Patent Abstract:
To provide a semiconductor memory for synchronizing input of a command except for POWER-DOWN-EXIT or the like and write or read of data with an external clock and generating a column operation synchronous pulse having the same number as that of a burst length within the semiconductor memory by using an internal operation synchronous pulse having this external clock as a trigger and after activation of a column system circuit, using the internal operation synchronous pulse as a trigger. This semiconductor memory uses column pulse transfer signals, which are different between read and write to control a column system circuit.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-268359, filed Sep. 22, 1999, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor memory, for example, a semiconductor memory to synchronize input of a command and write or read of data with an external clock, such as a synchronous DRAM. 
     In the case of semiconductor memory which synchronizes input of a command and write or read of data with an external clock, the operation of circuits in a chip is synchronized with some basic pulses, which are generated within the chip by using the external clock as a trigger. In such a semiconductor memory, an access time from input of read command to data output is determined by the number of pulses in the external synchronous clock. For example, in a synchronous DRAM, the number of the pulses in the external synchronous clock is called as CAS latency (CL) and it is important value for a specification. A column operation synchronous pulse, which is synchronized with the operation of the column system circuit within a chip, is generated at a timing to fill this value. Further, the timing of this column operation synchronous pulse is usually determined uniquely by the above CL. The same pulse can be used even if a column command represents “read” or “write”, since the pulse control is advantageously simplified when the column operation synchronous pulses of read and write are identical. 
     FIGS. 1 to  3  illustrate the above described conventional semiconductor memory, respectively. FIG. 1 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in the synchronous DRAM. FIG. 2 is a circuit diagram showing a constitutional example of an input column address latch controller in the circuit shown in FIG.  1 . FIG. 3 is a circuit diagram showing a column pulse transfer controller in the circuit shown in FIG.  1 . 
     As shown in FIG. 1, a circuit in reference to the control of the column system basic pulse in the synchronous DRAM comprises an external clock input buffer  11 , pulse generators  12 - 1 ,  12 - 2 ,  13 - 1 ,  13 - 2 , delay circuits  14 - 1 ,  14 - 2 , a CAS input buffer  15 , a RAS input buffer  16 , a CS input buffer  17 , a decoder  18 , a decoder and latch circuit  19 , a WE input buffer  20 , an input column address latch controller  21 , address input buffers  22 - 1 ,  22 - 2  (ADD 1 , ADD 2 ), address latches  23 - 1 ,  23 - 2 , core buses  24 - 1 ,  24 - 2  (addresses K 1 , K 2 ), a burst length counter  25 , a column pulse transfer controller  26 , a column bank controller  27 , a DQ buffer  28 , a data line  29 , an off chip driver  30 , an output pulse generator  31 , transfer gates  32 - 1  to  32 - 7 ,  32 - 9  to  32 - 12 , a column address decoder  33 , a memory cell allay  34  and an inverter  35  or the like. 
     As shown in FIG. 2, the above column address latch controller  21  is composed of a NAND gate  41 , a transfer gate  42  and inverters  43 ,  44 ,  45 . 
     Further, as shown in FIG. 3, the above column pulse transfer controller  26  is composed of a NOR gate  51 , transfer gates  52  to  54  and inverters  55  to  60 . A signal CL 2 OPN controls the transfer gate  52  to open the transfer gate  52  when the CAS latency is  2 . A signal CL 3 OPN controls the transfer gate  53  to open the transfer gate  52  when the CAS latency is  3 . 
     In FIGS. 1 to  3 , in order to simplify the illustrations, it is shown that only one-sided MOS transistor gates of transfer gates  32 - 1  to  32 - 7 ,  32 - 9  to  32 - 12 ,  42 ,  52  to  54  are provided with signals. However, other sided MOS transistor gates are provided with inverted ones of the above signals. Here, the transfer gates  32 - 1  to  32 - 7 ,  32 - 9  to  32 - 12 ,  42 ,  52  to  54  are formed by connecting a current path of a P channel type MOS transistor and a current path of an N channel type MOS transistor in parallel. 
     In this example, two kinds of column system basic pulses are used for a column operation synchronization and a column address latch. These two kinds of column system basic pulses are activated at the same timing. 
