TW577079B - Circuit and method for performing variable width searches in a content addressable memory - Google Patents

Abstract

A content addressable memory (CAM) for generating intermediate search results in a search on a stored data word sequence. The CAM comprises a plurality of rows of CAM cells each for storing a data word in the data word sequence; a plurality of match lines each coupled to a corresponding row of CAM cells, each for generating a corresponding match line signal. A priority encoder is coupled to the match line for generating a match address in response to a match line signal; and a plurality of logic circuits, each coupled to corresponding match lines for selectively coupling the match line signal to the priority encoder in response to an instruction signal, the instruction signal for instructing the CAM to generate a match address output on a new search or on a continuation of a previous search, such that portions of the data word sequence occurring at any intermediate location within the sequence provides match results in response to input search data which are equivalent to portions of the stored data word sequence.

Description

577079 A7 _- _ B7 V. Description of the invention (彳) The present invention outlines the scope of the content addressable memory (CAM) and more specifically a circuit and a CAM for searching for search data with variable block width. method. BACKGROUND OF THE INVENTION Content addressable memory CAM is a memory device in which data is accessed and modified based on the content of the stored data rather than the location where the data is stored. Generally speaking, a typical CAM search operation includes receiving a search data block and comparing the search data block with all the items in the CAM to determine whether there is a single match between the search data block and the items in the CAM. Multiple matches or no matches. Each storage location in the cam column is connected to a matching line, which indicates the result of a match or mismatch between the stored data block and the search block. All match lines indicating the match status are generally processed by a priority encoder to determine a match address with the highest priority provided as the output of the CAM. Each data block and matching line combination has a unique N-bit address in the CAM. Therefore, as many as 2N matching lines are activated for any one search cycle. As mentioned above, CAM generally includes a priority encoder to generate N-bit addresses corresponding to the valid matching lines of the highest priority. This N-bit address can be used for network applications such as Internet Protocol IP routing table lookups, compression and decompression, and full associative cache memory implementation in microprocessor systems. application. Ternary CAM is widely used in network applications because it can store logic "0", logic "1", and "optional," state. CAM is available in 72-bit and 144-bit data Chinese National Standard (CNS) A4 specification (210 X 297 mm) 5. Description of the invention (2) Generally available in the width and the latest 288-bit width. Generally, 72-bit storage mode is used to store data in network applications. The medium access controller MAC address of the Layer 2 bridging table, and the Layer 3 Internet Protocol routing table is stored in 144-bit mode Each Internet Protocol routing table entry contains the data source address, data source port, destination address, destination port, and some kind of Quality of Service (QOS) or Type of Service T0S). In the CAM that supports two data widths, two types of tables can be maintained, thereby reducing the system cost and allowing the two functions to use a common CAM resource. When the search data width is known in advance, this CAM Useful, but in applications such as Uniform Resource Locator URL lookup tables, the search data width is generally long and undetermined. The current variable data width CAM is still limited to a single predetermined width. Therefore, the use of CAM for this purpose has not received much support. As mentioned above, it would be very useful to store URLs in CAM to speed up the network traffic flow with frequently accessed global web pages and effectively handle web cache memory. If a very wide CAM (several hundreds to thousands of bits width) that can handle most URL lengths can be implemented, a lot of storage space will be wasted when storing general or short URLs. In this case Using the same CAM for bridging or routing items will become a waste. So, although variable preset block width CAM does exist, there is still a need to support an arbitrary block width search and be able to use one or more types at any time. CAM to switch between search. In addition, different word width items should be -5- This paper size applies Chinese National Standard (CNS) A4 specifications (210 X 297 (Mm) 577079 A7 _ B7 __ V. Description of the invention (3) Stored in CAM blocks with arbitrary boundaries so that the entire CAM can be used without any unused or wasted gaps between projects. Granted to Pereira U.S. Patent No. 6,252,789 et al. Proposes an example of a system for searching for a block that is wider than a predetermined block width of the system stored in the CAM. Pereira describes a circuit that allows a data block chain wider than the width of a CAM column to be stored and searched in one or more CAM columns. As a result, a wider block search can be performed with a CAM that is physically organized into multiple smaller blocks. In Pereira, a sequence of one or more data blocks is stored in one or more CAM grid rows. Each column has accompanying wiring and width extension logic. The width extension circuits are connected to each other and each has a carry input, a carry output, and a match line output to determine how to provide a matching result to the priority encoder and to provide a matching result to each other. A control signal generated by an instruction decoder is provided to each width expansion logic circuit to decide when to provide the first, subsequent and last blocks in the data block chain and compare them with the data stored in the CAM. If a search data block having a predetermined block width of the system is provided, the matching output signal in each width expansion logic circuit is provided to the priority encoder and the carry output signal is maintained in a non-operation state. But if the search data block provided to the CAM is the first block of a multi-block chain, the output signals of each matching line are set to indicate a mismatch-meaning it is suppressed 'and each carry output signal is propagated to One width extension circuit at a time. If the search data block provided to the CAM is a trailing block in a multiple block key, then the output signals of each match line indicate a mismatch and each carry output signal is generated by a logical combination of the carry input signal and the result of the middle match line And similarly propagated to the next width extension circuit. If provided to the CAM2 search data block • 6- This paper size is suitable for household use (CNS) A4 size (210 X 297 mm) ----

