected to the power supply Vss via the NMOS transistor Tr 15  and a reset signal RST is supplied to the gate of the transistor Tr 15 .  
         [0079]      FIG. 14 ( a ) is a schematic circuit diagram of a power-on reset circuit  50  which generates the reset signal RST when a power supply Vcc and a power supply Vss are provided. Resistors R 2  and R 3  and an NMOS transistor Tr 18  are connected in series between the power supplies Vcc and Vss and a node N 3  between the resistors R 2  and R 3  is connected to the gate of the NMOS transistor Tr 16 .  
         [0080]     The drain (a node N 4 ) of an NMOS transistor Tr 16  is connected to the power supply Vss via a resistor R 4  and the source of the NMOS transistor Tr 16  is connected to the power supply Vss via an NMOS transistor Tr 19 . A stop signal /PC is supplied to the gates of the NMOS transistors Tr 18  and Tr 19 .  
         [0081]     The node N 4  is connected to the input terminal of an inverter circuit  7   f  and the output signal of the inverter circuit  7   f  is output via an inverter circuit  7   g  as the reset signal RST.  
         [0082]     In the power-on reset circuit  50 , in the normal mode in which the stop signal /PC is set to the H level, as shown in  FIG. 14 ( b ), when the power supply Vcc and the power supply Vss are provided, the potential of the nodes N 3  and N 4 , i.e., the reset signal RST rises together with the level of power supply Vcc. When the potential difference between the node N 3  and the power supply Vss exceeds the threshold of the NMOS transistor Tr 16 , the transistor Tr 16  is turned on and the node N 4  is set to substantially the level of the power supply Vss, then the reset signal RST is immediately set to the L level.  
         [0083]     Thus, when the power supply Vcc and the power supply Vss are provided, the power-on reset circuit  50  generates the reset signal RST that is a pulse signal which rises together with the power supply Vcc and falls to the L level when the voltage of the power supply Vss exceeds the threshold of the NMOS transistor Tr 16 .  
         [0084]     In the power-on reset circuit  50 , in the stop mode in which a stop signal PC is set to the H level, a stop signal /PC is set to the L level and the NMOS transistors Tr 18  and Tr 19  are turned off. Thereupon, the D.C. flowing in the resistors R 2  and R 3  and the D.C. flowing from the resistor R 4  to the NMOS transistor Tr 16  are cut off and the nodes N 3  and N 4  are set to the level of power supply Vcc, then the reset signal RST is set to the H level. In the stop mode, although the reset signal RST is fixed to the H level in this manner, there is no hindrance in the operation of a memory circuit.  
         [0085]     In the normal mode, an input signal IN is sequentially transferred to the latch circuits  27   a  and  27   b  by the inversion of clock signals φ and /φ and an output signal OUT is output from the latch circuit  27   b . Further, when the power is provided, the NMOS transistor Tr 15  is temporarily turned on and the output signal OUT is reset to the H level by the reset signal RST.  
         [0086]     However, in the conventional data transfer circuit  270 , when the normal mode is switched to the stop mode, the output signal OUT output from the data transfer circuit  270  may become indefinite. Specifically, in the stop mode, the clock signal φ is fixed to the L level and the clock signal /φ is fixed to the H level. Thereupon, the transfer gate  26   a  is fixed to the electrically conducted state and the transfer gate  26   b  is fixed to the electrically non-conducted state and the latch circuit  27   a  latches the input signal IN immediately before the normal mode is switched to the stop mode.  
         [0087]     When the normal mode is returned from the stop mode, the latched data of the latch circuit  27   a  is output as an output signal OUT via the transfer gate  26   b  and the latch circuit  27   b  due to the inversion operation of the clock signals φ and /φ. Thus, the output signal OUT is indefinite.  
         [0088]      FIG. 15  is a schematic circuit diagram of a data transfer circuit  280  according to a fifth embodiment of the present invention. The data transfer circuit  280  comprises the NMOS transistor Tr 17  connected in parallel to the NMOS transistor Tr 15  and a start signal PU is supplied to the gate of the NMOS transistor Tr 17 .  
         [0089]     In such data transfer circuit  280 , when the normal mode is switched from the stop mode, the transistor Tr 17  is temporarily turned on in response to the start signal PU from the start signal generation circuit  24  and the output signal OUT of the latch circuit  27   b  is reset to the H level. Accordingly, when the normal mode is switched from the stop mode, since an indefinite output signal OUT is not output from the latch circuit  27   b , the circuit at the back stage that receives the output signal OUT operates normally.  
       Sixth Embodiment  
       [0090]      FIG. 16  is a schematic circuit diagram of a reset circuit  600  according to a sixth embodiment of the present invention. The reset circuit  600  comprises the power-on reset circuit  50  and a composite reset signal generation circuit  60  which generates a composite reset signal RSTS by logically combining the reset signal RST from the power-on reset circuit  50  and the start signal PU of the start signal generation circuit  24 .  
         [0091]     The composite reset signal generation circuit  60  includes a NOR circuit  29  which generates a logical composite signal by receiving the reset signal RST generated in the power-on reset circuit  50  and the start signal PU generated in the start signal generation circuit  24  and an inverter circuit  7   h  which receives the logical composite signal from the NOR circuit  29  and generates a composite reset signal RSTS. The composite reset signal RSTS is set to the H level when at least either the reset signal RST or the start signal PU is set to the H level.  
         [0092]     The composite reset signal RSTS is supplied to the gate of the transistor Tr 15  of the data transfer circuit  270  of  FIG. 13 . In the data transfer circuit  270 , the output signal OUT of the latch circuit  27   b  is reset to the H level in accordance with the composite reset signal RSTS when the power supply Vcc and the power supply Vss are provided and when the normal mode is switched from the stop mode. Accordingly, by using the composite reset signal RSTS, the transistor Tr 17  of the data transfer circuit  280  of  FIG. 15  and the wiring for supplying a start signal PU to the gate of the transistor Tr 17  are unnecessary. As a result, the number of elements and wiring of the memory circuit  12  comprising a plurality of data transfer circuits are reduced.  
         [0093]     In the sixth embodiment, as shown in  FIG. 17 , the stop signal PC supplied from the external terminal  14   a  may also be supplied to the NOR circuit  29  instead of the start signal PU.  
         [0094]     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.