Patent Publication Number: US-2022215892-A1

Title: Nonvolatile memory including on-die-termination circuit and storage device including the nonvolatile memory

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/161,995 filed Jan. 29, 2021, which is a continuation of U.S. patent application Ser. No. 16/862,624 filed Apr. 30, 2020, issued as U.S. Pat. No. 11,024,400 on Jun. 1, 2021, which is a continuation of U.S. patent application Ser. No. 16/458,933 filed Jul. 1, 2019, issued as U.S. Pat. No. 10,559,373 on Feb. 11, 2020, which is a continuation of U.S. patent application Ser. No. 16/426,391 filed May 30, 2019, issued as U.S. Pat. No. 10,679,717 on Jun. 9, 2020, which is a continuation of U.S. patent application Ser. No. 15/977,553 filed May 11, 2018, issued as U.S. Pat. No. 10,340,022 on Jul. 2, 2019, which claims the benefit of U.S. patent application No. 62/506,641, filed on May 16, 2017, in the U.S. Intellectual Property Office, and Korean Patent Application No. 10-2017-0121313, filed on Sep. 20, 2017, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The inventive concept relates to a memory device, and more particularly, to a nonvolatile memory including an on-die-termination (hereinafter, referred to as “ODT”) circuit, a storage device including the nonvolatile memory, and a method of operating the storage device. 
     2. Discussion of Related Art 
     A storage device may include a nonvolatile memory and a controller configured to control the nonvolatile memory. Communication between the nonvolatile memory and the controller may be performed at a relatively lower operation frequency than communication performed in a memory system including a high speed memory, such as dynamic random-access memory (DRAM) or static random-access memory (SRAM). Accordingly, the quality of the signal (e.g., signal integrity) between the nonvolatile memory and the controller was not a critical factor for the overall performance of the storage device. However, recently, high speed operation of the storage device has been required, and thus, signal integrity has become a more important factor for the storage device in order to improve the overall performance of a computing system or a mobile communication system that includes the memory device. 
     SUMMARY 
     According to an exemplary embodiment of the inventive concept, a nonvolatile memory (NVM) device is provided. The NVM device includes a data pin, a control pin, an on-die termination (ODT) pin, and a plurality of NVM memory chips commonly connected to the data pin and the control pin. A first NVM chip among the NVM chips includes an ODT circuit. The first NVM chip determines one of an ODT write mode and an ODT read mode based on a control signal received through the control pin and an ODT signal received through the ODT pin, uses the ODT circuit to perform an ODT on the data pin during the ODT write mode, and uses the ODT circuit to perform the ODT on the control pin during the ODT read mode. 
     According to an exemplary embodiment of the inventive concept, a nonvolatile memory (NVM) device is provided. The NVM device includes a data pin, a control pin, a first on-die termination (ODT) pin, a second ODT pin, and a plurality of NVM memory chips commonly connected to the data pin and the control pin. A first NVM chip among the NVM chips includes an ODT circuit. The first NVM chip determines one of an ODT write mode and an ODT read mode based on a first ODT signal received through the first ODT pin and a second ODT signal received through the second ODT pin, uses the ODT circuit to perform an ODT on the data pin during the ODT write mode, and uses the ODT circuit to perform the ODT on the control pin during the ODT read mode. 
     According to an exemplary embodiment of the inventive concept, a nonvolatile memory (NVM) device is provided. The NVM device includes a data pin, a first control pin, a second control pin, and a plurality of NVM memory chips commonly connected to the data pin and the first control pin. The first NVM chip determines one of an ODT write mode and an ODT read mode based on a first control signal received through the first control pin and a second control signal received through the second control pin, uses the ODT circuit to perform an ODT on the data pin during the ODT write mode, uses the ODT circuit to perform the ODT on the first control pin during the ODT read mode when the first control signal is a read enable signal, and uses the ODT circuit to perform the ODT on a read enable pin of the NVM device during the ODT read mode when the first and second control signals indicate whether the ODT is to be performed on the data pin or the read enable pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is block diagram schematically showing a storage device according to an exemplary embodiment of the inventive concept; 
         FIG. 2  is a circuit diagram of an example of an on-die-termination (ODT) circuit of  FIG. 1 ; 
         FIG. 3  shows connection of ODT circuits during a write operation of the storage device of  FIG. 1  and  FIG. 4  shows connection of ODT circuits during a read operation of the storage device of  FIG. 1 ; 
         FIG. 5  is a block diagram showing in more detail the storage device of  FIG. 1 , according to an exemplary embodiment of the inventive concept; 
         FIG. 6  is a block diagram showing in detail a first memory chip according to an exemplary embodiment of the inventive concept; 
         FIG. 7A  is a timing view of a write operation according to an embodiment and  FIG. 7B  is a timing view of a read operation according to an embodiment; 
         FIG. 8  is a block diagram showing in detail an ODT control circuit of  FIG. 5  according to an exemplary embodiment of the inventive concept; 
         FIG. 9  is a block diagram showing in detail a first memory chip according to an exemplary embodiment of the inventive concept; 
         FIG. 10A  is a timing view of a write operation according to an embodiment and  FIG. 10B  is a timing view of a read operation according to an embodiment; 
         FIG. 11  is a block diagram showing in detail an ODT control circuit of  FIG. 9  according to an exemplary embodiment of the inventive concept; 
         FIG. 12  is a block diagram showing in detail an input buffer control circuit of  FIG. 9  according to an exemplary embodiment of the inventive concept; 
         FIG. 13  is a flowchart of a write operation between a nonvolatile memory and a controller, according to an embodiment, and  FIG. 14  is a flowchart of a read operation between a nonvolatile memory and a controller, according to an embodiment; 
         FIG. 15  is a block diagram schematically showing a storage device according to an exemplary embodiment of the inventive concept; 
         FIG. 16  shows connection of ODT circuits during a write operation of the storage device of  FIG. 15  and  FIG. 17  shows connection of ODT circuits during a read operation of the storage device of  FIG. 15 ; 
         FIG. 18  is a block diagram showing in detail a first memory chip according to an exemplary embodiment of the inventive concept; 
         FIG. 19A  is a timing view of a write operation according to an embodiment and  FIG. 19B  is a timing view of a read operation according to an embodiment; 
         FIG. 20  is a flowchart of a write operation between a nonvolatile memory and a controller, according to an embodiment, and  FIG. 21  is a flowchart of a read operation between a nonvolatile memory and a controller, according to an embodiment; and 
         FIG. 22  is a block diagram showing an electronic apparatus according to an exemplary embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a block diagram schematically showing a storage device SD 1  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 1 , the storage device SD 1  includes a nonvolatile memory (NVM)  10  and a controller  20  (e.g., a control circuit), and the NVM  10  includes a first NVM chip  100  and a second NVM chip  200 . The NVM  10  may include a plurality of NVM chips including at least the first and second NVM chips  100  and  200 , and thus, may be referred to as “a multi-chip memory.” For example, each of the first and second NVM chips  100  and  200  may be a dual die package (DDP) or a quadruple die package (QDP). Each NVM chip may include a plurality of memory blocks. 
     The first NVM chip  100  includes an on-die-termination (ODT) circuit  101 , and the second NVM chip  200  includes an ODT circuit  201 . According to an embodiment, each of the first and second NVM chips  100  and  200  is a NAND flash memory chip. However, the present inventive concept is not limited thereto. For example, at least one of the first and second NVM chips  100  and  200  may be a resistive memory chip, such as resistive random-access memory (ReRAM), phase change RAM (PRAM), and magnetic RAM (MRAM). Hereinafter, the first and second NVM chips  100  and  200  will be referred to as the first and second chips  100  and  200 , for convenience. 
