Abstract:
A semiconductor device includes plural memory cell blocks, each having a memory array of plural memory cells. Plural control circuits are provided in correspondence with each of the memory cell blocks, for writing information to the memory cell blocks and for reading information written in the memory cell blocks. Plural input/output terminals are for inputting the information to be written and for outputting the information to be read. Plural multiplexers are provided in correspondence with each of the input/output terminals, for conveying the information to be written from the input/output terminals and for conveying the information to be read to the input/.output terminals. A bidirectional transfer type buffer is connected to each connection line between the control circuits and the multiplexers, for selectively conveying information from the control circuits to each of the multiplexers and for selectively conveying information from the multiplexers to each of the control circuits.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-293504, filed on Oct. 30, 2006, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device, and in particular, to the field of data transfer technology in memory. 
   2. Description of the Related Art 
   There are increasing demands for a semiconductor memory with improved integration density and speed as well as enhanced capacity. For example, a pseudo static RAM (PSRAM) for use in mobile phones is expected to reach the 256- to 512-Mbit size from the currently used 128-Mbit size. Conventionally, in order to meet the demands for enhanced capacity, improving the integration density enables reduction of memory chip area as well as improved speed in memory chips. 
   However, as the recent increase in integration density, wiring resistance also increases in chips, which has prohibited improvements in chip speed. 
   Therefore, Patent Document 1 (Japanese Patent Laid-Open No. 3222545) discloses an invention for improving speed of memory in chips. In the invention disclosed in Patent Document 1, plural memory cell brocks as sub-arrays are formed, and each system between each of the memory cell blocks and I/O terminals is independent from one another. That is, memory cell blocks A and B are formed and input/output terminals A and B are provided corresponding to each memory cell block. One system ranging from memory cell block A to an input/output terminal A, and another system ranging from memory cell block B to an input/output terminal B, are completely independent from each other. Only data input from the input/output terminal A can be written in the memory cell block A for writing data to the memory cell block A, and data can only be output to the input/output terminal A for reading data from the memory cell block A. Similarly, only data input from the input/output terminal B can be written in the memory cell block B for writing data to the memory cell block B, and data can only be output to the input/output terminal B for reading data from the memory cell block B. 
   As such, in the system of the invention described in Patent Document 1 has a following problem. Specifically, the system may be formed as a multi-chip package of a combination of a controller and memory. In this case, a pad used in memory may be changed depending on the type of controller. However, it is extremely difficult to change the pad being used due to the one-to-one correspondence between each memory cell block and each input/output terminal. 
   SUMMARY OF THE INVENTION 
   A semiconductor device in accordance with one aspect of the present invention comprises: two or more memory cell blocks, each of which has a memory cell array of a plurality of memory cells; a plurality of control circuits, which are provided in correspondence with each of the memory cell blocks, for writing information to the memory cell blocks and for reading information written in the memory cell blocks; a plurality of input/output terminals for inputting the information to be written and for outputting the information to be read; a plurality of multiplexers, which are provided in correspondence with each of the input/output terminals, for conveying the information to be written from the input/output terminals and for conveying the information to be read to the input/output terminals; and a bidirectional transfer type buffer, which is connected to each connection line between the control circuits and the multiplexers, for selectively conveying information from the control circuits to each of the multiplexers and for selectively conveying information from the multiplexers to each of the control circuits. 
   In addition, a semiconductor device in accordance with one aspect of the present invention comprises: two or more memory cell blocks, each of which has a memory cell array of a plurality of memory cells; a plurality of control circuits, which are provided in correspondence with each of the memory cell blocks, for writing information to the memory cell blocks; a plurality of input terminals for inputting the information to be written; a plurality of multiplexers, which are provided in correspondence with each of the input terminals, for conveying the information input from the input terminals; and a bidirectional transfer type buffer, which is connected to each connection line between the control circuit and the multiplexer, for selectively conveying information from the multiplexers to each of the control circuits. 
