# Patent

## Title
Apparatus and method for using a page buffer of a memory device as a temporary cache

## Abstract

An apparatus and method are provided for using a page buffer of a memory device as a temporary cache for data. A memory controller writes data to the page buffer and later reads out the data without programming the data into the memory cells of the memory device. This allows the memory controller to use the page buffer as temporary cache so that the data does not have to occupy space within the memory controller's local data storage elements. Therefore, the memory controller can use the space in its own storage elements for other operations.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 12/029,634 filed Feb. 12, 2008, now U.S. Pat. No. 8,046,527, that claims the benefit of prior U.S. Provisional Patent Application No. 60/891,115 filed Feb. 22, 2007, the disclosures of which are hereby incorporated by reference in their entirety.


TECHNICAL FIELD
The present invention relates generally to systems including memories. More particularly, the present invention relates to an apparatus and a method for using a memory as a temporary cache.
BACKGROUND
Electronic equipment uses memory devices, such as, for example, flash memories, for storing data or information. A flash system including a flash controller and a plurality of flash memory devices in a multi-drop configuration is disclosed in U.S. Patent Application Publication No. 2006/0198202 A1 (Erez). The flash controller sends data to the memory devices and controls operations multiple memory devices. The flash controller employs a memory resource such as static random access memory (SRAM) therein for storing code and/data to execute operations in its central processing unit (CPU).
The memory controller typically has its own data storage, which is used for caching of data for various applications. Increasing the capacity of the data storage elements might be beneficial for some applications due to the increased caching capability by the memory controller. However, increasing the capacity of the data storage results in increased cost.
SUMMARY
In accordance with an aspect of the present invention, there is provided a method for communicating with a plurality of memory devices connected in-series, at least one of the memory devices having a temporary store element, the method comprising: selecting a memory device of the plurality of memory devices, writing data stored in a data storage to the temporary store element of the selected memory device; and at a later time, reading the data from the temporary store element of the selected memory device.
The method may further comprise storing the read data back to the data storage. In the data storage, the space storing the data may be freed up after performing the step of writing.
Advantageously, the step of writing comprises: transmitting a write command including the data addressed to the selected memory device. The selected device writes the data to the temporary store element thereof in response to the write command.
The step of reading may comprise: transmitting a read command addressed to the selected memory device, the selected memory device reading the data from the temporary store element thereof in response to the read command; and receiving the read data through the last memory device of plurality of memory devices.
The method may further comprise selecting another memory device of the plurality of memory devices. The data may be written to the temporary store element of the another selected memory device. Later, the data may comprise a plurality of data parts including first and second data parts. The data parts may be temporarily stored separately and read back separately.
In accordance with another aspect of the present invention, there is provided an apparatus in communication with a plurality of memory devices connected in-series, each of the memory devices having a temporary store element, the apparatus comprising a processor for selecting a memory device of the plurality of memory devices, writing data in the temporary store element of the selected memory device; and reading back the data at a later time from the temporary store element of the selected memory device.
In accordance with a further aspect of the present invention, there is provided a system comprising: a plurality of memory devices connected in-series, each of the memory devices having a temporary store element and memory cells; and an apparatus for communicating with the plurality of memory devices. The apparatus comprises a processor for selecting a memory device of the plurality of memory devices, writing data in the temporary store element of the selected memory device; and reading back the data at a later time from the temporary store element of the selected memory device.
In accordance with an embodiment of the present invention, there is provided an apparatus for using a page buffer of a flash memory device as a temporary cache for data. A memory controller writes data to the page buffer and later reads out the data without programming the data into the memory cells of the flash memory device. This allows the memory controller to use the page buffer as temporary cache so that the data does not have to occupy space within the memory controller's local data storage. Therefore, the memory controller can free up space in its own storage to use the space for other operations or overwrite the occupied space with data for other operations.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.



BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described with reference to the attached drawings in which:
FIG. 1 is a block diagram of a system including a memory controller and a plurality of series-connected memory devices according to an embodiment of the present invention;
FIG. 2 is a block diagram of one of the memory devices shown in FIG. 1;
FIG. 3A is a block diagram of the system shown in FIG. 1 wherein a data transfer is performed for a temporary cache;
FIG. 3B is an illustration of the data transfer shown in FIG. 3A;
FIG. 4 is an example timing diagram for the data transfer in the system shown in FIG. 3A;
FIG. 5 is a block diagram of the system of FIG. 3A wherein memory devices are accessible after the data transfer;
FIG. 6 is a block diagram of the system of FIG. 3A wherein a data recovery from a temporary cache is performed;
FIG. 7 is an example timing diagram for the data recovery from the temporary cache in the system shown in FIG. 6;
FIG. 8 is a flowchart of an example method for using a page buffer as a temporary cache in the system of FIG. 3A;
FIG. 9A is a block diagram of the system of FIG. 3A wherein two data transfers are performed for a temporary cache;
FIG. 9B is an illustration of the data transfers shown in FIG. 9A;
FIG. 10 is an example timing diagram for the data transfers in the system shown in FIG. 9A;
FIG. 11 is a flowchart of an example method for using more than one page buffer of memory device as temporary caches in the system of FIG. 3A;
FIG. 12A is a block diagram of the system of FIG. 3A wherein three data transfers are performed for a temporary cache;
FIG. 12B is an illustration of the data transfers shown in FIG. 12A;
FIG. 12C is an example timing diagram for the data transfers in the system shown in FIG. 12A;
FIG. 13 is a table of an example command set;
FIG. 14 is a table of an example operation table;
FIG. 15 is a table showing an example of a detailed command and address format;
FIG. 16 is an example timing diagram showing basic input timing of a system;
FIG. 17 is an example timing diagram showing an input sequence of bit streams in a modular command NAND flash memory system;
FIG. 18 is an example timing diagram showing basic output timing in a memory system;
FIG. 19 is an example timing diagram showing an output sequence of bit streams in a memory system;
FIG. 20 is a flowchart of a method of page read operation; and
FIG. 21 is an example timing diagram showing page read and burst data read operations.