     The NVM  10  and the controller  20  communicate with each other via first through fourth signal lines SL 1  through SL 4 . Commands and addresses may be transmitted via the first signal lines SL 1 , and data signals DQ may be transmitted via the first signal lines SL 1 . For example, the addresses indicate locations in the NVM  10 , the data signals DQ include data, and the commands may include a write command that indicates an address to write the data or a read command that indicates an address to receive the data from. The first signal lines SL 1  may be referred to as input and output lines or input and output buses. Hereinafter, descriptions will be given by focusing on operations of the ODT circuits  101  and  201  in a section in which the data signals DQ are transmitted via the first signal lines SL 1 . Here, the first signal lines SL 1  may be referred to as data lines or data buses. A data strobe signal (DQS) may be transmitted via the second signal line SL 2 , and the second signal line SL 2  may be referred to as a data strobe signal line or a data strobe signal bus. A control signal CTRL may be transmitted via the third signal line SL 3 , and the third signal line SL 3  may be referred to as a control signal line. An ODT signal (ODTx) may be transmitted via the fourth signal line SL 4 , and the fourth signal line SL 4  may be referred to as an ODT signal line. 
     During a write operation, the controller  20  outputs a write command and an address, and then outputs the data signals DQ and the data strobe signal DQS. During a read operation, the controller  20  outputs a read command and an address, and then receives the data signals DQ. In an embodiment, the data strobe signal DQS is toggled at a high speed first frequency. Thus, the data strobe signal DQS may be reflected from the first or the second memory chip  100  or  200 , which is non-selected. Examples of the high speed first frequency includes 400 MHz, 500 MHz, 600 MHz, etc. 
     The controller  20  generates the ODT signal ODTx to control the ODT circuits  101  and  201 , and the control signal CTRL to control operations of the first and second memory chips  100  and  200 . In an exemplary embodiment, the ODT signal ODTx controls when to enable (e.g., activate) or disable (e.g., deactivate) the ODT circuits  101  and  201 . According to an embodiment, the control signal CTRL includes a read enable signal nREx for enabling a read operation of the first and second memory chips  100  and  200 . In an embodiment, the read enable signal nREx is toggled at a high speed second frequency. Thus, the read enable signal nREx may be reflected from the first or the second memory chip  100  or  200 , which is non-selected. For example, the selected memory chip may be the memory chip that is read from or written to (e.g., processes a read or write command), whereas the non-selected memory chip may be the memory chip that is standing by (e.g., not currently processing a read or a write command). In an exemplary embodiment, the first frequency and the second frequency are the same. 
     According to an embodiment, during a section (e.g., time period) in which the data strobe signal DQS is toggled at the first frequency for a write operation, the controller  20  activates the ODT signal ODTx to prohibit the data strobe signal DQS from being reflected from the first or the second memory chip  100  or  200 , which is non-selected and in a stand-by state. According to an embodiment, during a section in which the read enable signal nREx is toggled at the second frequency for a read operation, the controller  20  activates the ODT signal ODTx to prohibit the read enable signal nREx from being reflected from the first or the second memory chip  100  or  200 , which is non-selected and in a stand-by state. 
     The NVM  10  includes first through fourth pins P 1  through P 4 , and the first and second memory chips  100  and  200  may be commonly connected to each of the first through fourth pins P 1  through P 4 . The first through fourth pins P 1  through P 4  may be referred to as first through fourth pads. The first pins P 1  are connected to the first signal lines SL 1 , respectively, and may be referred to as input and output pins or data pins. The second pin P 2  is connected to the second signal line SL 2 , and may be referred to as a data strobe signal pin. The third pin P 3  is connected to the third signal line SL 3 , and may be referred to as a control signal pin. The fourth pin P 4  is connected to the fourth signal line SL 4 , and may be referred to as an ODT pin. In an embodiment, the controller  20  is configured to output an ODT setting command to the NVM  10  indicating whether ODT is permissible (e.g., permissible on the data pin DQ, the data strobe pin DQS, the control pin CTRL, etc.), and the NVM  10  is configured to interpret/execute the ODT setting command. For example, upon receiving the ODT setting command, the NVM  10  could configure one or more of its pins to be an ODT pin that receives an ODT signal. Meanwhile, the controller  20  includes first through fourth pins P 1 ′ through P 4 ′ connected to the first through fourth signal lines SL 1  through SL 4 , respectively. 
     For example, the second signal line SL 2  may be commonly connected to the first and second memory chips  100  and  200  via the second pin P 2 , and the data strobe signal DQS transmitted via the second signal line SL 2  may be commonly applied to the first and second memory chips  100  and  200 . For example, when the first memory chip  100  is non-selected and the second memory chip  200  is selected, the data strobe signal DQS may be reflected from the first memory chip  100 , which is in a stand-by state. 
     However, according to the present embodiment, the NVM  10  receives the ODT signal ODTx from the controller  20  via the fourth pin P 4 . The non-selected first memory chip  100  enables the ODT circuit  101  based on the ODT signal ODTx, and the ODT circuit  101  becomes connected to the second signal line SL 2 . In an embodiment, connection of an ODT circuit to a signal line may attach a termination resistance to that signal line. Accordingly, the data strobe signal DQS may be prohibited from being reflected from the first memory chip  100  in the stand-by state, and thus, a signal integrity margin may be improved. 
     According to an exemplary embodiment, the NVM  10  receives the control signal CTRL from the memory controller  20  via the third pin P 3 . The first memory chip  100 , which is non-selected, determines whether an operation with respect to the second memory chip  200 , which is selected, is a write operation or a read operation, based on the control signal CTRL, and determines an ODT mode based on a result of the determination. For example, the control signal CTRL may be a read enable signal nREx. Hereinafter, descriptions will be given by focusing on embodiments in which the control signal CTRL is the read enable signal nREx. However, the present inventive concept is not limited thereto, and the control signal CTRL may be at least one of various control signals indicating operations of the NVM  10 . In an exemplary embodiment, the NVM  10  may modify an impedance of the ODT circuit  101  based on an impedance signal received through the first pin P 1 . 
     The ODT circuit  101  includes an ODT switch SW 1  and an ODT resistor R TT  connected in series. The ODT switch SW 1  is connected between a power voltage terminal V TT  and the ODT resistor R TT , and is driven based on the ODT signal ODTx and the control signal CTRL. A voltage provided to the power voltage terminal VTT may be the same as a power supply voltage supported the NVM  10 . An end of the ODT resistor R TT  is connected to the ODT switch SW 1  and the other end of the ODT resistor R TT  may be connected to one of the first through third signal lines SL 1  through SL 3 . When the ODT switch SW 1  is turned on (e.g., closed) in response to the ODT signal ODTx and the control signal CTRL, the power voltage terminal V TT  is connected to one of the first through third signal lines SL 1  through SL 3 . However, structures of the ODT circuit  101  are not limited thereto. For example, the ODT resistor R TT  may be arranged between the power voltage terminal V TT  and the ODT switch SW 1 . The ODT circuit  201  includes the ODT resistor R TT  and an ODT switch SW 2  connected in series and may be implemented substantially the same as the ODT circuit  101 . In an embodiment, an ODT switch (e.g., SW 1  or SW 2 ) is implemented by a transistor. 
     When the NVM  10  does not include the fourth pin P 4 , the controller  20  may transmit an ODT enable command to the first memory chip  100 , before transmitting a write command or a read command to the second memory chip  200 . However, in this case, command overhead is increased since the controller  20  spends more time inputting commands to the NVM  10 . In particular, when the NVM  10  includes three or more memory chips, the number of non-selected memory chips may be two or more. Here, since the ODT enable command has to be transmitted to each of the non-selected memory chips, the command overhead may further be increased. 
     However, according to the present embodiment shown in  FIG. 1 , the NVM  10  includes the fourth pin P 4 , and the first and second memory chips  100  and  200  are commonly connected to the fourth pin P 4  so as to receive the ODT signal ODTx. Thus, while the controller  20  transmits the write command or the read command with respect to the second memory chip  200  through the first signal lines SL 1 , the controller  20  may simultaneously transmit the ODT signal ODTx through the fourth signal line SL 4 . The ODT signal ODTx defines a time period (e.g., an enable section) during which the ODT circuit  101  included in the first memory chip  100  is to be activated when the first memory chip  100  is not selected and the second memory chip  200  is selected. Therefore, the command overhead may be decreased, and the performance of the storage device SD 1  may be improved. 