   In addition, a semiconductor device in accordance with one aspect of the present invention comprises: two or more memory cell blocks, each of which has a memory cell array of a plurality of memory cells; a plurality of control circuits, which are provided in correspondence with each of the memory cell blocks, for reading information written in the memory cell blocks; a plurality of output terminals for outputting the information to be read; a plurality of multiplexers, which are provided in correspondence with each of the output terminals, for conveying the information to be read to the output terminals; and a bidirectional transfer type buffer, which is connected to each connection line between the control circuits and the multiplexers, for selectively conveying information from the control circuits to each of the multiplexers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a configuration diagram of a semiconductor device in accordance with a first embodiment; 
       FIG. 2  is a configuration diagram illustrating essential parts of the semiconductor device in accordance with the first embodiment; 
       FIG. 3  illustrates a read operation ( 1 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 4  illustrates a read operation ( 2 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 5  illustrates a read operation ( 3 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 6  illustrates a read operation ( 4 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 7  illustrates a write operation ( 1 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 8  illustrates a write operation ( 2 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 9  illustrates a write operation ( 3 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 10  illustrates a write operation ( 4 ) of the semiconductor device in accordance with the first embodiment; 
       FIG. 11  is a configuration diagram of a semiconductor device in accordance with a second embodiment; 
       FIG. 12  is a configuration diagram illustrating essential parts of the semiconductor device in accordance with the second embodiment; 
       FIG. 13  illustrates a read operation ( 1 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 14  illustrates a read operation ( 2 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 15  illustrates a read operation ( 3 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 16  illustrates a read operation ( 4 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 17  illustrates a write operation ( 1 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 18  illustrates a write operation ( 2 ) of the semiconductor device in accordance with the second embodiment; 
       FIG. 19  illustrates a write operation ( 3 ) of the semiconductor device in accordance with the second embodiment; and 
       FIG. 20  illustrates a write operation ( 4 ) of the semiconductor device in accordance with the second embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   An embodiment of the present invention will now be described below. 
   First Embodiment 
     FIG. 1  illustrates a pseudo static RAM (PSRAM)  10  in accordance with this embodiment. The pseudo static RAM (PSRAM)  10  of this embodiment has a control-signal input terminal  11  for inputting control signals from outside, which is conveyed to a control-signal control circuit  12 . In the control-signal control circuit  12 , a control signal is generated based on the input control signal to control each of memory cell blocks A  14  and B  24  via a row-column control circuit  13 . 
   In addition, input and output of data in the pseudo static RAM (PSRAM)  10  of this embodiment are performed through an input/output terminal A  19  and an input/output terminal B  29 . The input/output terminals A  19  and B  29  are connected to their corresponding input/output circuits A  18  and B  28  through a DQa line and a DQb line, respectively, while the input/output circuits A  18  and B  28  are connected to their corresponding read-write multiplexers A  17  and B  27  through a DQINOUTa line and a DQINOUTb line, respectively. 
   The read-write multiplexers A  17  and B  27  are connected to their corresponding control circuits of this embodiment, i.e., secondary sense amplifiers/write drivers A  15  and B  25  through an RWDa line and an RWDb line, respectively. In addition, a bidirectional transfer type buffer  16  is provided between, and also connected to, the RWDa line (a connection line between the read-write multiplexer A  17  and the secondary sense amplifier/write driver A  15 ) and the RWDb line (a connection line between the read-write multiplexer B  27  and the secondary sense amplifier/write driver B  25 ). 
   Next, the bidirectional transfer type buffer  16  will be described in detail based on  FIG. 2 .  FIG. 2  illustrates a peripheral configuration of the bidirectional transfer type buffer  16  in the pseudo static RAM (PSRAM)  10  illustrated in  FIG. 1 . 
   The bidirectional transfer type buffer  16  of this embodiment comprises two transfer circuits  30   a  and  30   b . The transfer circuit  30   a  has a function of transferring information from the RWDa line to the RWDb line. The transfer circuit  30   b  has a function of transferring information from the RWDb line to the RWDa line. The output terminal of one of the transfer circuits  30   a  and  30   b  is connected to the input terminal of the other of these transfer circuits, and vice versa. 
   In each transfer circuit  30   a  and  30   b , drains of a p-type transistor  31   a  and an n-type transistor  32   a  are connected to each other, and drains of a p-type transistor  31   b  and an n-type transistor  32   b  are connected to each other, thereby forming each output terminal of the transfer circuits  30   a  and  30   b , respectively. Each output terminal of NAND circuits  33   a  and  33   b  is connected to each gate of the p-type transistors  31   a  and  31   b , respectively. In addition, each output terminal of NOR circuits  34   a  and  34   b  is connected to each gate of the n-type transistors  32   a  and  32   b , respectively. One input terminal of each of the NAND circuits  33   a  and  33   b  and one input terminal of each of the NOR circuits  34   a  and  34   b  are connected to each other, thereby forming each input terminal of the transfer circuits  30   a  and  30   b , respectively. That is, each information from the connection lines RWDa and RWDb is input to the one input terminal of each of the NAND circuits  33   a  and  33   b  and the one input terminal of each of the NOR circuits  34   a  and  34   b . In addition, the other input terminal of each of the NAND circuits  33   a  and  33   b  and the other input terminal of each of the NOR circuits  34   a  and  34   b  via inverters  35   a  and  35   b  are connected to each other, and each input terminal is connected to each input terminal for control signals CTL 0  and CTL 1 , respectively. That is, control signals CTL 0  and CTL 1  are input to the other input terminal of each of the NAND circuits  33   a  and  33   b , while inverted signals of the control signals CTL 0  and CTL 1  are input to the other input terminal of each of the NOR circuits  34   a  and  34   b.    