DETAILED DESCRIPTION
In the following detailed description of sample embodiments of the invention, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific sample embodiments in which the present invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical, and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
FIG. 1 shows a system according to an embodiment of the present invention. Referring to FIG. 1, the system includes a memory controller 110 and a serial interconnection of a plurality (M) of memory devices 120-1, 120-2, 120-3, . . . , and 120-M that are connected in-series, M being an integer greater than one. The memory controller 110 and the memory devices are interconnected via links having data width n, where n is an integer greater than or equal to one. In a case of n being one, the interconnection link will be a serial link and in a case of n being more than one, the interconnection link will be a parallel link. The memory controller 110 is connected to the first memory device 120-1 of the serial interconnection. The last memory device 120-M is also connected to the memory controller 110 so that first, second, third, . . . , and M-th memory devices 120-1, 120-2, 120-3, . . . , and 120-M of the serial interconnection together with the memory controller 110 form a ring connection structure. In the illustrated example, the memory devices 120-1-120-M are flash memory devices. Subsequent examples are also specific to flash memory. However, it is to be understood that embodiments of the present invention are also applicable to other types of non-volatile memory devices.
In the particular example shown in FIG. 1, each of the series-connected memory devices 120-1-120-M is a flash memory device, such as, for example, a NAND flash device. The flash memory device has a page buffer for temporary storing information on data. The stored information is written into flash memory cells of the device in accordance with page programming. Once programmed, the information stored in the page buffer is corrupted due to the verification process of the programmed cells.
The memory controller 110 has a data storage 112 and a processor 114. The data storage 112 stores various data that includes information on operation instructions, addresses and memory data to be processed and to be stored in the series-connected memory devices. The information on operation instructions is used for controlling the series-connected memory devices. The data storage 112 is, for example, a static random access memory (SRAM) or any type of embedded memory. More generally, any appropriate data storage may be implemented. The processor 114 performs operations of data processing and controlling of the memory devices accessing the data stored in the data storage 112.
In operation, the memory controller 110 sends a command input (CI) signal SC1 to the first device 120-1 and receives a command output (CO) signal SC(M+1) from the last device 120-M of the serial interconnection. Also, the memory controller 110 provides a command strobe input (CSI) signal SCS1 and a data strobe input (DSI) signal SDS1 to the first device 120-1 and provides a clock signal CK to all of the devices 120-1-120-M in a common clock source fashion.
The memory controller 110 has a plurality of connections: a command signal output connection CIO for sending the CI signal SC1; a command signal input connection COI for receiving the CO signal SC(M+1); an input strobe connection CSIO for sending the CSI signal SCS1; an output strobe connection DSIO for sending the DSI signal SDS1; and a clock output connection CKO for providing the clock signal CK.
The memory devices 120-1, 120-2, 120-3, . . . , and 120-M have page buffers 122-1, 122-2, 122-3, . . . , and 122-M, respectively, and flash memory cells 124-1, 124-2, 124-3, . . . , and 124-M, respectively. Each of the memory devices 120-1-120-M has a signal input connection CI for receiving the CI signal SCi (i=1 to M) from a previous device; a signal output connection CO for providing the CI signal SC(i+1) to a succeeding device; an input strobe input connection CSI for receiving the CSI signal SCSi from a previous device; an input strobe output connection CSO for sending an output CSI signal SCS(i+1) to the succeeding device; an output strobe input connection DSI for receiving the DSI signal SDSi from the previous device; and an output strobe output connection DSO for sending an output DSI signal SDS(i+1) to the succeeding device.
Each of the memory devices 120-1-120-M has a unique device address (DA) that is hard wired or pre-assigned, so that one device can be selected or designated at a time in normal operation. Example details of an architecture featuring devices connected in-series are provided in U.S. patent application Ser. No. 11/594,564 entitled “Daisy Chain Cascading Devices” filed Jul. 31, 2006, the disclosure of which is hereby incorporated by reference in its entirety. Other example details of an architecture feature devices connected in-series are provided in U.S. Provisional Patent Application Ser. No. 60/868,773 entitled “System and Method of Operating Memory Devices of Varying Type” filed Dec. 6, 2006, the disclosure of which is hereby incorporated by reference in its entirety. Examples of the device address assignment in a plurality of memory devices that are connected in-series are provided in U.S. Provisional Patent Application No. 60/787,710, filed Mar. 28, 2006; U.S. patent application Ser. No. 11/521,734 filed Sep. 15, 2006; U.S. Provisional Patent Application No. 60/802,645, filed May 23, 2006; and U.S. patent application Ser. No. 11/750,649 filed May 18, 2007, the disclosures of which are incorporated by reference in their entirety.
In the normal operation, the memory controller 110 sends the CI signal SC1 containing commands. A command includes a device address (DA) and an operation code (hereinafter OP code) representing an operation instruction. Some commands additionally include address information, and some commands additionally include data. Each OP code is associated with a respective operation. Each command is also referred to herein as having a type that is associated with the OP code contained in the command. For example, a command containing a read OP code is referred to as a “read command”. Each of the memory devices 120-1-120-M receives commands via its respective CI either directly from the memory controller in the case that a given device is the memory device connected directly to the memory controller (device 120-1 in the illustrated example), or from an adjacent preceding memory device for other devices. Each of the memory devices 120-1-120-M uses its respective CO for forwarding on commands either to the memory controller 110 in the case that a given device is the one having its output connected to the memory controller (device 120-M in the illustrated example), or to an adjacent following device. A command containing a write OP code addressed to a particular flash memory device results in data being written to a page buffer of that device, and then transferred from the page buffer to the flash memory cells of the memory device. A command containing a read OP code addressed to a particular flash memory device results in data being read from the flash memory cells of the memory device to the page buffer of the memory device and then being transferred out of the page buffer.
The memory controller 110 uses the page buffer of a memory device as a temporary cache for data. For example, the memory controller 110 uses the page buffer of a selected memory device as a temporary cache for data when the selected memory device is not presently being used for page programming or page read operations. Note that the selected memory device can be any one of the memory devices 120-1-120-M and is selected by the memory controller 110. Since the data is stored in the page buffer of the selected memory device, the memory controller 110 does not need to locally store the data in the data storage 112 of the memory controller 110. This allows the memory controller 110 to free up space in its data storage 112 that can otherwise be used for storing the data. The memory controller 110 can later read back the data from the page buffer of the selected memory device (the temporary cache) without programming the data into the memory cells of the selected memory device. In this manner, the page buffer of the selected memory device is accessed independently of the program operation. Note that the data may be in respect of any appropriate application in which there is data to be maintained.
In order for the page buffers to operate as temporary caches, three “modular” memory access commands are used. The first is referred to as a “burst data load” command and contains a burst data load OP code. This causes data to be written to the page buffer of a memory device, but this command alone does not cause the data to be transferred to the flash memory cells of the memory device. In the examples that follow, 4×h and 5×h are used for this purpose, but more generally the command structure would be defined on an implementation specific basis. The second is referred to as a “burst data read” command and contains a burst data read OP code. This causes data to be read directly from the page buffer without first reading from the flash memory cells. In the examples that follow, 2×h is used for this, but more generally, the command structure would be defined on an implementation specific basis. The third is referred to as a “page program” command and contains a page program OP code. This causes data that was previously stored in the page buffer to be written to the flash memory cells, destroying the contents of the page buffer in the process for verification purposes. In the examples that follow, 6×h is used for this, but more generally, the command structure would be defined on an implementation specific basis.
In the embodiments, a flexible modular command structure is used. An example command format is detailed