     In an exemplary embodiment, the storage device SD 1  is an internal memory mounted in an electronic apparatus. For example, the storage device SD 1  may be a solid state drive (SSD), an embedded universal flash storage (UFS) memory device, or an embedded multimedia card (eMMC). In an exemplary embodiment, the storage device SD 1  is an external memory detachable from the electronic apparatus. For example, the storage device SD 1  may include a UFS memory card, compact flash (CF), secure digital (SD), micro secure digital (Micro-SD), mini secure digital (Mini-SD), extreme digital (xD), or a memory stick. 
       FIG. 2  is a circuit diagram of an example  101 ′ of the ODT circuit  101  of  FIG. 1  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 2 , the ODT circuit  101 ′ includes p-type metal oxide semiconductor (PMOS) transistors PM 1  through PM 4 , n-type metal oxide semiconductor (NMOS) transistors NM 1  through NM 4 , and resistors R 11  through R 24 . The number of PMOS transistors, the number of NMOS transistors, and the number of resistors may vary according to embodiments. The PMOS transistors PM 1  through PM 4  may be turned on or turned off based on control signals PU 11  through PU 14  corresponding to the PMOS transistors PM 1  through PM 4 , and the NMOS transistors NM 1  through NM 4  may be turned on or turned off based on control signals PD 11  through PD 14  corresponding to the NMOS transistors NM 1  through NM 4 . For example, the control signals PU 11  through PU 14  and PD 11  through PD 14  may correspond to a first ODT control signal ODT EN 1  or a second ODT control signal ODT EN 2  of  FIG. 6 . 
     Accordingly, some of the resistors R 11  through R 24  may be connected to a pin Pn via a signal line SL, and a termination resistance of the ODT circuit  101 ′ may be determined For example, the termination resistance of the ODT circuit  101 ′ may be determined by the resistors that remain connected to the pin Pn. The pin Pn may be one of the first through third pins P 1  through P 3  of  FIG. 1  and may be adjusted to be the same as an impedance of the signal line SL corresponding to the termination resistance of the ODT circuit  101 ′. Accordingly, the ODT circuit  101 ′ may absorb energy of a signal transmitted via the signal line SL corresponding to the ODT circuit  101 ′, and may prohibit reflection of signals from a receiving terminal. 
       FIG. 3  shows connection of ODT circuits  101   a ,  101   b ,  101   c ,  201   a ,  201   b , and  201   c  during a write operation of the storage device SD 1  of  FIG. 1 , and  FIG. 4  shows connection of the ODT circuits  101   a ,  101   b ,  101   c ,  201   a ,  201   b , and  201   c  during a read operation of the storage device SD 1  of  FIG. 1 . 
     Referring to  FIGS. 3 and 4 , the first memory chip  100  includes the first ODT circuits  101   a  respectively connected to the first signal lines SL 1 , the second ODT circuit  101   b  connected to the second signal line SL 2 , and the third ODT circuit  101   c  connected to the third signal line SL 3 . The second memory chip  200  includes the first ODT circuits  201   a  respectively connected to the first signal lines SL 1 , the second ODT circuit  201   b  connected to the second signal line SL 2 , and the third ODT circuit  201   c  connected to the third signal line SL 3 . Here, the first through second ODT circuits  101   a  through  201   b  may be referred to as ODT circuits for writing, and the third ODT circuits  101   c  and  201   c  may be referred to as ODT circuits for reading. 
     The controller  20  generates a read enable signal nREx and the read enable signal nREx is transmitted to the NVM  10  via the third signal line SL 3 . The NVM  10  receives the read enable signal nREx via the third pin P 3 . For example, in order to enable a read operation with respect to one of the first and second memory chips  100  and  200 , the read enable signal nREx is activated (e.g., set to a first logic level different from a second logic level used to represent a deactivated state). For example, in order to enable a write operation with respect to one of the first and second memory chips  100  and  200 , the read enable signal nREx is inactivated (or deactivated). 
     Referring to  FIG. 3 , the second memory chip  200  is selected and the first memory chip  100  is non-selected for a write operation. For example, during the write operation, data will be written to the selected memory chip and not written to the non-selected memory chip. In an embodiment, the controller  20  generates chip enable signals with respect to the first and second memory chips  100  and  200 , the read enable signal nREx, and an ODT signal ODTx. For example, the chip enable signal with respect to the first memory chip  100  is inactivated, the chip enable signal with respect to the second memory chip  200  is activated since the second memory chips  200  is the subject of the write, the read enable signal nREx is inactivated to indicate a write is to occur, and the ODT signal ODTx is activated. 
     The non-selected first memory chip  100  determines an operation performed with respect to the second memory chip  200  is a write operation, based on the read enable signal nREx, and thus determines an ODT mode as a write ODT mode. The non-selected first memory chip  100  enables the first and second ODT circuits  101   a  and  101   b  and disables the third ODT circuit  101   c , based on the ODT signal ODTx and the read enable signal nREx. Accordingly, ODT switches SW la included in the first ODT circuits  101   a , respectively, are turned on, and the ODT resistors R TT  are connected to the first signal lines SL 1 , respectively, so as to prohibit the data signals DQ transmitted via the first signal lines SL 1 , respectively, from being reflected. Also, an ODT switch SW 1   b  included in the second ODT circuit  101   b  may be turned on and the ODT resistor R TT  may be connected to the second signal line SL 2  so as to prohibit the data strobe signal DQS transmitted via the second signal line SL 2  from being reflected. If the first memory chip  100  is instead the subject of the write (e.g., selected) and the second memory chip  200  is not selected, the selected second memory chip  200  enables the first and second ODT circuits  201   a  and  201   b  and disables the third ODT circuit  201   c  based on the ODT signal ODTx and the read enable signal nREx. 
     Referring to  FIG. 4 , the second memory chip  200  is selected and the first memory chip  100  is non-selected for a read operation. In an embodiment, the controller  20  generates chip enable signals with respect to the first and second memory chips  100  and  200 , the read enable signal nREx, and the ODT signal ODTx. For example, the chip enable signal with respect to the first memory chip  100  is inactivated, the chip enable signal with respect to the second memory chip  200  is activated, and both of the read enable signal nREx and the ODT signal ODTx are activated. 
     The non-selected first memory chip  100  determines an operation performed with respect to the second memory chip  200  is a read operation based on the read enable signal nREx, and thus determines an ODT mode is a read ODT mode. The non-selected first memory chip  100  disables the first and second ODT circuits  101   a  and  101   b  and enables the third ODT circuit  101   c  based on the ODT signal ODTx and the read enable signal nREx. Accordingly, an ODT switch SW 1   c  included in the third ODT circuit  101   c  is turned on (e.g., closed) and the ODT resistor R TT  is connected to the third signal line SL 3  so as to prohibit the read enable signal nREx transmitted via the third signal line SL 3  from being reflected. If the first memory chip  100  is instead the subject of the read (e.g., selected) and the second memory chip  200  is not selected, the selected second memory chip  200  disables the first and second ODT circuits  201   a  and  201   b  and enables the third ODT circuit  201   c  based on the ODT signal ODTx and the read enable signal nREx. 
       FIG. 5  is a block diagram showing in more detail the storage device SD 1  of  FIG. 1  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 5 , the first memory chip  100  includes an input and output (I/O) circuit  110  and an ODT control circuit  120 , and the input and output circuit  110  includes an ODT circuit  111 . The second memory chip  200  includes an input and output circuit  210  and an ODT control circuit  220 , and the input and output circuit  210  includes an ODT circuit  211 . Hereinafter, descriptions will be given by focusing on the first memory chip  100 , and the descriptions with respect to the first memory chip  100  may be applied to the second memory chip  200 . 