     FIGS. 4 and 5 are timing charts for showing signal waveforms of the CL 2  and the CL 3  schematically. FIG. 4 shows a signal waveform in the case that the CL 2 , i.e., the CAS latency is  2  and FIG. 5 shows a signal waveform in the case that the CL 3 , i.e., the CAS latency is  3 , respectively. 
     As shown in FIG. 1, the external clock input buffer  11  is connected to two pulse generators  12 - 1  and  13 - 1 . As shown in the timing chart of FIG. 4, respective pulse generators  12 - 1  and  13 - 1  generate pulse signals Pa and Pb, which have different pulse widths each other, from leading edges of an external clock VCLK. These respective pulse generators  12 - 1  and  13 - 1  are connected to pulse generators  12 - 2  and  13 - 2  via delay circuits  14 - 1  and  14 - 2 , which are composed identically, respectively. These pulse generators  12 - 2  and  13 - 2  generate pulse signals Pa′ and Pb′ from edges of the above pulse signals Pa and Pb, respectively. The pulse generators  12 - 1 ,  13 - 1  and  12 - 2 ,  13 - 2  are identically composed. The pulse signals Pa′, Pb′ are obtained by shifting the pulse signals Pa, Pb for a certain period of time, respectively. In the present example, as described later, it is assumed that the pulse signals Pb, Pb′ are used for the column operation synchronous pules and the pulse signals Pa, Pa′ are mainly used for the column address latch pulse. 
     If the column access information is inputted from a command pin, a decoder  18  is connected to the CAS input buffer  15 , the RAS input buffer  16  and the CS input buffer  17 , respectively, to decode these signals and generate a column system activated signal Pc. Further, the decoder and the latch circuit  19  is connected to the WE input buffer  20  in addition to the CAS input buffer  15 , the RAS input buffer  16  and the CS input buffer  17 . If the inputted command is write, the decoder and the latch circuit  19  activates a write enable signal Pe. If the inputted command is read, it activates a read enable signal Pf, respectively. 
     When the column system activated signal Pc is activated, the input column address latch controller  21  outputs a column address entry pulse Pd. This pulse Pd opens the transfer gates  32 - 6  and  32 - 7 . Therefore, the address information of the address input buffers  22 - 1  and  22 - 2  are transferred to the address latches  23 - 1  and  23 - 2  in a column address counter  39 , so that addresses K 1  and K 2  of the core buses  24 - 1  and  24 - 2  are decided. 
     On the other hand, activation of the column system activated signal Pc allows the burst length counter  25  to be activated. The pulse signal Pb counts up the activated burst length counter  25  by number of times corresponding to the burst length. During this time, the activated burst length counter  25  is activating a burst operation activated signal Pg. 
     As understood from the circuit construction shown in FIG. 3, in the case that the CAS latency is  2 (CL 2 ), the column pulse transfer controller  26  activates a column pulse transfer signal Pj soon after the burst operation activated signal Pg is activated. This column pulse transfer signal Pj opens the transfer gates  32 - 3  and  32 - 4  to transfer the pulse signal Pa′ to the column bank controller  27  as a column operation synchronous pulse Pp and transfer the pulse signal Pb′ to the address latches  23 - 1  and  23 - 2  in a column address counter  39  as a column address latch pulse Pq. At this time, by the inverter  35 , a inverted signal of the above column address latch pulse Pq is also transferred to the address latches  23 - 1  and  23 - 2 . 
     In the present example, there is a margin in the activating timing of the column pulse transfer signal Pj with respect to the timing for activating these pulse signals Pa′ and Pb′. Therefore, finding a logical OR of the column system activated signal Pc and the burst operation activated signal Pg, the column pulse transfer signal Pj is generated. 
     Using the column operation synchronous pulse Pp as a trigger, the column bank controller  27  generates a write pulse Pl when the write enable signal Pe is active and generates a read pulse Pm when the read enable signal Pf is active. The write pulse Pl opens a write gate of the DQ buffer  28  in a memory cell portion MCA. As a result, it becomes possible to write into the memory cell allay  34 . Further, the read pulse Pm opens a read gate of the above DQ buffer  28  to output a cell data Pn to the data line  29 . The cell data Pn of the above data line  29  is transferred to the off chip driver  30 . After inputting a command, if the external clock VCLK at second cycles becomes active, the output pulse generator  31  outputs an output pulse Po by using the activated external clock VCLK as a trigger. This output pulse Po opens the transfer gate  32 - 5 , which is arranged on the output terminal of the off chip driver  30 . Then, an output data Dout is outputted to catch up with the external clock VCLK at third cycles. 