TABLE I





DA
OP Code
RA
CA
DATA







1 byte
1 byte
3 bytes
2 bytes
1-2112 bytes









In Table I, DA is a device address; OP code is an operation code; RA is a row address; CA is a column address; and DATA is write data. Examples of commands associated with OP codes are a “burst data load” command and a “burst data read” command. There are cases of: (i) either of row address or column address; (ii) neither row address nor column address; (iii) no data.
A particular example of the above-referenced command structure is provided in commonly assigned and co-pending U.S. patent application Ser. No. 11/840,692 filed Aug. 17, 2007 and U.S. Provisional Patent Application No. 60/892,705 filed Mar. 2, 2007, the contents of which are hereby incorporated by reference in their entirety. The applications disclose different command structures to distinguish core access operations that involve relatively long processing times from page buffer access operations that involve relatively short access times. Further details of the modular command structure will be later described with reference to FIGS. 13 to 21.
FIG. 2 shows one of the series-connected memory devices shown in FIG. 1. Referring to FIG. 2, a present memory device 120-i having a page buffer 122-i that can be used as a temporary cache for page read or other operations using a cache function. The memory device 120-i could be any one of the series-connected memory devices. The memory device 120-i includes the page buffer 122-i, the flash memory cells 124-i and a device controller 126-i. The page buffer 122-i is available for use both as a temporary cache and for the normal function of programming to the flash memory cells 124-i. The device controller 126-i includes any appropriate circuitry for facilitating processing of commands. It is to be understood that the device controller 126-i would include circuitry for processing commands.
In the normal operation, the memory controller 110 can transmit data to the page buffer 122-i without restriction to page programming. Data is written to the page buffer 122-i by the burst data load command as indicated at 133, and at a later time read by the burst data read command as indicated at 134. Note that when a temporary cache operation is performed, page programming is not performed. Therefore, the page buffer 122-i can be accessed relatively quickly. In this manner, the page buffer 122-i can be used as a temporary cache for data and/or instruction.
The device controller 126-i performs a device address match determination and data process. Thus, in the “write” operation, the device controller 126-i determines a device address match and loads the data of the input command to the page buffer 122-i in a case of the device addresses match. If the device addresses do not match, the device controller 126-i forwards the input command to the next memory device 120-(i+1). Also, in the “read back” operation, the device controller 126-i determines a device address match, the data is read from the page buffer 122-i and the read data is transferred to the next memory device 120-(i+1). If no device address match, the device controller 126-i forwards the input command to the next memory device 120-(i+1). The read data is propagated through the rest of the memory devices connected in-series and back to the memory controller 110.
A specific example of the temporary cache function of the page buffer for an architecture with series-connected devices will now be described with reference to FIG. 3A. FIG. 3A shows the system of FIG. 1 with emphasis of temporary cache for data. FIG. 3B illustrates the data transfer shown in FIG. 3A;
Referring to FIGS. 3A and 3B, the memory controller 110 and the memory devices 120-1, 120-2, 120-3, . . . , and 120-15 are connected in a ring structure. The signal issued by the memory controller 110 is propagated through the series-connected devises and the propagated signal is fed from the last device to the memory controller 110. In the particular example shown in FIG. 3A, the number M of the memory devices that are addressed with such a four bit numbering scheme is 15 (=24−1). Alternatively, the system can include any number of memory devices connected in-series and appropriate DAs are assigned accordingly. Referring to FIG. 3A, the device addresses DAs of the memory devices 120-1, 120-2, 120-3, . . . , and 120-15 are ‘0000’, ‘0001’, ‘0010’, . . . , and ‘1110’, respectively. The DAs are a with four bit binary numbers or values.
Each of the memory devices includes a device address match determiner (DAMD) for determining whether the device address DA contained in the input command matches the device address assigned to that device. The assigned address to each device is held in a register (not shown) thereof. In FIG. 3A and succeeding figures, the device address match determiners are shown instead of the device controllers in the respective memory devices. The device address match determiner is part of circuitry that forms the device controller of each memory device shown in FIG. 2. As shown in FIG. 3A, the memory devices 120-1, 120-2, 120-3, . . . , and 120-M have device address match determiners 128-1, 128-2, 128-3, . . . , and 128-15, respectively.
An example of data transfer signals used in the system of FIG. 3A to achieve a temporary cache function is shown in FIG. 4. In the system shown in FIG. 3A, it is assumed that the page buffer 122-3 of memory device 120-3 is available for use as a temporary cache.
FIG. 4 shows an example timing diagram for the data transfer in the system shown in FIG. 3A. Referring to FIGS. 3A and 4, each command sent from the data storage elements of the memory controller 110 is addressed to (or designated) specific memory device using the device address DA. In this particular example, the third memory device 120-3 is designated and selected. The memory controller 110 transmits a command that is a burst data load command containing the DA (‘0010’) of the third memory device 120-3 together with address information and data. This is transmitted along the devices connected in-series and each device will recognize a command if it is addressed to itself. Each of the first and second memory devices 120-1 and 120-2 is not selected. The command is processed by the third memory device 120-3 and the data in the command is stored in page buffer 122-3 of the memory device 120-3. In this example, the data transmission is via a ‘Burst Data Load’ OP code. Without additional command assertion, after the two ‘Burst Data Load’ commands, the page buffer 122-3 holds the data. After transmitting the data to the designated device 120-3, the flash memory controller 110 can switch the contents of the data storage 112 in order to start new operations, such as another page program or a page read.
In performing the transfer to the page buffer of a memory device, a command strobe input (CSI) signal SCS1 and a command input (CI) signal SC1 are provided by the memory controller 110. The CSI signal and the CI signal are propagated through the series-connected devices. The propagated CSI signal and CI signal are shown as SCSi and SCi, respectively.