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Line 577079 A7 __ B7 V. Description of the Invention (4) is the last block of a multiple block chain, and the output signal of each match line indicates a match when the logical combination of the carry input signal and the result of the middle match line is valid. As a result, the matching result will not be provided to the priority encoder before the last block in a multi-block data key has been compared with the CAM content. Therefore, this method is only effective in the exact matching multi-word search. As a result, one disadvantage of this method is that intermediate search results cannot be obtained. For example, in the case where the closest match occurs before the last phrase of the multi-word search data is ready, the closest match result will actually be obscured. Therefore, there is still a need for a CAM that is capable of searching for variable-width data words and in which the storage of data words effectively uses the CAM. SUMMARY OF THE INVENTION A content addressable memory (CAM) is used to generate intermediate search results in a search on a sequence of stored data blocks. The content addressable memory (CAM) includes a plurality of stored data block sequences. A CAM grid column of a data block, a plurality of matching lines each coupled to a corresponding CAM grid column and each generating a corresponding matching line signal, and a coupling line coupled to the matching line to generate a matching address in response to a matching line signal The priority encoder and a plurality of logic circuits each coupled to the corresponding matching line to selectively couple the matching line signal to the priority encoder according to a command signal, the instruction signal is used to instruct the CAM in a new search A matching address output is generated on a subsequent search of the previous or previous search such that the sequence portion of the data block that occurs at any intermediate position within the sequence provides a match result based on the input search data equivalent to the sequence portion of the stored data string. This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

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k 577079 A7 ___ B7 V. Description of the invention (5 Γ _ Brief description of the features and advantages of the present invention By way of example and by no means intended to limit the scope of the present invention, specific specific examples are described in the following drawings: FIG. 1 is a schematic simplified block diagram of a CAM array according to a specific example of the present invention; FIG. 2 is a time history chart showing a search timing of the CAM array of FIG. 1; Block diagram; Figure 4 is a timing diagram showing the timing of the matching lines of the CAM array of Figure 3; Figure 5 is an example data diagram showing a number of sequential address locations stored in the CAM of Figure 1; Figure 6 (a) and 6 (b) is a schematic diagram of the search data sequence applied to the CAM; Figs. 7 (a) and 7 (b) are time charts of the search operation using the search data in Figs. 6 (a) and 6 (b), respectively; Fig. 8 is a diagram showing data stored in a CAM according to another embodiment of the present invention; Fig. 9 is a search sequence diagram to be applied to the CAM data shown in Fig. 8; The data map in the CAM grid of the example; and FIG. 11 shows a specific embodiment according to the present invention. Schematic diagram of the circuit used to process the output of the matching line. Detailed description of the preferred embodiment. Similar numbers in the following represent similar structures in the figure. Please refer to FIG. 1, which shows that a specific example according to the present invention is organized into 128k X 72-bit single [128k X 72 non-9M] CAM array 100 This paper size is applicable to Chinese National Standard (CNS) A4 specifications (210X 297 mm) 577079 A7 B7 V. Description of the invention (6. 72-bit The word is accessed on a 72-bit data bus, which has three functions. · Provides 72-bit search data when performing a search operation; provides 72-bit written data to storage And read the 72-bit download items that have been stored in the table. The data bus is bidirectional and can accommodate these three functions. CAM includes a priority encoder and multiple match resolver (MMR) 120 Its operation and structure are described in US Patent Application No. 09/954, 074. This patent application is attached here for reference, but other traditional prioritized coding circuits can also be used instead Effect of the specific embodiment of the present invention. Basically, the priority encoder and multiple match resolver 120 receive all match line latch input and generates as output a highest priority match address.