     On the other hand, while the column address latch pulse Pq, which is activated at the same time as the column operation synchronous pulse Pp, has been generated, the transfer gates  32 - 10  and  32 - 12  as backward registers are closed. The transfer gates  32 - 10  and  32 - 12  are located within the address latches  23 - 1  and  23 - 2  in the column address counter  39 . During read and write operation to the memory cell portion MCA as the column operation synchronous pulse Pp as a trigger, the core bus addresses K 1  and K 2  are latched. The column operation synchronous pulse Pp is generated at the same time as the column address latch pulse Pq. Further, at the same time, the transfer gates  32 - 9  and  32 - 11  as forward registers are opened and the address information at a single digit before is recorded in this register. Hereby, the information of the address latch  23 - 1  is transferred to the address latch  23 - 2 . If the pulse Pq is deactivated, the transfer gates  32 - 10  and  32 - 12  as the backward registers are opened to output the recorded address information at a single digit before to the core buses  24 - 1  and  24 - 2 . 
     In the case of CL 3 , as understandably from the timing chart in FIG. 5, the burst operation activated signal Pg turns to a column pulse transfer signal Ph with being delayed by one cycle by the pulse signal Pb at the register within the column pulse transfer controller  26 . In other words, the pulse signals Pa and Pb are transferred as the column operation synchronous pulse Pp and the column address latch pulse Pq with being delayed from the command input by one cycle, so that the access to the memory cell portion MCA is also delayed from the command input by one cycle and the date is outputted to catch up with the external clock VCLK at fourth cycle. 
     Next, the case that the write command is interrupted during the read operation of the CL 2  and the CL 3  is considered. As shown in FIG. 4, in the case of the CL 2 , upon inputting the write command, latches of the core bus addresses K 1  and K 2  due to the column address latch pulse Pq are released. Accordingly, the latching of the address is the same as that upon normal input of commands. On the contrary, in the case of the CL 3 , as shown in FIG. 5, when the write command is inputted, the core bus addresses K 1  and K 2  are latched in response to the column address latch pulse Pq. Therefore, the addresses ADD 1  and ADD 2  are latched from the address input buffers  22 - 1  and  22 - 1  to be held in the address latches  23 - 1  and  23 - 3  within the counter at once. Then, after the column address latch pulse Pq is inactive, the addresses ADD 1  and ADD 2  are outputted to the core buses  24 - 1  and  24 - 2 . 
     As described above, using the same column operation synchronous pulse in read and write, there is a merit such that a system for latching the address when the column command interrupts during the column burst operation. 
     In the mean time, in the above described conventional synchronous DRAM, as shown in FIGS. 6 and 7, after the completion of the write burst, the case that a precharge command is inputted at the next cycle. FIG. 6 is a timing chart illustrating the operation in the case that the CAS latency is  2 (CL 2 ) and FIG. 7 is a timing chart illustrating the operation in the case that the CAS latency is  3 (CL 3 ). Here, a time from writing by the write pulse Pm to resetting of the word line WL is determined as tWR. The time from input of the precharge command to the word line reset is not changed in the CL 2  and the CL 3 . On the other hand, the timing of the column operation synchronous pulse is uniquely determined by the CAS latency, which is important for determining a timing of the read operation. In other words, even when the column command is read or write, in the column operation synchronous pulse, the CL 3  is delayed than the CL 2 . Therefore, if the CAS latency is  3  (CL 3 ), tWR is smaller than in the case where the CAS latency is  2  (CL 2 ). Consequently, a word line WL is reset before the data is completely written into a memory cell immediately before precharging. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a semiconductor memory, which is capable of sufficiently securing an operational margin of a column system circuit. 
     The object of the present invention is attained by a semiconductor memory for synchronizing at least a part of input of a command and write or read of data with an external clock and generating a column operation synchronous pulse having the same number as that of a burst length within the semiconductor memory by using an internal operation synchronous pulse having the external clock as a trigger and after inputting a column system command, using the internal operation synchronous pulse as a trigger comprising a first path to which a first column operation synchronous pulse is transferred during read; a second path to which a second column operation synchronous pulse, which is different from the first column operation synchronous pulse, is transferred during write; and a switching circuit for selectively switching the first path and the second path. 