To write to the page buffer 122-3 of the third memory device 120-3, the CI signal SCi contains the third device's DA (0010), operation instruction (“Burst Data Load”) represented by OP code, column address CA and data to be written. When the CSI signal SCS3 is asserted to enable the input (i.e., the CI signal SC3) to the third memory device 120-3, the device address match determiner 128-3 determines the device address match. Thus, the third device 120-3 is a designated device to be selected. Note that the data transfer to the third designated memory device 120-3 involves a third ‘Burst Data Load’ OP code addressed to the third designated memory device 120-3, which has an address of “0010” in this example. In the particular example, during the CSI signal being asserted for the third device, the data is transferred from the data storage 112 of the memory controller 110 to the page buffer 122-3 of the designated device 120-3 as indicated by 232 in FIG. 3A.
A similar transfer is performed for another designated memory device. In another implementation, a single command is issued for writing the same data to more than one memory device. Multiple or all device selection is possible by proper device designation by command or other means. In such example, during the CSI signal SCSi being asserted for the other device, the data is transferred from the data storage 112 of the memory controller 110 to the page buffer of the designated device.
FIG. 5 shows the system of FIG. 3A with accessible devices after the data transfer. In the illustrated example, it is assumed that the page buffer 122-3 of the designated memory device 120-3 is being used as a temporary cache for data and is therefore inaccessible. The other memory devices 120-1, 120-2 and 120-4-120-15 are considered accessible devices because there is no data stored in page buffers 122-1, 122-2 and 122-4-122-15 that needs to be maintained. While the memory device 120-3 is inaccessible in terms of core memory utilization, it may be accessible for other purposes. For example, the memory device 120-3 can be accessed in case of register read and write operations like ‘Read Status Register’ and ‘Write Configuration register’. The contents of the temporary cache 122-3 can be changed at any time, or modified in part or in whole depending on the memory controller 110. If the temporary cache 122-3 is not needed any more, then it can be used as a page buffer much like the other page buffers. It is the responsibility of the memory controller 110 to remember which page buffers are being used as a temporary cache. In the event that data needs to be read or written from one of the inaccessible memory devices, it is possible to move the contents of the page buffer of the inaccessible device to the page buffer of another device that is not currently requiring access.
FIG. 6 shows the system of FIG. 3A performing data recovery (read back) from the temporary cache 122-3. The data recovery includes a data path as indicated by 333, 334, 336, 337 and 338. In this example, that the data is read from the temporary cache 122-3 of the third memory device 120-3 having the address “0010” to the data storage 112 of the flash memory controller 110. The data can be read out using the ‘Burst Data Read’ OP code. This data can optionally then be written to another page buffer.
FIG. 7 shows an example of signaling for the data recovery from the temporary cache 122-3 of the third memory device in the system shown in FIG. 6. A CSI signal SCSI and a DSI signal SDSI are sent from the memory controller 110 along with a CI signal SCI. The CSI signal, the DSI signal and the CI signal are propagated through the series-connected devices. The propagated CSI signal, DSI signal and CI signal are shown as SCSi, SDSi and SCi, respectively. As such, a read request is transmitted by asserting the CSI signal SCSi while the CI signal SCi carries the command. The command traverses the first and second memory devices 120-1 and 120-2 to get to the third memory device 120-3 addressed by the read request. In response to the read request and the assertion of the input CS signal SCS3 and DS signal SDS3, the memory device 120-3 provides the data as the output CI signal SC3 from the temporary cache 122-3. The data is propagated along the data path 333, 334, 336, 337 and 338 to the data storage 112 of the memory controller 110. The memory controller 110 receives the read data via the output CI signal SC16 from the last device 120-15.
FIG. 8 shows a method for using a page buffer as a temporary cache in the system of FIG. 3A. This method can be implemented in a memory controller, for example by the memory controller 110 shown in FIG. 3A. Referring to FIGS. 3A and 8, the memory controller 110 issues a ‘Burst Data Load’ OP code with data along with a device address for a designated memory device (step 9-1). The third device 120-3 is designated and selected in accordance with the device address DA. The data is stored in the page buffer 122-3 of the selected memory device 120-3 (step 9-2). Later, when the data stored in the temporary cache is required to be read back, the memory controller 110 sends the read command. The command containing the OP code for ‘Burst Data Read’ is issued, together with the DA (“0010”). Upon device address match determination, the memory device 120-3 processes the command and the data is read (step 9-3) and the read data is sent back to the memory controller 110 through the remaining memory devices.
FIG. 9A shows the system of FIG. 3A wherein two data transfers are performed for temporary cache for data. In this particular example, the same data is temporarily stored in the page buffers of two memory devices. FIG. 10 shows timing for the data transfers in the system shown in FIG. 9A. FIG. 11 shows an example method for using the page buffers shown in FIG. 9A. FIG. 9B illustrates the data transfers shown in FIG. 9A;
Referring to FIGS. 3A, 9A, 9B and 10-11, the memory controller 110 issues a ‘Burst Data Load’ OP code with data along with a device address DA (0000) for a designated memory device (step 19-1). The first device 120-1 is designated and selected in accordance with the device address DA. The data is stored in the page buffer 122-1 of the selected memory device 120-1 (step 19-2). Then, the memory controller 110 determines whether more cache needs (step 19-3). In this case, another cache is necessary (YES at step 19-3), the memory controller 110 issues again a ‘Burst Data Load’ OP code with data along with a device address DA (0010) for a designated memory device (step 19-1). The third device 120-3 is designated and selected in accordance with the device address DA. The data is stored in the page buffer 122-3 of the selected memory device 120-3 (step 19-2). No more cache is necessary (NO at step 19-3) and temporary store of the data is completed.
Later, when the data stored in any one of the temporary caches is required to be read back, the memory controller 110 sends the read command. The command containing the OP code for ‘Burst Data Read’ is issued, together with the device address for designating the temporary cache. For example, the data temporary stored in the page buffer 122-1 of the first memory device 120-1 is read back. In such a case, the device address DA (“0000”) with the read OP code is sent by the memory controller 110. Upon device address match determination, the memory device 120-1 processes the command and the data is read and the read data is sent back to the memory controller 110 through the remaining memory devices (step 19-4). If reading back of the data temporarily stored in one page buffer is sufficient, no more reading will be necessary (NO at step 19-5) and reading back operation is completed. However, for any reason, another reading back of the data is required (YES at step 19-5), the memory controller 110 sends the command containing the device address DA (0010) and the OP code for ‘Burst Data Read’. The data temporarily stored in the page buffer 122-3 of the third memory device 120-3 is read back (step 19-4). If the second reading back of the data temporarily stored in the page buffer is sufficient, no more reading will be necessary (NO at step 19-5) and reading back operation is completed.