   In addition, the output terminal of the transfer circuit  30   a , which is configured by a connection point between the drains of the p-type transistor  31   a  and the n-type transistor  32   a , is connected to the input terminal of the transfer circuit  30   b . The input terminal of the transfer circuit  30   b  is formed by connecting one input terminal of the NAND circuit  33   b  to one input terminal of the NOR circuit  34   b . The input terminal of the transfer circuit  30   b  is also connected to the connection line RWDb between the secondary sense amplifier/write driver B  25  and the read-write multiplexer B  27 . In addition, a data retaining circuit  36   a  is provided for the connection line RWDb. 
   On the other hand, the output terminal of the transfer circuit  30   b , which is configured by a connection point between the drains of the p-type transistor  31   b  and the n-type transistor  32   b , is connected to the input terminal of the transfer circuit  30   a . The input terminal of the transfer circuit  30   a  is formed by connecting one input terminal of the NAND circuit  33   a  to one input terminal of the NOR circuit  34   a . The input terminal of the transfer circuit  30   a  is also connected to the connection line RWDa between the secondary sense amplifier/write driver A  15  and the read-write multiplexer A  17 . In addition, a data retaining circuit  36   b  is provided for the connection line RWDa. 
   Next, a reading method in the pseudo static RAM (PSRAM)  10  of this embodiment will be described. 
   As illustrated in  FIG. 3 , when information stored in the memory cell block A  14  is read via the input/output terminal A  19 , the information does not need to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information read from the memory cell block A  14  is conveyed to the secondary sense amplifier/write driver A  15 . Thereafter, the bidirectional transfer type buffer  16  would not operate since the CTL 0  remains “L” when information is conveyed to the connection line RWDa, to which the secondary sense amplifier/write driver A  15 , the read-write multiplexer A  17  and the bidirectional transfer type buffer  16  are connected, and the information in the connection line RWDa is conveyed to the connection line DQINOUTa via the read-write multiplexer A  17 . The information is then conveyed to the connection line DQa via the input/output circuit A  18  and output from the input/output terminal A  19 . In this case, the information is conveyed directly from the secondary sense amplifier/write driver A  15  to the read-write multiplexer A  17 . 
   As illustrated in  FIG. 4 , when information stored in the memory cell block A  14  is read by the input/output terminal B  29 , the information needs to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information read from the memory cell block A  14  is conveyed to the secondary sense amplifier/write driver A  15 . Thereafter, upon the information being conveyed to the connection line RWDa, to which the secondary sense amplifier/write driver A  15 , the read-write multiplexer A  17  and the bidirectional transfer type buffer  16  are connected, the CTL 0  turns to “H”. Accordingly, the information in the connection line RWDa is conveyed to the connection line RWDb via the bidirectional transfer type buffer  16 . Then, the information conveyed to the connection line RWDb is further conveyed to the connection line DQINOUTb via the read-write multiplexer B  27  and subsequently to the DQb line via the input/output circuit B  28 , after which it is output from the input/output terminal B  29 . 
   As illustrated in  FIG. 5 , when information stored in the memory cell block B  24  is read by the input/output terminal B  29 , the information does not need to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information read from the memory cell block B  24  is conveyed to the secondary sense amplifier/write driver B  25 . Thereafter, the bidirectional transfer type buffer  16  would not operate since the CTL 1  remains “L” when the information is conveyed to the connection line RWDb, to which the secondary sense amplifier/write driver B  25 , the read-write multiplexer B  27  and the bidirectional transfer type buffer  16  are connected, and the information in the connection line RWDb is conveyed to the connection line DQINOUTb via the read-write multiplexer B  27  and subsequently to the connection line DQb via the input/output circuit B  28 , after which it is output from the input/output terminal B  29 . In this case, the information is conveyed directly from the secondary sense amplifier/write driver B  25  to the read-write multiplexer B  27 . 
   As illustrated in  FIG. 6 , when information stored in the memory cell block B  24  is read by the input/output terminal A  19 , the information needs to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information read from the memory cell block B  24  is conveyed to the secondary sense amplifier/write driver B  25 . Thereafter, upon the information being conveyed to the connection line RWDb, to which the secondary sense amplifier/write driver B  25 , the read-write multiplexer B  27  and the bidirectional transfer type buffer  16  are connected, the CTL 1  turns to “H”. Accordingly, the information in the connection line RWDb is conveyed to the connection line RWDa via the bidirectional transfer type buffer  16 . Then, the information conveyed to the connection line RWDa is further conveyed to the connection line DQINOUTa via the read-write multiplexer A  17  and subsequently to the connection line DQa via the input/output circuit A  18 , after which it is output from the input/output terminal A  19 . 