During the search, the matching line latch 107 accompanying each matching line contains the search result of the comparison between the stored data of each item and the search data, which means " (match) in " (match) or " missing "(" Mismatch). The priority encoder and MMR (Multiple Match Resolver) 120 convert the 128k "? or " missing " indicator into a single one with the highest priority " in the highest priority " Sequential address. Storage locations are ordered from highest to lowest priority. In addition, a 'MATCH' bit indicating whether a match has occurred in the array is provided as output. In addition, a multiple match (MM) flag The marker is also provided as an output to indicate whether multiple matches have occurred. If there is no " (or match), the match bit is maintained at a logic " low " state. If there is " in at least one ", the MATCH bit will be set to a logical " high " state. If more than one " in " occurs in any particular search, then the match (MATCH) ) The bit will be set to logic " high " and multiple matching (MM) flag-9-This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

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Line 577079 A7 B7 Fifth, the invention description (7) mark will also be set to a logic " high " state. Please refer to Figure 2, which shows an example of a series of typical search jobs performed on a cam array 100. On the first rising edge 202 of the system clock signal CLK, the search data si is pushed into the cam by the clock. After about two and a half (2%) clock cycles 204, the result R1 of searching for a matching address (MA) is obtained. There is a single match at the CAM array output by MATCH = 1 and MM = 0. The result is obtained and latched on the third clock edge 206 by an external circuit (not shown), so this is called a delay 3 operation, which means that there are 3 system clocks between issuing a search command and obtaining the search result Cyclic delay. These clock cycles are needed internally by the CAM to lock in search data, format it to facilitate searching for a 'pre-charged match line, generate match results for each item, encode the most effective match, and drive output pins. Searching can be performed on each clock edge by implementing an internal pipeline architecture. The result of search 2 is "missing", so there is no matching address output. The result of searching S3 is multiple matching (set high state), so only the highest valid matching address R3 appears on the MA bus output. Please refer to Figure 3, which shows a small set of lattice arrays 32 of a ternary CAM 300. Each ternary lattice 322 contains two storage units for storing two bits labeled as bkl and for comparison Comparison transistor for storing data and searching data. The storage unit can be any type of Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM) grid. These types of memory are ternary data well known in the technical field as shown in Table I. Each column in the array forms a data block, and column -10- This paper size applies to China National Standard (CNS) A4 Specifications (210 X 297 mm)

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Line 577079 A7 B7 V. Invention description (Each grid within 8 is consumed to match line ML. Match lines MLQ-MLn are each coupled to Vdd via their respective pre-charged transistors. These transistors are powered by an effective logic "Low" ; Precharge signal PRE \ control. The grid rows in the array are coupled to their respective search lines S ° i; SO0; SI1; si0; SN1; SN〇 °