     Further, the object of the present invention is attained by a semiconductor memory for synchronizing input of a command and write or read of data with an external clock and generating a column operation synchronous pulse having the same number as that of a burst length within the semiconductor memory by using an internal operation synchronous pulse having the external clock as a trigger and after inputting a column system command, using the internal operation synchronous pulse as a trigger comprising a first pulse generator for generating a first column operation synchronous pulse for read within a chip with an external clock as a trigger; a second pulse generator for generating a second column operation synchronous pulse for read within a chip with the external clock as a trigger; a first signal line provided with a first column operation synchronous pulse for read to be outputted from the first pulse generator during read; a second signal line provided with a second column operation synchronous pulse for write to be outputted from the second pulse generator during read; and a column pulse transfer controller for controlling transfer of a first column operation synchronous pulse from the first pulse generator to the first signal line and transfer of a second column operation synchronous pulse from the second pulse generator to the second signal line, respectively. 
     Still further, the object of the present invention is attained by a synchronous DRAM comprising a first pulse generator for generating a first column operation synchronous pulse for read within a chip with an external clock as a trigger; a second pulse generator for generating a second column operation synchronous pulse for read within a chip with the external clock as a trigger; a first signal line provided with a first column operation synchronous pulse for read to be outputted from the first pulse generator during read; a second signal line provided with a second column operation synchronous pulse for write to be outputted from the second pulse generator during read; a first transfer gate to be arranged between the first pulse generator and the first signal line; a second transfer gate to be arranged between the second pulse generator and the second signal line; and a column pulse transfer controller for controlling the first and second transfer gate and controlling transfer of a first column operation synchronous pulse from the first pulse generator to the first signal line and transfer of a second column operation synchronous pulse from the second pulse generator to the second signal line, respectively. 
     In the semiconductor memory of the present invention, which has the above configurations, the timing of a synchronous pulse can be adjusted in conformity to a limiting factor to secure sufficiently an operational margin of a column system circuit, since a column operation synchronous pulses, which are different between read and write, is used. Hence, if the CAS latency is  3 , tWR is smaller than in the case where the CAS latency is  2 . Consequently, so that a problem such that a word line is reset before the data is completely written into a memory cell immediately before precharging is avoided. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in a synchronous DRAM to explain with respect to a conventional semiconductor memory; 
     FIG. 2 is a circuit diagram showing a constitutional example of an input column address latch controller in the circuit shown in FIG. 1 to explain with respect to a conventional semiconductor memory; 
     FIG. 3 is a circuit diagram showing a column pulse transfer controller in the circuit shown in FIG. 1 to explain with respect to a conventional semiconductor memory; 
     FIG. 4 is a timing chart showing respective signal waveforms typically in the case that the CAS latency is  2  in the semiconductor memory shown in FIGS. 1 to  3 ; 
     FIG. 5 is a timing chart showing respective signal waveforms typically in the case that the CAS latency is  3  in the semiconductor memory shown in FIGS. 1 to  3 ; 
     FIG. 6 is a timing chart illustrating the operation in the case that the CAS latency is  2 ; 
     FIG. 7 is a timing chart illustrating the operation in the case that the CAS latency is  3 ; 
     FIG. 8 is a block diagram showing a construction of a synchronous DRAM schematically to explain with respect to a semiconductor memory according to a first embodiment of the present invention; 
     FIG. 9 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in a synchronous DRAM to explain with respect to a semiconductor memory according to a first embodiment of the present invention; 
     FIG. 10 is a circuit diagram showing a constitutional example of an input write address latch controller in the circuit shown in FIG. 9 to explain with respect to a first embodiment of the present invention; 
     FIG. 11 is a circuit diagram showing a constitutional example of a column pulse transfer controller in the circuit shown in FIG. 9 to explain with respect to a first embodiment of the present invention; 
     FIG. 12 is a timing chart showing respective signal waveforms typically in the case that a write command interrupts during the read operation when the CAS latency is  3  in the semiconductor memory shown in FIGS. 9 to  11 ; and 
     FIG. 13 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in a synchronous DRAM to explain with respect to a semiconductor memory according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 8 to  11  illustrate a semiconductor memory according to a first embodiment of the present invention, respectively. FIG. 8 is a block diagram schematically showing a construction of a synchronous DRAM. FIG. 9 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in this synchronous DRAM. FIG. 10 is a circuit diagram showing a constitutional example of an input write address latch controller in the circuit shown in FIG.  9 . FIG. 11 is a circuit diagram showing a constitutional example of a column pulse transfer controller in the circuit shown in FIG.  9 . In FIGS. 8 to  11 , the identical reference numerals are given to the elements, which correspond to the elements in FIGS. 1 to  3 . 