   Next, a writing method in the pseudo static RAM (PSRAM)  10  of this embodiment will be described. 
   As illustrated in  FIG. 7 , when the information input from the input/output terminal A  19  is written in the memory cell block A  14 , the information does not need to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information input from the input/output terminal A  19  is conveyed to the connection line DQa and then to the connection line DQINOUTa via the input/output circuit A  18 . The information conveyed to the connection line DQINOUTa is further conveyed via the read-write multiplexer A  17  to the connection line RWDa, to which the read-write multiplexer A  17 , the secondary sense amplifier/write driver A  15  and the bidirectional transfer type buffer  16  are connected. At this moment, the bidirectional transfer type buffer  16  would not operate since the CTL 0  remains “L”, and the input information is conveyed to the secondary sense amplifier/write driver A  15  and then written in a memory cell in a predetermined region of the memory cell block A  14 . In this case, the information is conveyed directly from the read-write multiplexer A  17  to the secondary sense amplifier/write driver A  15 . 
   As illustrated in  FIG. 8 , when the information input from the input/output terminal A  19  is written in the memory cell block B  24 , the information needs to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information input from the input/output terminal A  19  is conveyed to the connection line DQa and then to the connection line DQINOUTa via the input/output circuit A  18 . The information conveyed to the connection line DQINOUTa is further conveyed via the read-write multiplexer A  17  to the connection line RWDa, to which the read-write multiplexer A  17 , the secondary sense amplifier/write driver A  15  and the bidirectional transfer type buffer  16  are connected. At this moment, the CTL 0  turns to “H” and the information conveyed to the connection line RWDa is further conveyed to the connection line RWDb via the bidirectional transfer type buffer  16 . Then, the information conveyed to the connection line RWDb is further conveyed to the secondary sense amplifier/write driver B  25  and written in a memory cell in a predetermined region of the memory cell block B  24 . 
   As illustrated in  FIG. 9 , when the information input from the input/output terminal B  29  is written in the memory cell block B  24 , the information does not need to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information input from the input/output terminal B  29  is conveyed to the connection line DQb and then to the connection line DQINOUTb via the input/output circuit B  28 . The information conveyed to the connection line DQINOUTb is further conveyed via the read-write multiplexer B  27  to the connection line RWDb, to which the read-write multiplexer B  27 , the secondary sense amplifier/write driver B  25  and the bidirectional transfer type buffer  16  are connected. At this moment, the bidirectional transfer type buffer  16  would not operate since the CTL 1  remains “L”, and the input information is conveyed to the secondary sense amplifier/write driver B  25  and then written in a memory cell in a predetermined region of the memory cell block B  24 . In this case, the information is conveyed directly from the read-write multiplexer B  27  to the secondary sense amplifier/write driver B  25 . 
   As illustrated in  FIG. 10 , when the information input from the input/output terminal B  29  is written in the memory cell block A  14 , the information needs to be conveyed via the bidirectional transfer type buffer  16 . Thus, the information input from the input/output terminal B  29  is conveyed to the connection line DQb and then to the connection line DQINOUTb via the input/output circuit B  28 . The information conveyed to the connection line DQINOUTb is further conveyed via the read-write multiplexer B  27  to the connection line RWDb, to which the read-write multiplexer B  27 , the secondary sense amplifier/write driver B  25  and the bidirectional transfer type buffer  16  are connected. At this moment, the CTL 1  turns to “H” and the information conveyed to the connection line RWDb is further conveyed to the connection line RWDa via the bidirectional transfer type buffer  16 . Then, the information conveyed to the connection line RWDa is further conveyed to the secondary sense amplifier/write driver A  15  and written in a memory cell in a predetermined region of the memory cell block A  14 . 
   From the above description, when reading information in the cases of  FIG. 4  and  FIG. 6 , although it is necessary to transfer data from the connection line RWDa to the connection line RWDb, or vice versa, the bidirectional transfer type buffer  16  enables even small circuits to provide high-speed data transfer. In addition, in the cases of  FIG. 3  and  FIG. 5 , it is not necessary to transfer data from the connection line RWDa to the connection line RWDb, or vice versa, and thus information can be read, without intervention by the bidirectional transfer type buffer  16 , by keeping both the CTL 0  and the CTL 1  at an “L” state so that power consumption may be reduced. 
   In addition, when writing information in the cases of  FIG. 8  and  FIG. 10 , it is necessary to transfer data from the connection line RWDa to the connection line RWDb, or vice versa, the bidirectional transfer type buffer  16  enables even small circuits to provide high-speed data transfer. In addition, in the cases of  FIG. 7  and  FIG. 9 , it is not necessary to transfer data from the connection line RWDa to the connection line RWDb, or vice versa, and thus information can be read, without intervention by the bidirectional transfer type buffer  16 , by keeping both the CTL 0  and the CTL 1  at an “L” state so that power consumption may be reduced. 