Table I b, data logic “0” logic “Γ“ arbitrary ”〇1 1 ο ο ο search data applied to each data column according to the same format, please refer to Figure 4, which shows the search operation of the CAM array of Figure 3 The timing chart of the control and data signals during the period. At the beginning of each clock cycle, the PRE \ signal is pulsed into a logic "low" state to charge each matching line ML to the positive power supply level Vdd. Then the search data is enabled on the search line. For example, three sequential searches are shown in Figure 4. The first is & strict, which is equivalent to searching with a logic " 丨 ''; the second is Sx () = 0. And sxl = l is equivalent to searching with a logic " 〇 "; the third is SxG = 0 and sxl = 0, equivalent to searching with a logic " random " state or actually covering the CAM grid So generally speaking for this better specific example, any CAM grid that stores a "random" state will not be able to discharge the matching line from its pre-charged level to "high" to the vdd state. Anything in the line The search data is a " arbitrary " (meaning Sx () = 0 , Sxl = 0) CAM grid will not be able to pull down the matching line. If the data stored in the grid matches the search data, the specific grid will not pull down the matching line. In the case of a grid in a grid or a CAM grid on a search line and the stored data is complementary to the search data (meaning bfcfl = Skl and bke = Sk0), -11 · This paper size applies the Chinese National Standard (CNS) A4 specification ( 210 X 297 mm) A7 B7 V. Description of the Invention (9) The matching line will be discharged to indicate a "missing". A " missing " on any grid coupled to its corresponding matching line will result in a " missing " of the entire column. In other words, the matching wires are pre-charged to a "order" situation and discharged by the "missing" situation on any associated grid. As shown in Fig. 1, when latched in the individual matching wire latches, ' Medium / Unsuccessful 4th & Supply Priority Encoder / Multiple Matching Resolver Circuit Section, This circuit section provides a single encoding address among the highest priorities. Items in the CAM are ordered from the lowest priority They are listed in order of highest priority. The general operation of the CAM array according to the specific examples of the present invention described above is used as a background to express the specific problems solved by the present invention. The invention briefly described in the background of the invention The specific problem to be solved is how to deal with the matching line result of the variable block width search. More specifically, it is highly desirable to provide search blocks with widths larger than the predetermined block width of the system stored in the CM array. Search results. As mentioned above, the traditional method described in the pereira patent only searches for exact matches between the bits of data and the bits stored in the relevant row of the CAM Provide a " match " result and provide this match result only after the entire search string has been searched. As a result, although a wide block (such as a URL) may have been stored in the CAM, when a search When executed on a part of a block, it cannot be used to identify a " match ". Other circuits so far have not been able to achieve this. This problem can also be described by referring to an example. Please refer to Figure 5, which An example character showing an array of symbols representing the contents of many rows of a CAM array that is used to store URLs of various lengths. Each element on the symbol array is -12-This paper size applies Chinese National Standard (CNS ) A4 specification (210X 297 mm) 577079 A7 B7 V. Description of the invention (1) The table requires one character of the URL of the 8-bit CAM. Blank characters are used in some places in the drawing to allow exact matching to occur. So the structure shown in Figure 5 is equivalent to a 72-bit wide CAM array. From this example, it can be seen that various items in the CAM array can correspond to continuous web pages accessed by the user. If the user has previously been in & qu ot; www · mosaid. com / licensing " to access a URL stored in the CAM, and the next time the user wishes to simply access the www.mosaid.com " webpage, unless the precise URL is already stored In the CAM, otherwise a matching address will not be generated in the CAM. The result of this exact matching requirement is that every URL that a user may need to access at the same website must be entered into the CAM to ensure an exact match. This is a waste of CAM space. In other words, suppose that the addresses stored in columns 0 and 1 are not addresses " www · mosaid. Comfr but correspond to " www · mosaid · com / ip " and the user wants to save Take " www. Mosaid. Com ". The prior art method proposed in the patent '789 does not output a matching address-even if a part of the 72-bit byte corresponding to "www. Mosai" has multiple matches in the address columns 0, 2 and 5. The invention therefore provides a solution to this problem. According to a specific example of the present invention, a search data string having a block width wider than a system predetermined block width stored in a CAM is divided into a group of blocks having a system predetermined width and sequentially searched in the CAM. Intermediate search results are provided to priority encoders and multiple search parsers as soon as each search is completed. Once the last word in the word group is searched, the user can determine which is the best match based on the intermediate search results and continue the search in a smaller range if necessary. -13- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

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577079 A7 B7 V. Description of the Invention (11) The advantages of the modified CAM can be explained by referring to the exemplary search data input added to the CAM content (shown in Figure 5) shown in Figure 6 (a). For data item D5, blank characters or π random "characters can be stored according to how to search for CAM-such as exact matching or partial matching. These characters can be registered by CAM users when the content of CAM is initialized Write. Figure 7 (a) shows from the user's point of view the search schedule that provides intermediate results during the search operation according to the present invention corresponding to the data search in Figure 6 (a). Instruction decoder (not shown) in the CAM Receives each successive search instruction and generates instruction bits corresponding to each search word to indicate whether the 72-bit search word represents a new search operation or a subsequent search operation. Please refer to FIGS. 6 (a) and 7 (a) Suppose the search input that the user wants to access is the URL "www.mosaid.com/1icensing/patents_role.htm" o This URL is divided into five 72-bit search words D as shown in Figure 6 (a) Bu D5. Each 72-bit search block D of the search input is connected to the same corresponding instruction block (INST) to the CAM at the rising edge of the clock signal. One bit (C0NT / NEW) indicates that its corresponding search phrase is a new search The search phrase is also a search phrase for subsequent searches. The first 72-bit search phrase D1 containing part of the URL " www. Mosai " results in addresses 0, 2 and 5 based on the contents of the CAM array shown in FIG. 5 Multiple matching at the location. The CAM circuit determines that the MATCH bit and the multiple matching flag (MM) are logical " high " status and outputs the highest priority matching address Μ = 0. For the subsequent corresponding partial URL " d · com / lie " for the 72-bit search block D2, a match is found at addresses 3 and 6 and the highest-priority matching address is output as MA = 3. When the third search is performed and D3 (including part After URL " ensing / pa ") is provided, no -14- This paper size applies Chinese National Standard (CNS) A4 specification (210 X 297 mm)