It would be apparent that the data from data storage 112 of the memory controller 110 can be temporarily stored in more than two temporary caches. The data can be read back from any one of the temporary caches.
Alternatively, two or more different data can be loaded in two or more temporary caches.
FIG. 12A shows the system of FIG. 3A wherein three data transfers are performed for a temporary cache. FIG. 12B shows the data transfers shown in FIG. 12A. FIG. 12C shows timing for the data transfers in the system shown in FIG. 12A.
Referring to FIGS. 11, 12A, 12B and 12C, the data storage 112 of the memory controller 110 store data (of, e.g., 10K bytes) comprised of Data 1 (4K bytes), Data 2 (4K bytes) and Data 3 (2K bytes). The capacity of each page buffer is smaller than the data to be temporarily cached (i.e., 10K bytes). Therefore, one page buffer is not enough for temporary cache for the data.
Data 1, 2 and 3 are sequentially stored in three temporary caches. The memory controller 110 issues a command containing a device address DA (0000), a ‘Burst Data Load’ OP code and Data 1 (step-19-1). The first device 120-1 is designated and selected in accordance with the device address DA. Data 1 is stored in the page buffer 122-1 of the selected memory device 120-1 (step 19-2). Then, the memory controller 110 determines whether more cache needs (step 19-3). In this case, another cache is necessary (YES at step 19-3), the memory controller 110 issues a command containing a device address DA (0001), a ‘Burst Data Load’ OP code and Data 2 (step 19-1). The second device 120-2 is designated and selected in accordance with the device address DA. Data 2 is stored in the page buffer 122-2 of the selected memory device 120-2 (step 19-2). Again, the memory controller 110 issues a command containing a device address DA (0010), a ‘Burst Data Load’ OP code and Data 3 (step 19-1). No more cache is necessary (NO at step 19-3) and temporary stores are completed.
In the data recovery operation, Data 1, 2 and 3 temporarily stored in the page buffers 122-1, 122-2 and 122-3 are sequentially read and back to the data storage 112 of the memory controller 110.
The memory controller 110 sends a command containing a device address DA (0000) and OP code for ‘Burst Data Read’. Upon device address match determination, the first memory device 120-1 processes the command and Data 1 temporarily stored in the page buffer 122-1 of the first memory device 120-1 is read and the read data is sent back to the memory controller 110 through the remaining memory devices (step 19-4). More reading back is required (YES at step 19-5), step 19-4 is repeated. Thus, the memory controller 110 sends a command containing a device address DA (0001) and OP code for ‘Burst Data Read’. Upon device address match determination, the second memory device 120-1 processes the command and Data 2 temporarily stored in the page buffer 122-2 of the second memory device 120-2 is read and the read data is sent back to the memory controller 110 through the remaining memory devices (step 19-4). Similarly, the memory controller 110 sends a command containing a device address DA (0010) and OP code for ‘Burst Data Read’. Upon device address match determination, the third memory device 120-3 processes the command and Data 3 temporarily stored in the page buffer 122-3 of the second memory device 120-3 is read and the read data is sent back to the memory controller 110 through the remaining memory devices (step 19-4). No more reading is necessary (NO at step 19-5) and reading back operation is completed.
Another scenario is that while the capacity of the data storage 112 is smaller than that of each page buffer, the character of Data 1, 2 and 3 are different (e.g., instruction command, data value to be stored in the flash memory) and Data 1, 2 and 3 are separately cached. In such a scenario, process is the same as described above.
In some embodiments of the present invention, the systems described herein are implemented using a flexible modular command structure, example details of which have already been provided. Further example details are provided in this section with reference to FIGS. 13 through 21. It is to be understood that the details provided in this section are very specific for exemplary purposes only.
FIG. 13 is a table of an example command set for flash memory with modular command in byte mode. The table includes 14 operations: Page Read, Page Read for Copy, Burst Data Read, Burst Data Load Start, Burst Data Load, Page Program, Block Erase Address Input, Page-pair Erase Address Input, Erase, Operation Abort, Read Device Status, Read Device Information Register, Read Link Configuration Register, and Write Link Configuration Register. Each operation has a command including a Device Address (DA) (1 Byte) and an Operation (OP) Code (1 Byte). Some commands include a Row Address (3 Bytes), a Column Address (2 Bytes), and some commands include Input Data (1 to 2112 Bytes). ‘X’ is ‘0h’ for “Bank 0”. ‘X’ is ‘1h’ for “Bank 1” where it is assumed for this specific example that each device has two memory banks. More generally each device has at least one memory bank. For the last command in the table, namely the write link configuration (broadcast), the device address is set to “FFh” to indicate a “broadcasting” command.
FIG. 14 is an example operation table. The table includes modes for each of a plurality of combinations of /RST (complement of a reset signal), /CE (complement of a chip enable signal), CSI (command strobe input), and DSI (data strobe input). The modes include Command Data Packet, Read Data Packet, NOP (NO Operation), Standby, and Reset.
All commands, addresses, and data are shifted in and out of the memory device, starting with the most significant bit (MSB). Command input (CI) is sampled at the positive or negative clock edge (i.e., at the crossing point of clocks—CK and /CK) while the command strobe input (CSI) is “high”. Each command includes a 1-byte device address (DA) and 1-byte OP code and/or column-address/row-address/data-input bytes if necessary. Once the CSI transits logic “high”, the 1-byte DA (Device Address) is shifted into a DA register, and then the 1-byte OP code is shifted into an OP code register. In so doing, the most significant bit (MSB) starts first on CI and each bit is latched at the crossing of CK and /CK while CSI is logic-HIGH state. However every input sequence in byte mode starts at a rising edge of CK (=falling edge of /CK). Depending on the command, the OP Code are followed by address bytes, data bytes, both or none as shown in FIG. 13. For this example, the address cycle has a 2-byte column address and 3-byte row address. FIG. 15 shows a definition of an example command and address format including the position of each bit.