     The input and output circuit  110  may be connected to the first and second signal lines SL 1  and SL 2 , and include the ODT circuit  111 . The ODT control circuit  120  generates an ODT control signal ODT_EN to control the ODT circuit  111 , based on the ODT signal ODTx and the read enable signal nREx. According to an embodiment, when the ODT signal ODTx is activated, the ODT control circuit  120  detects a logic level of the read enable signal nREx and generates the ODT control signal ODT_EN based on the detected logic level. In an exemplary embodiment, when the ODT control signal ODT_EN is activated, the ODT circuit  111  is connected to the first and second signal lines SL 1  and SL 2 , and when the ODT control signal ODT_EN is inactivated, the ODT circuit  111  is disconnected from the first and second signal lines SL 1  and SL 2 . In an exemplary embodiment, when the ODT control signal ODT_EN is activated and the read enable signal nREx is inactivated, the ODT circuit  111  is connected to the first and second signal lines SL 1  and SL 2 , and when the ODT control signal ODT_EN is inactivated, the ODT circuit  111  is disconnected from the first and second signal line SL 1  and SL 2 . In an exemplary embodiment, when the ODT control signal ODT_EN is activated and the read enable signal nREx is activated, the ODT circuit  111  is connected to the third signal line SL 3 , and when the ODT control signal ODT_EN is inactivated, the ODT circuit  111  is disconnected from the third signal line SL 3 . 
       FIG. 6  is a block diagram showing in detail a first memory chip  100   a  according to an exemplary embodiment of the inventive concept. For example, the first memory chip  100   a  may correspond to an example of the first memory chip  100  of  FIG. 5 . However, structures of the first memory chip  100   a  are not limited to the structure of the first memory chip  100  of  FIG. 5 , and may be applied to the second memory chip  200 . 
     Referring to  FIG. 6 , the first memory chip  100   a  includes the input and output circuit  110 , the ODT control circuit  120 , and first and second input circuits  130  and  140 . Also, the first memory chip  100   a  may further include a memory core MC. The memory core MC may include a memory cell array, a row decoder, a page buffer, a voltage generator, etc., and may be referred to as a data path. The second memory chip  200  may be implemented substantially the same as the first memory chip  100   a.    
     The input and output circuit  110  include the ODT circuits  111  and an input and output buffer  112 . The input and output circuit  110  may transmit and receive a plurality of data signals DQ 0  through DQn via a plurality of first pins P 1 _ 0  through P 1 _n, and transmit and receive the data strobe signal DQS via the second pin P 2 . Here, n is a positive integer, for example, 7. The input and output buffer  112  may output data to the memory core MC or receive data from the memory core MC. For example, the ODT circuits  111  may include the first and second ODT circuits  101   a  and  101   b  of  FIGS. 3 and 4 . 
     The first input circuit  130  receives the read enable signal nREx via the third pin P 3 . The first input circuit  130  includes an ODT circuit  131  and an input buffer  132 . The input buffer  132  receives the read enable signal nREx, and outputs an internal read enable signal nREi by buffering the received read enable signal nREx. The ODT circuit  131  may include the third ODT circuit  101   c  of  FIGS. 3 and 4 . 
     The second input circuit  140  receives the ODT signal ODTx via the fourth pin P 4 , and outputs an internal ODT signal ODTi from the received ODT signal ODTx. For example, the second input circuit  140  may include an input buffer and the input buffer may output the internal ODT signal ODTi by buffering the ODT signal ODTx. 
     In an embodiment, the ODT control circuit  120  determines an ODT mode based on the internal ODT signal ODTi and the internal read enable signal nREi, and generates first and second ODT control signals ODT_EN 1  and ODT_EN 2  to control the ODT circuits  111  and  131 , respectively, based on the determined ODT mode. For example, when the determined ODT mode is a write ODT mode, the first ODT control signal ODT_EN 1  has an enable level (e.g., logic “high”). For example, when the determined ODT mode is a read ODT mode, the second ODT control signal ODT_EN 2  has an enable level (e.g., logic “high”). According to the present embodiment, the first memory chip  100   a  controls the ODT circuits  111  and  131  based on operations of the second input circuit  140 , the ODT control circuit  120  and the input buffer  132 , and thus, current consumption used for the ODT control operation may be reduced. 
       FIG. 7A  is a timing diagram of a write operation according to an embodiment and  FIG. 7B  is a timing diagram of a read operation according to an embodiment. 
     Referring to  FIGS. 6 and 7A , the read enable signal nREx is logic “high” (e.g., a write is occurring) and thus, the internal read enable signal nREi is logic “high”. The internal ODT signal ODTi is activated to an enable level, for example, a logic “high” in a preamble section PRE 1  of the data strobe signal DQS, and is inactivated to a disable level, for example, a logic “low” in a post-amble section POST 1  of the data strobe signal DQS. Here, the preamble section PRE 1  of the data strobe signal DQS is a logic “low” section before a toggling section of the data strobe signal DQS, and the post-amble section POST 1  of the data strobe signal DQS is a logic “low” section after the toggling section of the data strobe signal DQS. In an embodiment, the ODT signal ODTi is enabled within the preamble section PRE 1  while an address latch enable signal, a command latch enable signal, and the data strobe signal DQS are logic “low”. 
     The ODT control circuit  120  detects a logic level of the internal read enable signal nREi at the activation point of the internal ODT signal ODTi, that is, when a level of the internal ODT signal ODTi is enabled. For example, the activation point of the internal ODT signal ODTi may correspond to a rising edge of the internal ODT signal ODTi. However, the present inventive concept is not limited thereto. In an alternate embodiment, the activation point of the internal ODT signal ODTi corresponds to a falling edge of the internal ODT signal ODTi. In the alternate embodiment, the ODT control circuit  120  is designed to detect the logic level of the internal read enable signal nREi at the falling edge of the internal ODT signal ODTi. In an exemplary embodiment, when the detected logic level of the internal read enable signal nREi is “high,” the ODT control circuit  120  determines the ODT mode is the write ODT mode, and activates the first ODT control signal ODT_EN 1  based on the determined write ODT mode. Thus, the ODT circuits  111  included in the input and output circuit  110  are enabled. 
     Next, the ODT control circuit  120  inactivates the first ODT control signal ODT_EN 1  at the inactivation point of the internal ODT signal ODTi, that is, when a level of the internal ODT signal ODTi is disabled (e.g., at a falling edge). Accordingly, the ODT circuits  111  included in the input and output circuit  110  are disabled. According to an embodiment, the ODT control circuit  120  detects the logic level of the internal read enable signal nREi at the falling edge of the internal ODT signal ODTi, and when the detected logic level is “high”, determines that the write operation of the selected second memory chip  200  has completed and inactivates the first ODT control signal ODT_EN 1 . 
     Referring to  FIGS. 6 and 7B , the internal ODT signal ODTi is activated to a logic “high” in a preamble section PRE 2  of the read enable signal nREx, and inactivated to a logic “low” in a post-amble section POST 2  of the read enable signal nREx. Here, the preamble section PRE 2  of the read enable signal nREx is a logic “low” section before a toggling section of the read enable signal nREx and the post-amble section POST 2  of the read enable signal nREx is a logic “low” section after the toggling section of the read enable signal nREx. In an exemplary embodiment, the ODT signal ODTi is activated within the preamble section PRE 2  after the read enable signal nREx falls. The internal read enable signal nREi transitions to a logic “low” in the preamble section PRE 2  of the read enable signal nREx and maintains a logic “high” after the toggling section of the read enable signal nREx. 
     The ODT control circuit  120  detects a logic level of the internal read enable signal nREi at the activation point of the internal ODT signal ODTi, for example, at a rising edge of the internal ODT signal ODTi. In an exemplary embodiment, when the detected logic level of the internal read enable signal nREi is “low” the ODT control circuit  120  determines an ODT mode is a read ODT mode and activates the second ODT control signal ODT_EN 2  based on the determined read ODT mode. Accordingly, the ODT circuit  131  included in the first input circuit  130  is enabled. 
     Next, the ODT control circuit  120  inactivates the second ODT control signal ODT_EN 2  at an inactivation point of the internal ODT signal ODTi, for example, at a falling edge of the internal ODT signal ODTi. Accordingly, the ODT circuit  131  included in the first input circuit  130  is disabled. According to an embodiment, the ODT control circuit  120  detects a logic level of the internal read enable signal nREi at the falling edge of the internal ODT signal ODTi, and when the detected logic level is “low,” determines that the read operation of the selected second memory chip  200  has completed and inactivates the second ODT control signal ODT_EN 2 . 