   The bidirectional transfer type buffer  16  described above enables output of data, which is read from the memory cell block A or the memory cell block B, to any of the input/output terminal A or the input/output terminal B in a small-sized and high-speed configuration with reduced power consumption. Similarly, it also enables writing of data, which is input from the input/output terminal A or the input/output terminal B, to any of the memory cell block A or the memory cell block B. 
   Meanwhile, the pseudo static RAM (PSRAM)  10  of this embodiment may be any semiconductor memory such as DRAM, SRAM or flash memory. 
   Second Embodiment 
     FIG. 11  illustrates a pseudo static RAM (PSRAM)  50  in accordance with this embodiment. The pseudo static RAM (PSRAM)  50  of this embodiment has a control-signal input terminal  51  for inputting control signals from outside, which are conveyed to a control-signal control circuit  52 . In the control-signal control circuit  52 , a control signal is generated based on the input control signal to control each of memory cell blocks A  54  and B  64  via a row-column control circuit  53 . 
   In addition, input and output of data in the pseudo static RAM (PSRAM)  50  of this embodiment are performed through an input/output terminal A  59  and an input/output terminal B  69 . The input/output terminals A  59  and B  69  are connected to their corresponding input/output circuits A  58  and B  68  through a DQa line and a DQb line, respectively. In addition, the input/output circuit A  58  is connected to a read-write multiplexer A  57  through a connection line DQINa for writing and a connection line DQOUTa for reading, while the input/output circuit B  68  is connected to a read-write multiplexer B  67  through a connection line DQINb for writing and a connection line DQOUTb for reading. 
   The read-write multiplexers A  57  and B  67  are connected to their corresponding control circuits of this embodiment, i.e., secondary sense amplifiers/write drivers A  55  and B  65  through each connection line WDa and WDb for writing and each connection line RDa and RDb for reading, respectively. In addition, a “W” bidirectional transfer type buffer  66  is provided between, and also connected to, the connection line WDa (a connection line for writing between the read-write multiplexer A  57  and the secondary sense amplifier/write driver A  55 ) and the connection line WDb (a connection line for writing between the read-write multiplexer B  67  and the secondary sense amplifier/write driver B  65 ). On the other hand, an “R” bidirectional transfer type buffer  56  is provided between, and also connected to, the connection line RDa (a connection line for reading between the read-write multiplexer A  57  and the secondary sense amplifier/write driver A  55 ) and the connection line RDb (a connection line for reading between the read-write multiplexer B  67  and the secondary sense amplifier/write driver B  65 ). 
   Next, the “R” bidirectional transfer type buffer  56  and the “W” bidirectional transfer type buffer  66  will be described in detail based on  FIG. 12 .  FIG. 12  illustrates a peripheral configuration of the “R” bidirectional transfer type buffer  56  and the “W” bidirectional transfer type buffer  66  in the pseudo static RAM (PSRAM)  50  illustrated in  FIG. 11 . 
   The “R” bidirectional transfer type buffer  56  of this embodiment comprises two transfer circuits  70   a  and  70   b . The transfer circuit  70   a  has a function of transferring information from the RDa line to the RDb line. The transfer circuit  70   b  has a function of transferring information from the RDb line to the RDa line. The output terminal of one of the transfer circuits  70   a  and  70   b  is connected to the input terminal of the other of these transfer circuits, and vice versa. 
   In each transfer circuit  70   a  and  70   b , drains of a p-type transistor  71   a  and an n-type transistor  72   a  are connected to each other, and drains of a p-type transistor  71   b  and an n-type transistor  72   b  are connected to each other, thereby forming each output terminal of the transfer circuits  70   a  and  70   b , respectively. Each output terminal of NAND circuits  73   a  and  73   b  is connected to each gate of the p-type transistors  71   a  and  71   b , respectively. In addition, each output terminal of NOR circuits  74   a  and  74   b  is connected to each gate of the n-type transistors  72   a  and  72   b . One input terminal of each of the NAND circuits  73   a  and  73   b  and one input terminal of each of the NOR circuits  74   a  and  74   b  are connected to each other, thereby forming each input terminal of the transfer circuits  70   a  and  70   b , respectively. That is, each information from the connection lines RDa and RDb is input to the one input terminal of each of the NAND circuits  73   a  and  73   b  and the one input terminal of each of the NOR circuits  74   a  and  74   b . In addition, the other input terminal of each of the NAND circuits  73   a  and  73   b  and the other input terminal of each of the NOR circuits  74   a  and  74   b  via inverters  75   a  and  75   b  are connected to each other, and each input terminal is connected to each input terminal for control signals RDCTL 0  and RDCTL 1 , respectively. That is, control signals RDCTL 0  and RDCTL 1  are input to the other input terminal of each of the NAND circuits  73   a  and  73   b , while inverted signals of the control signals RDCTL 0  and RDCTL 1  are input to the other input terminal of each of the NOR circuits  74   a  and  74   b.    