For the memory devices connected in-series, a special device address (=FFh) is assigned for “Broadcast” operation. More generally, the address that is defined for broadcast mode operation can be defined on an implementation specific basis. This “Broadcast Device Address” may be used with any command. However, using the broadcast device address (FFh) along with the “read-type” commands is not recommended because the read data from the last device is the only valid output data.
In some implementations, the signal bus on a modular command Flash device is fully multiplexed as command, address and data all share the same pin(s). The CSI signal's logic-high state validates the Command Input (CI) which can be an n-bit wide signal containing multiplexed command/address/data information for the memory device. If the CSI signal stays in logic-low state, device ignores signal inputs from CI pins. The command input sequence normally consists of one-byte DA (Device Address) latch cycles, one-byte command latch cycles, address latch cycles (=3-bytes for row address or 2-bytes for column addresses) and/or data-input latch cycles up to 2,112 bytes. In 1-bit link mode, four clock-cycles at DDR (double data rate) make one byte of a serial packet. In 2-bit link mode, two clock-cycles at DDR (double data rate) make one byte of a serial packet. In 4-bit link mode, one clock-cycle at DDR (double data rate) makes one byte of a serial packet. Every set of command instructions may be followed by two extra CK and /CK transitions after CSI makes a HIGH to LOW transition. In some embodiments, an extra number of CK and CK transitions after SCSi transitions to low are used that are equal in number to 2+ the number of devices in the architecture with devices connected together in-series. Every input sequence defined in FIG. 13 is “byte-based”, which means that SCSi and SCi should be valid for the unit of 8-latch cycles (=4 clock cycles at double data rate). If SCSi makes a HIGH to LOW transition before the completion of byte, corresponding command and/or address sequences will be ignored by device. For the case of data input sequence, the last incomplete byte of input data will be ignored, but prior complete byte(s) of input data will be valid.
FIG. 16 is an example timing diagram showing basic input timing. All DA/Command/Address/Data-Inputs are asserted continuously through CI port(s) and captured on the crossing of CK and /CK when /CE is “low” and SCSi is “high”. The input data is shifted into the memory device, most significant bit (MSB) first on SCi, each bit being latched at the crossing of CK and /CK. An input sequence of bit streams is shown in FIG. 17. Every input sequence in byte mode starts at rising edge of CK as shown. Any input with incomplete byte will be ignored.
FIG. 18 is an example timing diagram showing basic output timing. The output on SC(i+1) is synchronously shifted out at the crossing of CK and /CK when /CE is “low”, and SDSi is “high”. FIG. 19 shows an example output sequence in byte mode. The output data is shifted from the memory device, most significant bit (MSB) first on SC(i+1), each bit being synchronized at the crossing of CK and /CK. The SDSi signal is activated referenced to the rising edge of CK so that every output sequence in byte mode starts at rising edge of CK with 1 clock read latency (=tOL) as shown in FIG. 18.
Two representative commands to show the feature of modular commands are described below, namely a Page Read (DA and 0×h) and a Burst Data Read (DA and 2×h) command. FIG. 20 shows a flowchart involving the use of these commands, and FIG. 21 shows an example command sequence.
Referring to FIGS. 20 and 21, to enter the Page Read mode, at step 20-1 the memory controller issues the PAGE READ (DA and 0×h) command to the command register via SCi along with three row address bytes. Issuing DA and 0×h to the command register starts the address latch cycles at step 20-2. Three bytes of row address are input next. The internal page read operation starts once the address latch cycles are finished. The 2,112 bytes of data within the selected page are sensed and transferred to the page buffers in less than tR (transfer time from cell array to page buffers). The status register can be checked at step 20-3. After tR, a BURST DATA READ (DA and 2×h) command (described in further detail below) along with two bytes of column address can be issued at step 20-4 and then the SDSi signal can be enabled in order to read out page buffers' data, starting from the given column address, via SC(i+1) until SDSi goes low. If a user wants to monitor the internal page read status to determine whether the transfer from the cell array to page buffers is complete or not, the READ DEVICE STATUS (DA and D0h) command can be issued. Modular command flash has an 8-bit status register that the software can read during device operation.
The core access operations such as page read, page program and block erase take long time and their processing times are varied according to PVT (ProcessNoltage/Temperature) change. So, whenever issuing core access commands, a user can monitor the status of each operation after asserting command without interrupting internal operations. The other purpose of the status register is to check whether or not the page program and block erase are performed without fail. In case of fail, a new row position is determined by the memory controller and it issues a new command containing new row address to write the same data that was written to the old row location that failed to be written. Without monitoring the status register, the memory controller does not know that the program and erase operations are done without fail.
After READ DEVICE STATUS (DA and D0h) command, using DSI, all 8-bit status is read from the status register until DSI goes to low. After the BURST DATA READ (DA and 2×h) command has been issued and then DSI goes to high, the serial output timing as shown in FIG. 21 will result in outputting data at step 20-5, starting from the initial column address. The column address will be automatically increased during outputting data. At step 20-6, there is ECC generation. If the ECC is verified at step 20-7, then the page read is completed. Otherwise, at step 20-8 there is an error.
The BURST DATA READ (DA and 2×h) command referred to above enables the user to specify a column address so the data at the page buffers can be read starting from the given column address within the selected page size while SDSi is high. The burst data read mode is enabled after a normal PAGE READ (DA and 0×h) command and page loading time (=tR). The BURST DATA READ (DA and 2×h) command can be issued without limit within the page. Every BURST DATA READ command can have same or different column address from the previous BURST DATA READ command. Only data on the current page buffers can be read. If a different page is to be read, a new PAGE READ (DA and 0×h) command should be issued. And after tR, a new BURST DATA READ (DA and 2×h) command can be issued to access new page data.
In the embodiments described above, the device elements and circuits are connected to each other as shown in the figures, for the sake of simplicity. In practical applications of the present invention, elements, circuits, etc. may be connected directly to each other. As well, elements, circuits etc. may be connected indirectly to each other through other elements, circuits, etc., necessary for operation of the memory devices or apparatus. Thus, in actual configuration of devices and apparatus, the elements and circuits are directly or indirectly coupled with or connected to each other.
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