     As shown in FIG. 8, the memory cell allay in this synchronous DRAM is divided into four banks, namely, banks MCA- 1  to MCA- 4 . Respective banks MCA- 1  to MCA- 4  are composed of memory cell allays  34 - 1  to  34 - 4 , CSL drivers  40 - 1  to  40 - 4 , DQ buffers  28 - 1  to  28 - 4 , and circuit blocks  50 - 1  to  50 - 4  each having column address decoder and controller or the like, respectively. 
     Further, corresponding to the above respective banks MCA- 1  to MCA- 4 , column bank controllers  27 - 1  to  27 - 4  are provided, respectively. The column bank controllers  27 - 1  to  27 - 4  controlled DQ buffers  28 - 1  to  28 - 4  provided in the banks MCA- 1  to MCA- 4 . Commands CMD are inputted to CAS input buffer  15 , RAS input buffer  16 , CS input buffer  17  and WE input buffer  20  via command pads  62 . A decoder and latch  19  is connected to the input buffers  15 ,  16 ,  17  and  20 , and latching and decoding the commands CMD. The decoder and latch  19  controlling the each column bank controllers  27 - 1  to  27 - 4 . Address signals S ADD  are inputted to column address counter  39  via address pads  63  and address input buffers  22 . Each column address decoders provided in the circuit blocks  50 - 1  to  50 - 4  connected to receive the output signals (core bus addresses K 1  and K 2 ) of the column address counter  39 . The DQ buffers  28 - 1  to  28 - 4  in the above respective banks MCA- 1  to MCA- 4  are intended to be inputted with a data S DATA  from a data input/output pads  64  via data lines  29 , respectively or the data outputted from the DQ buffers  28 - 1  to  28 - 4  are intended to be outputted to the outside via the data lines  29 , off chip drivers (OCD.)  30  and the data input/output pads  64 . Further external clock VCLK inputted in the clock input pad  65  supplied with column pulse generator  66  via an external input buffer  11 . Each column bank controllers  27 - 1  to  27 - 4  connected to receive column operation synchronous pulses Ppr and Ppw generated by the column pulse generator  66 . 
     As shown in FIG. 9, the circuit in reference to the control of the column system basic pulse in a synchronous DRAM is composed of the external clock input buffer  11 , pulse generators  12 - 1 ,  12 - 2 ,  12 - 3 ,  13 - 1  and  13 - 2 , delay circuits  14 - 1 ,  14 - 2 , the CAS input buffer  15 , the RAS input buffer  16 , the CS input buffer  17 , a decoder  18 , the decoder and latch circuit  19 , the WE input buffer  20 , an input column address latch controller  21 , address input buffers  22 - 1 ,  22 - 2 , address latches  23 - 1 ,  23 - 2 , core buses  24 - 1 ,  24 - 2  (addresses K 1 , K 2 ), a burst length counter  25 , a column pulse transfer controller  26 ′, the column bank controller  27 , the DQ buffer  28 , a data line  29 , an off chip driver  30 , an output pulse generator  31 , transfer gates  32 - 1  to  32 - 8 , a column address decoder  33 , the memory cell allay  34 , an inverter  35 , an input write address latch controller  36 , an AND gate  37  and signal lines  38 - 1 ,  38 - 2  or the like. 
     The circuit shown in FIG. 9 is composed of a pulse generator  12 - 3 , a transfer gate  32 - 8 , a signal line  38 - 1  for transferring a column operation synchronous pulse Ppr for read, a signal line  38 - 2  for transferring a column operation synchronous pulse Ppw for write, an input write address latch controller  36  and an AND gate  37  or the like in addition to the conventional circuit shown in FIG.  1 . 