   In addition, the output terminal of the transfer circuit  70   a , which is configured by a connection point between the drains of the p-type transistor  71   a  and the n-type transistor  72   a , is connected to the input terminal of the transfer circuit  70   b . The input terminal of the transfer circuit  70   b  is formed by connecting one input terminal of the NAND circuit  73   b  to one input terminal of the NOR circuit  74   b . The input terminal of the transfer circuit  70   b  is also connected to the connection line RDb between the secondary sense amplifier/write driver B  65  and the read-write multiplexer B  67 . In addition, a data retaining circuit  76   a  is provided for the connection line RWDb. 
   On the other hand, the output terminal of the transfer circuit  70   b , which is configured by a connection point between the drains of the p-type transistor  71   b  and the n-type transistor  72   b , is connected to the input terminal of the transfer circuit  70   a . The input terminal of the transfer circuit  70   a  is formed by connecting one input terminal of the NAND circuit  73   a  to one input terminal of the NOR circuit  74   a , and it is also connected to the connection line RDa between the secondary sense amplifier/write driver A  55  and the read-write multiplexer A  57 . A data retaining circuit  76   b  is provided for the connection line RDa. 
   In addition, the “W” bidirectional transfer type buffer  66  comprises two transfer circuits  80   a  and  80   b . The transfer circuit  80   a  has a function of transferring information from the WDa line to the WDb line. The transfer circuit  70   b  has a function of transferring information from the WDb line to the WDa line. The output terminal of one of the transfer circuits  80   a  and  80   b  is connected to the input terminal of the other of these transfer circuits, and vice versa. 
   In each transfer circuit  80   a  and  80   b , drains of a p-type transistor  81   a  and an n-type transistor  82   a  are connected to each other, and drains of a p-type transistor  81   b  and an n-type transistor  82   b  are connected to each other, thereby forming each output terminal of the transfer circuits  80   a  and  80   b , respectively. Each output terminal of NAND circuits  83   a  and  83   b  is connected to each gate of the p-type transistors  81   a  and  81   b , respectively. In addition, each output terminal of NOR circuits  84   a  and  84   b  is connected to each gate of the n-type transistors  82   a  and  82   b . One input terminal of each of the NAND circuits  83   a  and  83   b  and one input terminal of each of the NOR circuits  84   a  and  84   b  are connected to each other, thereby forming each input terminal of the transfer circuits  80   a  and  80   b , respectively. That is, each information from the connection lines WDa and WDb is input to the one input terminal of each of the NAND circuits  83   a  and  83   b  and the one input terminal of each of the NOR circuits  84   a  and  84   b . In addition, the other input terminal of each of the NAND circuits  83   a  and  83   b  and the other input terminal of each of the NOR circuits  84   a  and  84   b  via inverters  85   a  and  85   b  are connected to each other, and each input terminal is connected to each input terminal for control signals WDCTL 0  and WDCTL 1 , respectively. That is, control signals WDCTL 0  and WDCTL 1  are input to the other input terminal of each of the NAND circuits  83   a  and  83   b , while inverted signals of the control signals WDCTL 0  and WDCTL 1  are input to the other input terminal of each of the NOR circuits  84   a  and  84   b.    
   In addition, the output terminal of the transfer circuit  80   a , which is configured by a connection point between the drains of the p-type transistor  81   a  and the n-type transistor  82   a , is connected to the input terminal of the transfer circuit  80   b . The input terminal of the transfer circuit  80   b  is formed by connecting one input terminal of the NAND circuit  83   b  to one input terminal of the NOR circuit  84   b , and it is also connected to the connection line WDb between the secondary sense amplifier/write driver B  65  and the read-write multiplexer B  67 . A data retaining circuit  86   a  is provided for the connection line WDb. 
   On the other hand, the output terminal of the transfer circuit  80   b , which is configured by a connection point between the drains of the p-type transistor  81   b  and the n-type transistor  82   b , is connected to the input terminal of the transfer circuit  80   a . The input terminal of the transfer circuit  80   a  is formed by connecting one input terminal of the NAND circuit  83   a  to one input terminal of the NOR circuit  84   a , and it is also connected to the connection line WDa between the secondary sense amplifier/write driver A  55  and the read-write multiplexer A  57 . A data retaining circuit  86   b  is provided for the connection line WDa. 
   Next, a reading method in the pseudo static RAM (PSRAM)  50  of this embodiment will be described. 