       FIG. 8  is a block diagram showing in detail the ODT control circuit  120  of  FIG. 5  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 8 , the ODT control circuit  120  includes a delay unit  121  (e.g., a delay circuit), an inverter  122 , first and second flip-flops  123  and  124 . The delay unit  121  receives the internal ODT signal ODTi and delays the received internal ODT signal ODTi for a predetermined period of time to output a delayed internal ODT signal ODTi_d. The delayed internal ODT signal ODTi_d is applied to a clock terminal CLK of the first and second flip-flops  123  and  124 . 
     An output of the inverter  122 , that is, an inverted signal of the internal read enable signal nREi, is applied to an input terminal D of the first flip-flop  123 , and the second ODT control signal ODT_EN 2  is output from an output terminal Q of the first flip-flop  123 . The internal read enable signal nREi is applied to an input terminal D of the second flip-flop  124  and the first ODT control signal ODT_EN 1  is output from an output terminal Q of the second flip-flop  124 . 
     For example, as illustrated in  FIG. 7A , when the logic level of the internal read enable signal nREi is “high” at a point in which the delayed internal ODT signal ODTi_d is activated, the first ODT control signal ODT_EN 1  is activated. For example, at the point in which the delayed internal ODT signal ODTi_d is activated, when the logic level of the internal read enable signal nREi is “low” as illustrated in  FIG. 7B , the second ODT control signal ODT_EN 2  is activated. 
       FIG. 9  is a block diagram showing in detail a first memory chip  100   a ′ according to an exemplary embodiment of the inventive concept. For example, the first memory chip  100   a ′ may correspond to a modified example of the first memory chip  100   a  of  FIG. 6 . 
     Referring to  FIG. 9 , the first memory chip  100   a ′ includes the input and output circuit  110 , an ODT control circuit  120 ′, first and second input circuits  130 ′ and  140 , an input buffer control circuit  150 , and the memory core MC. The ODT control circuit  120 ′ determines an ODT mode based on the internal ODT signal ODTi and the internal read enable signal nREi, and generates the first and second ODT control signals ODT_EN 1  and ODT_EN 2  based on the determined ODT mode. Also, the ODT control circuit  120 ′ generates a third ODT control signal ODT_EN 3  based on the first and second ODT control signals ODT_EN 1  and ODT_EN 2 . For example, when the first or the second ODT control signal ODT_EN 1  or ODT_EN 2  is activated, the third ODT control signal ODT_EN 3  is activated. 
     When the internal ODT signal ODTi is activated, the ODT control circuit  120 ′ detects a logic level of the internal read enable signal nREi in order to determine the ODT mode. In an exemplary embodiment, when the internal ODT signal ODTi is activated, the input buffer control circuit  150  activates an input buffer control signal BUF_EN in order to enable an input buffer  132 ′. Here, the detected logic level of the internal read enable signal nREi may be latched. 
     Meanwhile, after the ODT control circuit  120 ′ determines the ODT mode and activates the first or second ODT control signal ODT_EN 1  or ODT_EN 2  based on the determined ODT mode, the ODT control circuit  120 ′ no longer needs to detect the logic level of the internal read enable signal nREi. Thus, when the first or second ODT control signal ODT_EN 1  or ODT_EN 2  is activated, the input buffer control circuit  150  may inactivate the input buffer control signal BUF_EN so as to disable the input buffer  132 ′. Accordingly, power consumption of the input buffer  132 ′ may be reduced. 
     In an exemplary embodiment, the input buffer control circuit  150  generates the input buffer control signal BUF_EN for controlling the input buffer  132 ′, based on a buffer on signal BUF_ON, the internal ODT signal ODTi, and the third ODT control signal ODT_EN 3 . According to an embodiment, when the buffer on signal BUF_ON is activated, the input buffer control circuit  150  activates the input buffer control signal BUF_EN, and the input buffer  132 ′ is enabled. For example, the buffer on signal BUF_ON may be generated by control logic based on control signals, such as a chip selection signal and a write mode signal. According to an embodiment, when the internal ODT signal ODTi is activated and the third ODT control signal ODT_EN 3  is inactivated, the input buffer control circuit  150  activates the input buffer control signal BUF_EN, and the input buffer  132 ′ is enabled. Meanwhile, when the internal ODT signal ODTi and the third ODT control signal ODT_EN 3  are activated, the input buffer control circuit  150  inactivates the input buffer control signal BUF_EN, and the input buffer  132 ′ may is disabled. In an exemplary embodiment, the ODT control circuit  120 ′ may activate the input buffer  132 ′ when the ODT signal ODTi is activated, and may inactivate the input buffer  132 ′ after a pre-defined delay. 
       FIG. 10A  is a timing view of a write operation according to an embodiment and  FIG. 10B  is a timing view of a read operation according to an embodiment. 
     Referring to  FIGS. 9 and 10A , the input buffer control circuit  150  activates the input buffer control signal BUF_EN for only a section of a short period after the internal ODT signal ODTi transitions to an enable level, for example, logic “high.” Accordingly, the input buffer  132 ′is enabled to output the internal read enable signal nREi, and the ODT control circuit  120 ′ detects a logic “high” level of the internal read enable signal nREi, so as to determine the ODT mode as the write ODT mode. After the ODT mode is determined, the input buffer control circuit  150  inactivates the input buffer control signal BUF_EN and the internal read enable signal nREi may be latched. 
     The ODT control circuit  120 ′ activates the first ODT control signal ODT_EN 1  based on the determined ODT mode, and the ODT circuits  111  are enabled based on the activated first ODT control signal ODT_EN 1 . Thus, the ODT circuits  111  are respectively connected to signal lines via which the plurality of data signals DQ 0  through DQn and the data strobe signal DQS are transmitted via the first through second pins P 1 _ 0 , . . . , P 1 _ n , P 2 . Next, when the internal ODT signal ODTi is inactivated, the ODT control circuit  120 ′ inactivates the first ODT control signal ODT_EN 1  to disable the ODT circuits  111 . 
     Referring to  FIGS. 9 and 10B , the input buffer control circuit  150  activates the input buffer control signal BUF_EN for only a section of a short period after the internal ODT signal ODTi transitions to an enable level, for example, a logic “high.” Accordingly, the input buffer  132 ′ is enabled to output the internal read enable signal nREi, and the ODT control circuit  120 ′ detects a logic “low” level of the internal read enable signal nREi so as to determine the ODT mode as the read ODT mode. After the ODT mode is determined, the input buffer control circuit  150  inactivates the input buffer control signal BUF_EN and the internal read enable signal nREi may be latched. 
     The ODT control circuit  120 ′ activates the second ODT control signal ODT_EN 2  based on the determined ODT mode, and the ODT circuits  131  are enabled based on the activated second ODT control signal ODT_EN 2 . Thus, the ODT circuits  131  are connected to a signal line, via which the read enable signal nREx is transmitted via the third pin P 3 . Next, when the internal ODT signal ODTi is inactivated, the ODT control circuit  120 ′ inactivates the second ODT control signal ODT_EN 2 , to disable the ODT circuit  131 . Here, the internal read enable signal nREi may be re-set. 
       FIG. 11  is a block diagram showing in detail the ODT control circuit  120 ′ of  FIG. 9  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 11 , the ODT control circuit  120 ′ includes the delay unit  121 , the inverter  122 , the first and second flip-flops  123  and  124 , and a logic gate  125 . Unlike the ODT control circuit  120  of  FIG. 8 , the ODT control circuit  120 ′ according to the present embodiment further includes the logic gate  125 , and the aspects described with reference to  FIG. 8  may be applied to the present embodiment. The logic gate  125  may perform a logic operation with respect to the first and second ODT control signals ODT_EN 1  and ODT_EN 2  to output the third ODT control signal ODT_EN 3 . For example, the logic gate  125  may be an OR gate performing an OR operation with respect to the first and second ODT control signals ODT_EN 1  and ODT_EN 2 . Accordingly, when one of the first and second ODT control signals ODT_EN 1  and ODT_EN 2  is activated, the third ODT control signal ODT_EN 3  is activated. When both the first and second ODT control signals ODT_EN 1  and ODT_EN 2  are inactivated, the third ODT control signal ODT_EN 3  is inactivated. 