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577079

There are other matches. As a result, because two multiple matching results have occurred and there are no other matching results, the user is most likely to continue to perform a more elaborate search based on the multiple matches provided. Please note that different from the previous technical methods of suppressing these intermediate search results, the intermediate multiple matching result MA = 〇 was provided before the entire muscle search was performed. The user can judge the first and The second consecutive search phrase has a match that is part of the search turn. Users will find that this part of the matching table cannot have a URL address stored in the CAM and contain sufficient information needed to continue the search, and essentially find an exact match with a more accurate search μ sub-group. Based on this information, a second search sequence ′ ’WWW · saisai · com / l icensing " as shown in Fig. 6 (b) can be provided to the CAM. If the prior art method is used in this case, the search result will be "missing" because there is no direct match. However, in the case of the present invention, the second search sequence shown in Figure 6 (b) The result will be multiple matches with the highest priority match address as MA = 0, multiple matches with the highest priority match address as MA = 3, and the final single match as MA = 4. The latter is the best match URL. Here In the case, the unused trailing characters in the Quick Find data are set to "optional". Even if an exact match has been found, the CAM will not mask or suppress the partial match found as in the previous technical methods, so The user (not the CAM itself) can choose which addresses to ignore (MA = 0 and MA = 3)-if such addresses are not useful. The timeline of this search is shown in Figure 7 (10) or 'You may not store a [JRL in CAM but parse or divide the URL as shown in Figure 5 so that each segment is stored with a new CAM block position as the starting point, meaning that no segment crosses the CAM block boundary. Figure 8 shows the paper size according to this paper Applicable to Chinese National Standard (CNS) A4 specification (210X297 mm) 577079 A7 _ B7 V. Description of the invention (13 ~~ " Specify another specific storage structure to store URL " www. M〇saicL CQm / licensing / whatis a patent.htm " example. As shown in this figure, this structure saves 3 storage locations compared to the structure shown in Figure 5. Generally, if the stored URLs are closely related to each other, this analysis is used Data storage is advantageous. If the URLs to be stored in the CAM are not related to each other, this method will require more CAM space than the method described in Figure 5. And 'this method provides the most in a single search sequence To match without having to submit another set of input as in the previous example to resolve a multiple match. This method also provides the search flexibility of a precisely stored URL by inserting blank characters or by inserting " Random "characters so that a fragment creates a" quote. "Use the input shown in Figure 10 to search the data sequence" www.mosaid c () m / 1 icensing / patents_role · htm "to Figure 9 Data stored as shown A line search will result in a match Μ = 0 = 0, 1, 2, 3, and 4 followed by " missing ". Even if the input sequence is longer than the previous method, the result can be generated in a single conversion process, thereby avoiding A second search is required as described with reference to Figures 6 (b) and 7 (b). As shown in the example shown in Figure 9, it can be seen that the parsed data structure requires less storage because the prefix does not have to be repeated, Although this varies from case to case depending on the number of URLs sharing a common prefix. Another variation is a compressed data structure but a trailing " free " character search. In this case, items 0 to 4 are not required. Please refer to FIG. 11, which shows a circuit for processing a matching line signal to support variable block width searching according to a specific example of the present invention. -16- This paper size is suitable for Towel ® Standards (CNS) A4 (⑽X Tear Male I) " '577079 A7 ______B7 V. Description of the invention (14) The C0NT / NEW signal can be decoded by instructions or it can also be An independent bit in an instruction block. By latching the results of the combined search, not just the individual matching results, the block search can be interrupted for background work. For example, a form maintenance read or write job can be inserted between any search job shown in Figure 6 without affecting the multi-word search function. In the figure, the wiring signals MLO, ML1, ML2, ... are amplified by the inverter 125 and then input into the logic circuit 122. For each corresponding matching line output, the logic circuit 122 includes an AND-N0R gate 123 and an inverter 124. Each AND-N0R gate 123 receives the matching line output driven by the inverter 125 at an individual input, and is latched with a CONT / NEW logic signal and a lower priority matching line provided through the inverter 124 The combination of the results of the matching case is used as another input. The output of the AND-N0R gate 123 is provided as an input of the matching line D-type flip-flop 126, and the Q output of the flip-flop 126 is supplied to the priority encoder and the multiple matching parser 127. The operation of the logic circuit 122 will be described below. At the beginning of a new multiple block search, the first data block is added to the CAM array to generate a separate match indicator signal on the match line. At the same time, the appropriate bits are provided from the instruction decoder to generate the internal CONT / NEW control signal, which is set to logic " 〇 " to indicate that a new multiblock search is about to begin. As a result, D-type flip-flops lock up individual matching line results regardless of the state of adjacent matching line flip-flops. On the afterword block of the multiple block search, the internal CONT / NEW control signal is set to logic π 1 " by an appropriate decoding instruction block. Once C0NT / NEW has been set to logic " 1 " and the subsequent block indicating multi-block search is being searched, in order to allow any D-type flip-flop to record a match, -17-This paper scale applies to China Standard (CNS) A4 specification (210X 297 mm) 577079 A7 ______ B7 V. Description of the invention (15) The relevant matching line and the position of the previous matching line in the CAM array must be temporarily stored with a match in the previous cycle. As can be seen in Figure n, each D-type flip-flop receives the output of its associated AND-N0R gate 123, which combines the output of the relevant matching line with the lower priority provided by the previous D-type flip-flop through the inverter 124 The result of matching lines sequentially. In this way, the cumulative matching results of the matching lines from the lowest to the highest priority are propagated from one position to another during the multi-word search, thereby generating intermediate matches used by the traditional priority encoder and the multiple match parser. result. Although URLs are used as examples, almost any kind of search can be performed. For example, sentences and phrases can be stored in the same way. As shown in Figure n, the sentence is this a wretched demi bee "can be parsed and stored in six 72-bit words. In this case, suppose the user wants to search without necessarily starting from the item Phrase starting point—such as “demi bee”. The previous technical methods will not be able to provide a hint of where the information is located, because it is looking for an exact match. As a result, the result of partial matching is discarded, and it is lost to know that the CAM has One of the benefits of matching the searched data. But with the present invention, the ability to provide partial matching results will inform the user that the searched data is contained somewhere within CAJI-in this case, in words 4 and 5. There is With this result, the user can judge the importance of the found data for the desired search. In all of these examples, the benefits of getting partial matches before entering the entire input data string are clearly proven. Partially matching URLs provide information about Where can I find a good guide for a web page to the router. This is far more than -18 searching for successively abbreviated versions of the URL until a match occurs. -