## Claims

1. A method for use in a system comprising a serial interconnection of first to N-th memory devices connected in-series and a memory controller configured to communicate with the interconnection, N being an integer greater than one, each of the N memory devices including a memory for storing data and being associated with a device identification, each of the N memory devices being selectable based on the device identification, each of the N memory devices being configured to transfer an enable signal received at its enable input to a successive memory device of the serial interconnection, each of the N memory devices being configured to transfer a command signal received at its signal input to the successive memory device based on device selection determination and in response to the enable signal received at its enable input, each of the N memory devices being configured to receive a clock signal at its clock input and to perform operations in response to the received clock signal, the method comprising:
at the memory controller
sending a command signal to the first memory device; the command signal including a device address identification for device selection, an operation instruction and a memory address identification;
wherein, the device address identification, the operation instruction and the memory address identification form a modular command structure, the modular command structure being a byte basis,


at an i-th memory device of the serial interconnection, i being 1≦i≦N
receiving the command signal sent by the memory controller or transferred from a previous memory device, the receiving the command signal being enabled by the enable signal received at the enable input of the i-th memory device,
determining whether the i-th memory device is selected based on the device address identification included in the received command signal and the associated device identification,
in a case of determination where the i-th memory device is selected,
providing a selection determination for processing, and
in response to the selection determination for processing, processing the operation instruction included in the received command signal to access the memory included in the i-th memory device in accordance with the memory address identification included in the received command signal,

in a case of determination where the i-th memory device is not selected, forwarding the received command signal including the device address identification, the operation instruction and the memory address identification formed in a modular command structure to the signal input of the successive memory device.

2. The method of claim 1, wherein the operation instruction represented by an operation code.

3. The method of claim 1, wherein the operation instruction comprises a data write instruction.

4. The method of claim 3, wherein at the memory controller,
sending the command signal including the device address identification for device selection, the data write instruction, the memory address identification, data to be written,
wherein, the device address identification, the data write instruction, the memory address identification and the data form a modular command structure.

5. The method of claim 4, wherein at the i-th memory device, the processing the operation instruction comprises:
in response to the selection determination for processing, processing the data write instruction to write the data included in the received command signal, the data being written in the memory in accordance with the memory address identification included in the received command signal.

6. The method of claim 1, wherein the operation instruction comprises a data read instruction.

7. The method of claim 6, wherein at the memory controller,
sending the command signal including the device address identification for device selection, the data read instruction and the memory address identification,
wherein, the device address identification, the data read instruction and the memory address identification form a modular command structure.

8. The method of claim 7, wherein at the i-th memory device, the processing the operation instruction comprises:
in response to the selection determination for processing, processing the data read instruction included in the received command signal, the data stored in the memory being read out from the memory in accordance with the memory address identification included in the received command signal.

9. The method of claim 1, wherein at the i-th memory device, the determining whether the i-th memory device is selected comprises:
comparing the device address identification of the command signal to the device address associated with the i-th memory device.

10. The method of claim 9, wherein the comparing comprises:
determining whether the device address identification of the command signal matches the device address associated with the i-th memory device to provide a determination result.

11. The method of claim 10, wherein the determination result is provided as the selection determination for processing, when:
the device address identification of the command signal is identical to the device address associated with the i-th memory device.