       FIG. 12  is a block diagram showing in detail the input buffer control circuit  150  of  FIG. 9  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 12 , the input buffer control circuit  150  includes an inverter  151 , and first and second logic gates  152  and  153 . The inverter  151  inverts the third ODT control signal ODT_EN 3 . The first logic gate  152  (e.g., an AND gate) performs an AND operation with respect to the internal ODT signal ODTi and an output of the inverter  151 . The second logic gate  153  (e.g., an OR gate) performs an OR operation with respect to the buffer on signal BUF_ON and an output of the first logic gate  152  in order to generate the input buffer control signal BUF_EN. 
     For example, when the first memory chip  100   a ′ is the non-selected memory chip, the first memory chip  100   a ′ is in a stand-by state, and thus, the input buffer  132 ′ is disabled. Here, when the internal ODT signal ODTi is activated, the buffer on signal BUF_ON is activated, and thus, the input buffer control signal BUF_EN is activated. The input buffer  132 ′ is enabled based on the activated input buffer control signal BUF_EN. 
     For example, when the third ODT control signal ODT_EN 3  is activated, the output of the inverter  151  is logic “low” and the output of the first logic gate  152  is always logic “low.” Here, when the buffer on signal BUF_ON is a logic “low” the buffer control signal BUF_EN, which is the output of the second logic gate  153 , may be inactivated, in order to disable the input buffer  132 ′. Thus, currents applied to the input buffer  132 ′ may be reduced. 
     For example, when the third ODT control signal ODT_EN 3  is inactivated, the output of the inverter  151  is logic “high.” Here, when the internal ODT signal ODTi is logic “high” the output of the first logic gate  152  may be logic “high” and the buffer control signal BUF_EN, which is the output of the second logic gate  153 , may be activated, in order to enable the input buffer  132 ′. Meanwhile, when the internal ODT signal ODTi is logic “low,” the output of the first logic gate  152  may be logic “low” and when the buffer on signal BUF_ON is logic “low,” the buffer control signal BUF_EN, which is the output of the second logic gate  153 , may be inactivated, in order to disable the input buffer  132 ′. 
       FIG. 13  is a flowchart of a write operation between the NVM  10  and the controller  20 , according to an exemplary embodiment of the inventive concept. For example, the NVM  10  and the controller  20  may correspond to the NVM  10  and the controller  20  of  FIG. 3 . 
     In operation S 110 , the controller  20  generates a write command WCMD and an address ADDR. In operation S 120 , the controller  20  generates a read enable signal nREx and an ODT signal ODTx. According to an embodiment, operations S 110  and S 120  are substantially simultaneously performed. In operation S 130 , the controller  20  transmits the write command WCMD, the address ADDR, the read enable signal nREx, and the ODT signal ODTx to the NVM  10 . For example, the write command WCMD and the address ADDR may be transmitted to the NVM  10  from the controller  20  via the first signal lines SL 1 , and the read enable signal nREx and the ODT signal ODTx may be transmitted to the NVM  10  from the controller  20  via the third and fourth signal lines SL 3  and SL 4 , respectively. 
     In operation S 140 , the NVM  10  determines the ODT mode as a write ODT mode based on the read enable signal nREx and the ODT signal ODTx, and generates a write ODT control signal. For example, the first and second memory chips  100  and  200  included in the NVM  10  may determine the ODT mode as the write ODT mode based on the read enable signal nREx and the ODT signal ODTx, and may generate the write ODT control signal. In operation S 150 , the NVM  10  enables the write ODT circuits. For example, the first memory chip  100  included in the NVM  10  may enable the write ODT circuits  101   a  and  101   b  and the second memory chip  200  included in the NVM  10  may enable the write ODT circuits  201   a  and  201   b . In operation S 160 , the controller  20  transmits data for writing to the NVM  10 . For example, the data signals DQ and the data strobe signal DQS may be transmitted to the NVM  10  from the controller  20  via the first and second signal lines SL 1  and SL 2 , respectively. In an exemplary embodiment, operation S 150  is performed after operation S 160 . 
     In operation S 170 , the controller  20  inactivates the ODT signal ODTx and in operation S 180 , the controller  20  transmits the inactivated ODT signal ODTx to the NVM  10 . In operation S 190 , the NVM  10  disables the write ODT circuits based on the inactivated ODT signal ODTx. For example, the first memory chip  100  included in the non-volatile memory  10  may disable the write ODT circuits  101   a  and  101   b  based on the inactivated ODT signal ODTx, and the second memory chip  200  included in the NVM  10  may disable the write ODT circuits  201   a  and  201   b  based on the inactivated ODT signal ODTx. 
       FIG. 14  is a flowchart of a read operation between the NVM  10  and the controller  20 , according to an exemplary embodiment of the inventive concept. For example, the NVM  10  and the controller  20  may correspond to the NVM  10  and the controller  20  of  FIG. 4 . 
     In operation S 210 , the controller  20  generates a read command RCMD and an address ADDR. In operation S 220 , the controller  20  generates a read enable signal nREx and an ODT signal ODTx. According to an embodiment, operations S 210  and S 220  are substantially simultaneously performed. In operation S 230 , the controller  20  transmits the read command WCMD, the address ADDR, the read enable signal nREx, and the ODT signal ODTx to the NVM  10 . 
     In operation S 240 , the NVM  10  determines the ODT mode as a read ODT mode based on the read enable signal nREx and the ODT signal ODTx, and generates the read ODT control signal. For example, the first and second memory chips  100  and  200  included in the NVM  10  may determine the ODT mode as the read ODT mode based on the read enable signal nREx and the ODT signal ODTx, and may generate the read ODT control signal. In operation S 250 , the NVM  10  enables the read ODT circuit. For example, the first memory chip  100  included in the NVM  10  may enable the read ODT circuit  101   c  and the second memory chip  200  included in the NVM  10  may enable the read ODT circuit  201   c . In operation S 260 , the NVM  10  transmits the read data to the controller  20 . 
     In operation S 270 , the controller  20  inactivates the ODT signal ODTx, and in operation S 280 , the controller  20  transmits the inactivated ODT signal ODTx to the NVM  10 . In operation S 290 , the NVM  10  disables the read ODT circuit based on the inactivated ODT signal ODTx. For example, the first memory chip  100  included in the non-volatile memory  10  may disable the read ODT circuit  101   c  based on the inactivated ODT signal ODTx, and the second memory chip  200  included in the NVM  10  may disable the read ODT circuit  201   c  based on the inactivated ODT signal ODTx. 
       FIG. 15  is a block diagram schematically showing a storage device SD 2  according to an exemplary embodiment of the inventive concept. 
     Referring to  FIG. 15 , the storage device SD 2  includes an NVM  30  and a controller  40 , and the NVM  30  includes first and second memory chips  300  and  400 . The first memory chip  300  includes an ODT circuit  301  and the second memory chip  400  includes an ODT circuit  401 . The storage device SD 2  may correspond to a modified example of the storage device SD 1  of  FIG. 1 , and the aspects described in detail with reference to  FIGS. 1 through 14  may be applied to the present embodiment. Hereinafter, descriptions will be given by focusing on differences between the storage device SD 1  of  FIG. 1  and the storage device SD 2  according to the present embodiment. 
     The NVM  30  and the controller  40  communicate with each other via first through fifth signal lines SL 1  through SL 5 . Commands and addresses may be transmitted via the first signal lines SL 1 , and next, the data DQ may be transmitted via the first signal lines SL 1 . The data strobe signal DQS may be transmitted via the second signal line SL 2 . The control signal CTRL may be transmitted via the third signal line SL 3 . A first ODT signal ODT 1   x  may be transmitted via the fourth signal line SL 4  and a second ODT signal ODT 2   x  may be transmitted via the fifth signal line SL 5 . 
     The controller  40  generates the first and second ODT signals ODT 1   x  and ODT 2   x  to control the ODT circuits  301  and  401  and the control signal CTRL to control operations of the first and second memory chips  300  and  400 . According to an embodiment, the control signal CTRL includes a read enable signal for enabling a read operation of the first and second memory chips  300  and  400 . 