   As illustrated in  FIG. 13 , when information stored in the memory cell block A  54  is read by the input/output terminal A  59 , the information does not need to be conveyed via the “R” bidirectional transfer type buffer  56 . Thus, the information read from the memory cell block A  54  is conveyed to the secondary sense amplifier/write driver A  55 . Thereafter, the “R” bidirectional transfer type buffer  56  would not operate since the RDCTL 0  remains “L” when information is conveyed to the connection line RDa, to which the secondary sense amplifier/write driver A  55 , the read-write multiplexer A  57  and the “R” bidirectional transfer type buffer  56  are connected, and the information conveyed to the connection line RDa is further conveyed to the connection line DQOUTa via the read-write multiplexer A  57 . The information is then conveyed to the connection line DQa via the input/output circuit A  58  and output from the input/output terminal A  59 . In this case, the information is conveyed directly from the secondary sense amplifier/write driver A  55  to the read-write multiplexer A  57 . 
   As illustrated in  FIG. 14 , when information stored in the memory cell block A  54  is read by the input/output terminal B  69 , the information needs to be conveyed via the “R” bidirectional transfer type buffer  56 . Thus, the information read from the memory cell block A  54  is conveyed to the secondary sense amplifier/write driver A  55 . Thereafter, upon the information being conveyed to the connection line RDa, to which the secondary sense amplifier/write driver A  55 , the read-write multiplexer A  57  and the “R” bidirectional transfer type buffer  56  are connected, the RDCTL 0  turns to “H”. Accordingly, the information in the connection line RDa is conveyed to the connection line RDb via the “R” bidirectional transfer type buffer  56 . Then, the information conveyed to the connection line RDb is further conveyed to the connection line DQOUTb via the read-write multiplexer B  67  and subsequently to the connection line DQb via the input/output circuit B  68 , after which it is output from the input/output terminal B  69 . 
   As illustrated in  FIG. 15 , when information stored in the memory cell block B  64  is read by the input/output terminal B  69 , the information does not need to be conveyed via the “R” bidirectional transfer type buffer  56 . Thus, the information read from the memory cell block B  64  is conveyed to the secondary sense amplifier/write driver B  65 . Thereafter, the “R” bidirectional transfer type buffer  56  would not operate since the RDCTL 1  remains “L” when the information is conveyed to the connection line RDb, to which the secondary sense amplifier/write driver B  65 , the read-write multiplexer B  67  and the “R” bidirectional transfer type buffer  56  are connected, and the information conveyed to the connection line RDb is further conveyed to the connection line DQOUTb via the read-write multiplexer B  67  and subsequently to the connection line DQb via the input/output circuit B  68 , after which it is output from the input/output terminal B  69 . In this case, the information is conveyed directly from the secondary sense amplifier/write driver B  65  to the read-write multiplexer B  67 . 
   As illustrated in  FIG. 16 , when information stored in the memory cell block B  64  is read by the input/output terminal A  59 , the information needs to be conveyed via the “R” bidirectional transfer type buffer  56 . Thus, the information read from the memory cell block B  64  is conveyed to the secondary sense amplifier/write driver B  65 . Thereafter, upon the information being conveyed to the connection line RDb, to which the secondary sense amplifier/write driver B  65 , the read-write multiplexer B  67  and the “R” bidirectional transfer type buffer  56  are connected, the RDCTL 1  turns to “H”. Accordingly, the information in the connection line RDb is conveyed to the connection line RDa via the “R” bidirectional transfer type buffer  56 . Then, the information conveyed to the connection line RDa is further conveyed to the connection line DQOUTa via the read-write multiplexer A  57  and subsequently to the connection line DQa via the input/output circuit A  58 , after which it is output from the input/output terminal A  59 . 
   Next, a writing method in the pseudo static RAM (PSRAM)  50  of this embodiment will be described. 
   As illustrated in  FIG. 17 , when the information input from the input/output terminal A  59  is written in the memory cell block A  54 , the information does not need to be conveyed via the “W” bidirectional transfer type buffer  66 . Thus, the information input from the input/output terminal A  59  is conveyed to the connection line DQa and then to the connection line DQINa via the input/output circuit A  58 . The information conveyed to the connection line DQINa is further conveyed via the read-write multiplexer A  57  to the connection line WDa, to which the read-write multiplexer A  57 , the secondary sense amplifier/write driver A  55  and the “W” bidirectional transfer type buffer  66  are connected. At this moment, the “W” bidirectional transfer type buffer  66  would not operate since the WDCTL 0  remains “L”, and the input information is conveyed to the secondary sense amplifier/write driver A  55  and then written in a memory cell in a predetermined region of the memory cell block A  54 . In this case, the information is conveyed directly from the read-write multiplexer A  57  to the secondary sense amplifier/write driver A  55 . 