     In other words, according to the present invention, the column operation synchronous pulse (internal operation synchronous pulse) into a write only pulse and a read only pulse. In this embodiment, an example of a method using different column operation synchronous pulse in a read operation and a write operation, respectively, despite of CAS latency (CL), a write operation is performed at a conventional timing that the CAS latency is  2 (CL 2 ). 
     The above pulse generator  12 - 3  is connected to the delay circuit  14 - 1  in parallel with the pulse generator  12 - 2 . This pulse generator  12 - 3  generates a pulse signal Pa′w to be activated by the same timing as that of the pulse signal Pa′. The pulse signal Pa is transferred to the signal line  38 - 1  as a column operation synchronous pulse Ppr for read in response to the column pulse transfer signal Ph generated by the column pulse transfer controller  26 ′ during a read operation when the CAS latency is  3 (CL 3 ). The pulse signal Pa′w generated by the pulse generator  12 - 3  is transferred to the signal line  38 - 2  as a column operation synchronous pulse Ppw for write in response to the transfer signal Pjw despite of the CAS latency. Further, a pulse signal Pa′r is transferred to the signal line  38 - 1  as a column operation synchronous pulse Ppr for read by a read column pulse transfer signal Pjr when the CAS latency is  2 (CL 2 ). The pulse Pa′w is transferred to the signal line  38 - 2  as the column operation synchronous pulse Ppw for write by the transfer signal Pjw to be generated by the column pulse transfer controller  26 ′ during a write operation. 
     Further, the column pulse transfer controller  26 ′ is provided with a write input pulse Pr to be outputted from the WE input buffer  20 , a write enable signal Pe and a read enable signal Pf in addition to the pulse signal Pb to be outputted from the above pulse generator  13 - 1 , the column system activated signal Pc to be outputted form the above decoder  18  and the burst operation activated signal Pg to be outputted from the above burst length counter  25 . Further, the column pulse transfer controller  26 ′ is intended to output the pulse signal Ph for controlling the above transfer gates  32 - 1  and  32 - 2 , a column pulse transfer signal Pjr for read for controlling the above transfer gate  32 - 3 , a column pulse transfer signal Pjw for write for controlling the above transfer gate  32 - 8  and a column pulse transfer signal Pja for controlling the above transfer gate  32 - 4 . 
     As shown in FIG. 10, the above input write address latch controller  36  is comprised of a NAND gate  71 , a transfer gate  72  and inverters  73 ,  74  and  75 . A write column address entry pulse Ps is outputted from the input write address latch controller  36  to be provided to one input terminals of the AND gate  37 . Then, the write column address entry pulse Ps releases latches of the core bus addresses K 1  and K 2  in the address latches  23 - 1  and  23 - 2  by the column address latch pulse Pq. 
     Further, as shown in FIG. 11, the above column pulse transfer controller  26 ′ is composed of AND gates  81  to  83 , NAND gates  84  to  89 , an OR gate  90 , a transfer gate  91  and inverters  92  to  96 . This column pulse transfer controller  26 ′ basically comprises two flip-flop latch circuits. Upon inputting the column command at the CL 2  or inputting a write command at the CL 3 , the above flip-flop latch circuit activates an output signal Pj′ of the NAND gate  86  from the column system activated signal Pc to latch the activated output signal Pj′ with the burst operation activated signal Pg. When the burst operation is completed, the latch is released with the signal SC and the output signal Pj′ of the NAND gate  86  is deactivated. The above signal SC is a negative pulse to be generated at completion of the burst operation. Here, the explanation thereof is omitted. During the read operation, a signal Pjr is generated from the output signal Pj′ of the NAND gate  86  and during the write operation, the transfer signal Pjw is generated from the output signal Pj′ of the NAND gate  86 . During write and read operation, a signal Pja is generated from the output signal Pj′ of the NAND gate  86 . On the other hand, the flip-flop circuit at the lower column activates the output the pulse signal Ph′ of the NAND gate  88  from the column system activated signal Pc upon inputting the read command at the CL 3  to latch the activated output signal Ph′ with the burst operation activated signal Pg. When the transfer gate  91  is opened due to deactivation of the pulse signal Pb, the signal Ph′ is changed into the signal Ph at one cycle&#39;s delay. Further, in the CL 3 , as well as in the CL 2 , after the burst operation is completed, the latch is released by the signal SC and the output signal Ph′ is deactivated. In this state, the transfer gate  91  is opened by deactivation of the pulse signal Pb, so that the column pulse transfer signal Ph is deactivated at one cycle&#39;s delay. 