     The NVM  30  includes first through fifth pins P 1  through P 5 , and the first and second memory chips  300  and  400  may be commonly connected to each of the first through fifth pins P 1  through P 5 . The first pins P 1  are connected to the first signal lines SL 1 , respectively. The second through fifth pins P 2  through P 5  are connected to the second through fifth signal lines SL 2  through SL 5 , respectively. Meanwhile, the controller  40  includes first through fifth pins P 1 ′ through P 5 ′ connected to the first through fifth signal lines SL 1  through SL 5 , respectively. 
     According to the present embodiment, the NVM  30  receives the first and second ODT signals ODT 1   x  and ODT 2   x  from the controller  40  via the fourth and fifth pins P 4  and P 5 , respectively. For example, the first ODT signal ODT 1   x  is a signal configured to control write ODT circuits (for example,  301   a ,  301   b ,  401   a , and  401   b  of  FIG. 16 ) and defines an enable section of the write ODT circuits (e.g., defines when to enable or disable the write ODT circuits). For example, the second ODT signal ODT 2   x  is a signal configured to control read ODT circuits (for example,  301   c  and  401   c  of  FIG. 16 ) and defines an enable section of the read ODT circuits (e.g., defines when to enable or disable the read ODT circuits). Accordingly, the non-selected first memory chip  300  may enable the ODT circuit  301  based on the first and second ODT signals ODT 1   x  and ODT 2   x , so as to prohibit reflection of signals from the first memory chip  300  in a stand-by state. Thus, the signal integrity margin may be improved. 
       FIG. 16  shows connection of the ODT circuits  301   a ,  301   b ,  301   c ,  401   a ,  401   b , and  401   c  during a write operation of the storage device SD 2  of  FIG. 15 . 
     Referring to  FIG. 16 , the second memory chip  400  is selected and the first memory chip  300  is non-selected for the write operation. In an embodiment, the controller  40  generates chip enable signals with respect to the first and second memory chips  300  and  400 , the read enable signal nREx, and the first and second ODT signals ODT 1   x  and ODT 2   x . For example, the chip enable signal with respect to the first memory chip  300  is inactivated, the chip enable signal with respect to the second memory chip  400  is activated, the read enable signal nREx and the second ODT signal ODT 2   x  are inactivated, and the first ODT signal ODT 1   x  is activated. 
     The non-selected first memory chip  300  determines an operation performed with respect to the second memory chip  400  as a write operation, based on the activated first ODT signal ODT 1   x . The non-selected first memory chip  300  enables the first and second ODT circuits  301   a  and  301   b  based on the first ODT signal ODT 1   x , and disables the third ODT circuit  301   c . Accordingly, ODT switches SW 1   a  respectively included in the first ODT circuits  301   a  are turned on, and ODT resistors R TT  are respectively connected to the first signal lines SL 1  so as to prohibit reflection of the data signal DQ transmitted via the first signal lines SL 1 . Also, an ODT switch SW 1   b  included in the second ODT circuit  301   b  is turned on, and the ODT resistor R TT  is connected to the second signal line SL 2  so as to prohibit reflection of the data strobe signal DQS transmitted via the second signal line SL 2 . 
     Likewise, the selected second memory chip  400  enables the first and second ODT circuits  401   a  and  401   b  based on the first ODT signal ODT 1   x , and disables the third ODT circuit  401   c . However, the present inventive concept is not limited thereto. In some embodiments, the selected second memory chip  400  determines whether to enable the first and second ODT circuits  401   a  and  401   b  by further taking into account a chip selection signal, etc., and may disable the first and second ODT circuits  401   a  and  401   b.    
       FIG. 17  shows connection of the ODT circuits  301   a ,  301   b ,  301   c ,  401   a ,  401   b , and  401   c  during a read operation of the storage device SD 2  of  FIG. 15 . 
     Referring to  FIG. 17 , the second memory chip  400  is selected and the first memory chip  300  is non-selected for the read operation. In an embodiment, the controller  40  generates the chip enable signals with respect to the first and second memory chips  300  and  400 , the read enable signal nREx, and the first and second ODT signals ODT 1   x  and ODT 2   x . For example, the chip enable signal with respect to the first memory chip  300  is inactivated, the chip enable signal with respect to the second memory chip  400  is activated, the read enable signal nREx and the second ODT signal ODT 2   x  are activated, and the first ODT signal ODT 1   x  is inactivated. 
     The non-selected first memory chip  300  determines an operation performed with respect to the second memory chip  400  is a read operation based on the activated second ODT signal ODT 2   x . The non-selected first memory chip  300  disables the first and second ODT circuits  301   a  and  301   b  based on the second ODT signal ODT 2   x , and enables the third ODT circuit  301   c . Accordingly, an ODT switch SW 1   c  included in the third ODT circuit  301   c  is turned on, and the ODT resistor R TT  is connected to the third signal line SL 3  so as to prohibit reflection of the read enable signal nREx transmitted via the third signal line SL 3 . 
     Likewise, the selected second memory chip  400  disables the first and second ODT circuits  401   a  and  401   b  based on the second ODT signal ODT 2   x  and enables the third ODT circuit  401   c . However, the present inventive concept is not limited thereto. In an exemplary embodiment, the selected second memory chip  400  determines whether to enable the third ODT circuit  401   c  by further taking into account a chip selection signal, etc., and disables the third ODT circuit  401   c.    
       FIG. 18  is a block diagram showing in detail the first memory chip  300  according to an exemplary embodiment of the inventive concept. For example, the first memory chip  300  may correspond to the first memory chip  300  of  FIG. 15 . However, structures of the first memory chip  300  are not limited to the structure of the first memory chip  300  of  FIG. 15 , and may be applied to the second memory chip  400 . 
     Referring to  FIG. 18 , the first memory chip  300  includes an input and output circuit  310 , an ODT control circuit  320 , and first and second input circuits  330  and  340 . Also, the first memory chip  300  further includes the memory core MC. The memory core MC may include a memory cell array, a row decoder, a page buffer, a voltage generator, etc., and may be referred to as a data path circuit. The second memory chip  400  may be substantially similarly implemented as the first memory chip  300 . 
     The input and output circuit  310  include ODT circuits  311  and an input and output buffer  312 . The input and output circuit  310  transmits and receives the plurality of data signals DQ 0  through DQn via the plurality of first pins P 1 _ 0  through P 1 _ n , and transmits and receives the data strobe signal DQS via the second pin P 2 . Here, n is a positive integer, for example, 7. The input and output buffer  312  outputs data to the memory core MC or receives data from the memory core MC. For example, the ODT circuits  311  may include the first and second ODT circuits  301   a  and  301   b  of  FIGS. 16 and 17 . 
     The first input circuit  330  receives the read enable signal nREx via the third pin P 3 . The input circuit  330  includes an ODT circuit  331  and an input buffer  332 . The input buffer  332  receives the read enable signal nREx and buffers the received read enable signal nREx to output the internal read enable signal nREi. The ODT circuit  331  may include the third ODT circuit  301   c  of  FIGS. 16 and 17 . 
     The second input circuit  340  receives the first and second ODT signals ODT 1   x  and ODT 2   x  via the fourth and fifth pins P 4  and P 5 , respectively, and outputs first and second internal ODT signals ODT 1   i  and ODT 2   i  based on the received first and second ODT signals ODT 1   x  and ODT 2   x . For example, the second input circuit  340  may include input buffers and the input buffers may buffer the first and second ODT signals ODT 1   x  and ODT 2   x  to output the first and second internal ODT signals ODT 1   i  and ODT 2   i , respectively. 
     The ODT control circuit  320  determines an ODT mode based on the first and second internal ODT signals ODT 1   i  and ODT 2   i , and generates the first and second ODT control signals ODT_EN 1  and ODT_EN 2  to control the ODT circuits  311  and  321 , respectively, based on the determined ODT mode. For example, when the first internal ODT signal ODT 1   i  is activated, the ODT control circuit  320  determines the ODT mode is a write ODT mode and activates the first ODT control signal ODT_EN 1 . For example, when the second internal ODT signal ODT 2   i  is activated, the ODT control circuit  320  determines the ODT mode is a read ODT mode and activates the second ODT control signal ODT_EN 2 . 
       FIG. 19A  is a timing diagram of a write operation according to an embodiment and  FIG. 19B  is a timing diagram of a read operation according to an embodiment. 