   As illustrated in  FIG. 18 , when the information input from the input/output terminal A  59  is written in the memory cell block B  64 , the information needs to be conveyed via the “W” bidirectional transfer type buffer  66 . Thus, the information input from the input/output terminal A  59  is conveyed to the connection line DQa and then to the connection line DQINa via the input/output circuit A  58 . The information conveyed to the connection line DQINa is further conveyed via the read-write multiplexer A  57  to the connection line WDa, to which the read-write multiplexer A  57 , the secondary sense amplifier/write driver A  55  and the “W” bidirectional transfer type buffer  66  are connected. At this moment, the WDCTL 0  turns to “H” and the information conveyed to the connection line WDa is further conveyed to the connection line WDb via the “W” bidirectional transfer type buffer  66 . Then, the information conveyed to the connection line WDb is further conveyed to the secondary sense amplifier/write driver B  65  and written in a memory cell in a predetermined region of the memory cell block B  64 . 
   As illustrated in  FIG. 19 , when the information input from the input/output terminal B  69  is written in the memory cell block B  64 , the information does not need to be conveyed via the “W” bidirectional transfer type buffer  66 . Thus, the information input from the input/output terminal B  69  is conveyed to the connection line DQb and then to the connection line DQINb via the input/output circuit B  68 . The information conveyed to the connection line DQINb is further conveyed via the read-write multiplexer B  67  to the connection line WDb, to which the read-write multiplexer B  67 , the secondary sense amplifier/write driver B  65  and the “W” bidirectional transfer type buffer  66  are connected. At this moment, the W bidirectional transfer type buffer  66  would not operate since the WDCTL 1  remains “L”, and the input information is conveyed to the secondary sense amplifier/write driver B  65  and then written in a memory cell in a predetermined region of the memory cell block B  64 . In this case, the information is conveyed directly from the read-write multiplexer B  67  to the secondary sense amplifier/write driver B  65 . 
   As illustrated in  FIG. 20 , when the information input from the input/output terminal B  69  is written in the memory cell block A  54 , the information needs to be conveyed via the “W” bidirectional transfer type buffer  66 . Thus, the information input from the input/output terminal B  69  is conveyed to the connection line DQb and then to the connection line DQINb via the input/output circuit B  68 . The information conveyed to the connection line DQINb is further conveyed via the read-write multiplexer B  67  to the connection line WDb, to which the read-write multiplexer B  67 , the secondary sense amplifier/write driver B  65  and the “W” bidirectional transfer type buffer  66  are connected. At this moment, the WDCTL 1  turns to “H” and the information conveyed to the connection line WDb is further conveyed to the connection line WDa via the “W” bidirectional transfer type buffer  66 . Then, the information conveyed to the connection line WDa is further conveyed to the secondary sense amplifier/write driver A  55  and written in a memory cell in a predetermined region of the memory cell block A  54 . 
   From the above description, when reading information in the cases of  FIG. 14  and  FIG. 16 , although it is necessary to transfer data from the connection line RDa to the connection line RDb, or vice versa, the “R” bidirectional transfer type buffer  56  enables even small circuits to provide high-speed data transfer. In addition, in the cases of  FIG. 13  and  FIG. 15 , it is not necessary to transfer data from the connection line RDa to the connection line RWDb, or vice versa, and thus information can be read, without intervention by the “R” bidirectional transfer type buffer  56 , by keeping both the RDCTL 0  and the RDCTL 1  at an “L” state so that power consumption may be reduced. 
   In addition, when writing information in the cases of  FIG. 18  and  FIG. 20 , it is necessary to transfer data from the connection line WDa to the connection line WDb, or vice versa, the “W” bidirectional transfer type buffer  66  enables even small circuits to provide high-speed data transfer. In addition, in the cases of  FIG. 17  and  FIG. 19 , it is not necessary to transfer data from the connection line WDa to the connection line WDb, or vice versa, and thus information can be read, without intervention by the “W” bidirectional transfer type buffer  66 , by keeping both the WDCTL 0  and the WDCTL 1  at an “L” state so that power consumption may be reduced. 
   The “R” bidirectional transfer type buffer  56  and the “W” bidirectional transfer type buffer  66  enables output of data, which is read from the memory cell block A or the memory cell block B, to any of the input/output terminal A or the input/output terminal B in a small-sized and high-speed configuration with reduced power consumption. Similarly, it also enables writing of data, which is input from the input/output terminal A or the input/output terminal B, to any of the memory cell block A or the memory cell block B. 
   Meanwhile, the pseudo static RAM (PSRAM)  50  of this embodiment may be any semiconductor memory such as DRAM, SRAM or flash memory. 
   Although the semiconductor device of the present invention has been described in detail with reference to embodiments thereof, the present invention is not limited to those embodiments described above, and it may take other forms than described and illustrated herein.