     The above column pulse transfer controller  26 ′ has a system such that the latch of the output signal Ph′ of the NAND gate  88  is released by the signal SA and the latch of the output signal Pj′ of the NAND gate  86  is released. When the read interrupts during the write burst at the CL 3  or when the write interrupts during the read burst at the CL 3 , the column pulse transfer controller  26 ′ is capable of switching the output signal Ph′ of the NAND gate  88  to the output signal Pj′ of the NAND gate  86 . 
     In FIGS. 9 to  11 , in order to simplify the illustrations, it is shown that only one sided MOS transistor gates of transfer gates  32 - 1  to  32 - 8 ,  72 ,  91  are provided with signals. However, other sided MOS transistor gates are provided with inverted ones of the above signals. Further, the CL 2 ACT and the CL 3 ACT in FIG. 11 are signals to be activated at the CL 2  and the CL 3 , respectively. 
     Next, with reference to a timing chart in FIG. 12, the operation of the synchronous DRAM having the above described construction is explained below. 
     FIG. 12 is the timing chart showing the write interruption during the read burst operation at the CL 3 . Using the above described column synchronous pulse system, during the write interruption during the read burst at the CL 3 , the address informations ADD 1  and ADD 2  in the address input buffers  22 - 1  and  22 - 2  are latched, so that the latches of the address latches  23 - 1  and  23 - 2  of the core buses  24 - 1  and  24 - 2  should be released. 
     In the present embodiment, only upon inputting the write command, the core bus address latch mask pulse Psis activated at the same time of the column address entry pulse Pd. Then, the activated core bus address latch mask pulse Ps masks the column address latch pulse Pq to output the addresses ADD 1  and ADD 2  to the core buses  24 - 1  and  24 - 2 . The above pulse Ps is generated by the input write address latch controller  36  (see FIG.  10 ). This controller  36  is composed of the write input pulse Pr in addition to the input signal of the input column address latch controller  21  for generating the column address entry pulse Pd. The logic configurations of the input write address latch controller  36  and the input column address latch controller  21  are substantially identical and they are activated at the approximately same timing. Therefore, at the same time that the input write address latch controller  36  opens the transfer gates  32 - 10  and  32 - 12  and entries the addresses ADD 1  and ADD 2 , the latch state of the address latches  23 - 1  and  23 - 2  are released. As a result, the entry addresses ADD 1  and ADD 2  are transferred to the core buses  24 - 1  and  24 - 2  at the same timing as that of a normal command input. 
     According to the above configurations, since a column operation synchronous pulses, which are different between read and write, is used, the semiconductor memory of the present invention is capable of adjusting a timing of a synchronous pulse in conformity to a limiting factor to secure sufficiently an operational margin of a column system circuit. Thus, in the case that the CAS latency is  3 , tWR is smaller compared with the case that the CAS latency is  2 , so that a problem such that a word line is reset in the course that writing into a memory cell just before precharging is not sufficient is avoided. 
     FIG. 13 is a block diagram showing extractively a circuit in reference to the control of a column system basic pulse in a synchronous DRAM to explain with respect to a semiconductor memory according to a second embodiment of the present invention. According to the above first embodiment, the output signal of the delay circuit  14 - 1  is provided to the pulse generators  12 - 2  and  12 - 3 . On the contrary, according to the present embodiment, the delay circuit  14 - 3  is further arranged and the output signal of this delay circuit  14 - 3  is provided to the pulse generator  12 - 2  so that the output signal of the above delay circuit  14 - 1  is provided to the pulse generator  12 - 3 . In addition, the delay circuit  14 - 4 , the pulse generator  13 - 3  and the transfer gate  32 - 13  are further arranged. 
     According to the above construction, the same operation as that of the circuit shown in FIG. 9 is performed to basically obtain the same effect as that of the circuit shown in FIG.  9 . 
     As explained above, according to the present invention, a semiconductor memory such that the operational margin of the column system circuit can be sufficiently secured. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Technology Classification (CPC): 7