     Referring to  FIGS. 18 and 19A , the read enable signal nREx is a logic “high” and thus, the internal read enable signal nREi is also a logic “high.” The first internal ODT signal ODT 1   i  is activated to an enable level, for example, a logic “high,” in the preamble section PRE 1  of the data strobe signal DQS, and is inactivated to a disable level, for example, a logic “low,” in the post-amble section POST 1  of the data strobe signal DQS. When the first internal ODT signal ODT 1   i  is activated, that is, at the activation point of the first internal ODT signal ODT 1   i  or when the first internal ODT signal ODT 1   i  is enabled, the ODT control circuit  320  determines the ODT mode as the write ODT mode, and activates the first ODT control signal ODT_EN 1  based on the determined write ODT mode. For example, the activation point of the first internal ODT signal ODT 1   i  may correspond to a rising edge of the first internal ODT signal ODT 1   i . However, the present inventive concept is not limited thereto. In some embodiments, the activation point of the first internal ODT signal ODT 1   i  corresponds to a falling edge of the first internal ODT signal ODT 1   i . For example, the ODT control circuit  320  may be designed to detect a logic level of the internal read enable signal nREi at the falling edge of the first internal ODT signal ODT 1   i.    
     Next, the ODT control circuit  320  inactivates the first ODT control signal OD_EN 1  at an inactivation point of the first internal ODT signal ODT 1   i , that is, when the first internal ODT signal ODT 1   i  is disabled (e.g., at the falling edge). According to an embodiment, the ODT control circuit  320  detects the logic level of the internal read enable signal nREi at the falling edge of the first internal ODT signal ODT 1   i , and when the detected logic level is “high,” the ODT control circuit  320  determines that the write operation of the second memory chip  400  has completed, and inactivates the first ODT control signal ODT_EN 1 . 
     Referring to  FIGS. 18 and 19B , the second internal ODT signal ODT 2   i  is activated to a logic “high” in the preamble section PRE 2  of the read enable signal nREx, and is inactivated to a logic “low” in the post-amble section POST 2  of the read enable signal nREx. The internal read enable signal nREi transitions to a logic “low” in the preamble section PRE 2  of the read enable signal nREx and maintains a logic “high” after a toggling section of the read enable signal nREx. The ODT control circuit  320  determines the ODT mode is a read ODT mode, at the activation point of the second internal ODT signal ODT 2   i , for example, at a rising edge of the second internal ODT signal ODT 2   i , and activates the second ODT control signal ODT_EN 2  based on the determined read ODT mode. 
     Next, the ODT control circuit  320  inactivates the second ODT control signal ODT_EN 2  at the inactivation point of the second internal ODT signal ODT 2   i , for example, at the falling edge of the second internal ODT signal ODT 2   i . According to an embodiment, the 
     ODT control circuit  320  detects a logic level of the internal read enable signal nREi at the falling edge of the second internal ODT signal ODT 2   i , and when the detected logic level is “low” determines that the read operation of the selected second memory chip  400  has completed and inactivates the second ODT control signal ODT_EN 2 . 
       FIG. 20  is a flowchart of a write operation between the NVM  30  and the controller  40 , according to an exemplary embodiment of the inventive concept. For example, the NVM  30  and the controller  40  may correspond to the NVM  30  and the controller  40  of  FIG. 16 . 
     In operation S 310 , the controller  40  generates a write command WCMD and an address ADDR. In operation S 320 , the controller  40  activates the first ODT signal ODT 1   x . According to an embodiment, operations S 310  and S 320  are substantially simultaneously performed. In operation S 330 , the controller  40  transmits the write command WCMD, the address ADDR, and the first ODT signal ODT 1   x  to the NVM  30 . For example, the write command WCMD and the address ADDR may be transmitted to the NVM  30  from the controller  40  via the first signal lines SL 1 , and the first ODT signal ODTx may be transmitted to the NVM  30  from the controller  40  via the fourth signal line SL 4 . 
     In operation S 340 , the NVM  30  determines an ODT mode is a write ODT mode based on the first ODT signal ODT 1   x  and generates a write ODT control signal. For example, the first and second memory chips  300  and  400  included in the NVM  30  may determine the ODT mode is the write ODT mode based on the first ODT signal ODT 1   x  and generate the write ODT control signal. In operation S 350 , the NVM  30  enables the write ODT circuits. For example, the first memory chip  300  included in the NVM  30  may enable the write ODT circuits  301   a  and  301   b  and the second memory chip  400  included in the NVM  30  may enable the write ODT circuits  401   a  and  401   b . In operation S 360 , the controller  40  transmits data for writing to the NVM  30 . For example, the data signals DQ and the data strobe signal DQS may be transmitted to the NVM  30  from the controller  40  via the first and second signal lines SL 1  and SL 2 , respectively. In some embodiments, operation S 350  is performed after operation S 360 . 
     In operation S 370 , the controller  40  inactivates the first ODT signal ODT 1   x , and in operation S 380 , the controller  40  transmits the inactivated first ODT signal ODT 1   x  to the NVM  30 . In operation S 390 , the NVM  30  disables the write ODT circuits based on the inactivated first ODT signal ODT 1   x . For example, the first memory chip  300  included in the NVM  30  may disable the write ODT circuits  301   a  and  301   b  based on the inactivated first ODT signal ODT 1   x , and the second memory chip  400  included in the NVM  30  may disable the write ODT circuits  401   a  and  401   b  based on the inactivated first ODT signal ODT 1   x.    
       FIG. 21  is a flowchart of a read operation between the NVM  30  and the controller  40 , according to an exemplary embodiment of the inventive concept. For example, the NVM  30  and the controller  40  may correspond to the NVM  30  and the controller  40  of  FIG. 17 . 
     In operation S 410 , the controller  40  generates a read command RCMD and an address ADDR. In operation S 420 , the controller  40  activates the second ODT signal ODT 2   x . According to an embodiment, operations S 410  and S 420  are substantially simultaneously performed. In operation S 430 , the controller  40  transmits the read command RCMD, the address ADDR, and the second ODT signal ODT 2   x  to the NVM  30 . 
     In operation S 440 , the NVM  30  determines an ODT mode is a read ODT mode based on the activated second ODT signal ODT 2   x , and generates a read ODT control signal. For example, the first and second memory chips  300  and  400  included in the NVM  30  may determine the ODT mode as the read ODT mode based on the second ODT signal ODT 2   x  and generate the read ODT control signal. In operation S 450 , the NVM  30  enables the read ODT circuit. For example, the first memory chip  300  included in the NVM  30  may enable the read ODT circuit  301   c  and the second memory chip  400  included in the NVM  30  may enable the read ODT circuit  401   c . In operation S 450 , the NVM  30  transmits the read data to the controller  40 . 
     In operation S 470 , the controller  40  inactivates the second ODT signal ODT 2   x , and in operation S 480 , the controller  40  transmits the inactivated second ODT signal ODT 2   x  to the NVM  30 . In operation S 490 , the NVM  30  disables the read ODT circuit based on the inactivated second ODT signal ODT 2   x . For example, the first memory chip  300  included in the NVM  30  may disable the read ODT circuit  301   c  based on the inactivated second ODT signal ODT 2   x  and the second memory chip  400  included in the NVM  30  may disable the read ODT circuit  401   c  based on the inactivated second ODT signal ODT 2   x.    
       FIG. 22  is a block diagram of an electronic apparatus  1000  according to an exemplary embodiment of the inventive concept. Referring to  FIG. 22 , the electronic apparatus  1000  includes a processor  1100 , a memory device  1200 , a storage device  1300 , a modem  1400 , an input and output device  1500 , and a power supply  1600 . According to the present embodiment, the storage device  1300  may be implemented according to the embodiments described in detail with reference to  FIGS. 1 through 21 . In detail, the storage device  1300  may include a NVM and a controller, and the NVM may include an ODT pin for receiving an ODT signal from the controller. Thus, when high speed communication is performed between the NVM and the controller in the storage device  1300 , reflection of signals may be prohibited and command overhead may be reduced, so as to improve the performance of the storage device  1300  and the overall performance of the electronic apparatus  1000 . 
     While the inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various modifications and equivalent other embodiments can be derived from the inventive concept.