12. A method for use in a system comprising a serial interconnection of first to N-th memory devices connected in-series and a memory controller configured to communicate with the interconnection, N being an integer greater than one, each of the N memory devices including a memory for storing data and being associated with a device identification, each of the N memory devices being selectable based on the device identification, each of the N memory devices being configured to transfer an enable signal received at its enable input to a successive memory device of the serial interconnection, each of the N memory devices being configured to transfer a command signal received at its signal input to the successive memory device based on device selection determination and in response to the enable signal received at its enable input, each of the N memory devices being configured to receive a clock signal at its clock input and to perform operations in response to the received clock signal, the method comprising:
at the memory controller
sending a first command signal to the first memory device; the first command signal including a first device address identification for device selection, a data write instruction, a memory address identification and data to be written,
wherein, the first device address identification, the data write instruction, the memory address identification and the data form a modular command structure,


at an i-th memory device of the serial interconnection, i being 1≦i≦N
receiving the first command signal sent by the memory controller or propagated from a previous memory device, the receiving the first command signal being enabled by the enable signal received at the enable input of the i-th memory device,
determining whether the i-th memory device is selected based on the first device address identification included in the received first command signal and the associated device identification,
in a case of determination where the i-th memory device is selected,
providing a selection determination for processing, and
in response to the selection determination for processing, processing the data write instruction included in the received first command signal, the data included in the received first command signal being written in the memory included in the i-th memory device in accordance with the memory address identification included in the received first command signal,

in a case of determination where the i-th memory device is not selected, forwarding the received first command signal including the first device address identification, the data write instruction, the memory address identification and the data formed in a modular command structure to the signal input of the successive memory device,


at the memory controller
sending a second command signal to the first memory device; the second command signal including a second the device address identification for device selection, a data read instruction and the memory address identification,
wherein, the second device address identification, the data read instruction and the memory address identification form a modular command structure,


at a j-th memory device of the serial interconnection, j being 1≦j≦N
receiving the second command signal sent by the memory controller or propagated from a previous memory device, the receiving the second command signal being enabled by the enable signal received at the enable input of the j-th memory device,
determining whether the j-th memory device is selected based on the second device address identification included in the received second command signal and the associated device identification,
in a case of determination where the j-th memory device is selected,
providing a selection determination for processing, and
in response to the selection determination for processing, processing the data read instruction included in the received second command signal, the data previously written in the memory included in the j-th memory device in accordance with the memory address identification included in the received second command signal,

in a case of determination where the j-th memory device is not selected, forwarding the received second command signal including the second device address identification, the data read instruction and the memory address identification formed in a modular command structure to the signal input of the successive memory device.

13. The method of claim 12, wherein:
at the memory controller, the sending the first command signal is performed before the sending the second command signal.

14. The method of claim 13, wherein:
after the sending the first command signal to the first memory device by the memory controller, the i-th memory device performs the receiving the first command signal and the determining whether the i-th memory device is selected.

15. The method of claim 14, wherein:
at the memory controller, after sending the first command signal, the sending the second command signal is performed.

16. The method of claim 15, wherein:
after the sending the second command signal to the first memory device by the memory controller, the j-th memory device performs the receiving the second command signal and the determining whether the j-th memory device is selected.

17. A method for use in a system comprising a serial interconnection of first to N-th memory devices connected in-series and a memory controller configured to communicate with the interconnection, the memory controller including a storage element for storing data, N being an integer greater than one, each of the N memory devices including a temporary store element for temporarily storing data and being associated with a device identification, each of the N memory devices being selectable based on the device identification, each of the N memory devices being configured to transfer an enable signal received at its enable input to a successive memory device of the serial interconnection, each of the N memory devices being configure to transfer a command received at its signal input to the successive memory device based on device selection determination and in response to the enable signal received at its enable input, each of the N memory devices being configured to receive a clock signal at its clock input and to perform operations in response to the received clock signal, the method comprising:
at the memory controller
sending a first command signal to the first memory device; the first command signal including a first device address identification for device selection, an operation instruction for data storing and first data read from the storage element included in the memory controller,
wherein, the first device address identification, the operation instruction and the first data form a modular command structure,


at an i-th memory device of the serial interconnection, i being 1≦i≦N
receiving the first command signal sent by the memory controller or propagated from a previous memory device, the receiving the first command signal being enabled by the enable signal received at the enable input of the i-th memory device,
determining whether the i-th memory device is selected based on the first device address identification included in the received first command signal and the associated device identification,
in a case of determination where the i-th memory device is selected,
providing a selection determination for data storing, and
in response to the selection determination for data storing, storing the first data included in the received first command signal in the temporary store element included in the selected i-th memory device;

in a case of determination where the i-th memory device is not selected, forwarding the received first command signal including the first device address identification, the operation instruction and the first data formed in a modular command structure to the signal input of the successive memory device.

18. The method of claim 17, wherein after sending the first command signal,
at the memory controller
sending a second command signal to the first memory device; the second command signal including a second device address identification for device selection, the an operation instruction for data storing and second data read from the storage element included in the memory controller,
wherein, the second device address identification, the operation instruction and the second data form a modular command structure,


at an j-th memory device of the serial interconnection, j being 145N
receiving the second command signal sent by the memory controller or propagated from a previous memory device, the receiving the second command signal being enabled by the enable signal received at the enable input of the j-th memory device,
determining whether the j-th memory device is selected based on the second device address identification included in the received second command signal and the associated device identification,
in a case of determination where the j-th memory device is selected,
providing a selection determination for data storing, and
in response to the selection determination for data storing, storing the second data included in the received second command signal in the temporary store element included in the selected j-th memory device;

in a case of determination where the j-th memory device is not selected, forwarding the received second command signal including the second device address identification, the operation instruction and the second data formed in a modular command structure to the signal input of the successive memory device.

19. The method of claim 18, wherein after sending the second command signal,
at the memory controller
reading back the first and second data stored in the temporary store elements included in the i-th and j-th memory devices.

20. The method of claim 19, wherein after sending the second command signal,
at the memory controller
freeing up space in the storage element storing the first and second data.

21. The method of claim 20, wherein after the freeing up space in the storage element,
at the memory controller
reading back the first and second data stored in the temporary store elements included in the i-th and j-th memory devices, the read backed first and second data being re-stored in the storage element of the memory controller.