This paper size applies to China National Standard (CNS) A4 specifications (210X297 male D 577079 A7 B7 V. Description of the invention (16). Although the invention is described above with specific specific examples of the invention and its explicit use, it is proficient in this technology Those skilled in the art can make many modifications without departing from the spirit of the present invention. The terms and notations used in the description of the present invention are used as descriptive terms rather than restrictive terms. The use of such terms and notations is not intended to exclude the shown and described. The features of the present invention or a part of them are equivalent, and please note that there may be various modifications within the scope of the present invention. -19- This paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm)

Claims (1)

577079 A8 B8 C8 __D8_________ VI. Patent Application Park _ ^ ~ 1 · A content addressable memory (CAM) is used to generate intermediate search results in the search of stored data word sequences. The CAM includes : (A) a plurality of CAM grid rows, each for storing a data block in the data block sequence; (b) a plurality of matching lines, each coupled to a corresponding CAM grid row, each for generating a corresponding Matching line signals; (c) a priority sequence encoder coupled to the matching line to generate a matching address in response to a matching line signal; and (d) a complex unitary logic circuit, each coupled to a corresponding matching line for An instruction signal selectively couples the matching line signal to the priority encoder, and the instruction signal is used to instruct the CAM to generate a matching address output for a new search or a subsequent search of the previous search, so that it occurs within the sequence The sequence portion of the data block at any intermediate position can provide a matching result based on the input search data equivalent to the sequence portion of the stored data string. 2. The addressable memory, as described in item 1 of the patent application scope, includes a matching latch coupled to a corresponding matching line to latch the matching line signal in response to a clock signal to latch a matching signal. 3. If the content of the second item of the scope of patent application can be addressed, for each matching line, the logic circuit is used to logically merge its matching line signal with the matching signal from the previous matching line to round out a signal. To the matching latch so that in a subsequent search, the matching latch only latches a match if the current search phrase matches and the previous match latch locks a match in the previous search. • 20- This paper size applies to China National Standard (CNS) A4 (210X 297mm)