Abstract:
Information for defining a structure of an address bit arrangement of a ROM portion of layout data is affixed, by means of text data as a discriminator, to a typical ROM cell portion indicating a characteristic of the address bit arrangement. Layout data including the affixed information is read in. ROM coordinate information and the text data are extracted. A ROM definition for generating a mask pattern is generated from the extracted ROM coordinate information based on ROM data. Thus, the layout information generating apparatus extracts the arrangement information and coordinate information of a ROM portion automatically, not manually, to generate a ROM definition, thereby considerably decreasing the number of steps to improve productivity.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and method of generating layout information, and, more particularly, to a layout information generating apparatus and method which generate information for writing ROM (Read Only Memory) codes and a mask option in a semiconductor integrated circuit incorporating a mask ROM. 
     2. Description of the Related Art 
     The background of the present invention will be discussed prior to a discussion of the related art. FIG. 1 is a diagram showing the structure for one bit of a 32-word ROM. Referring to FIG. 1, first, a description will be given of the structure of a ROM layout section which is the premise of the art relating to a layout information generating apparatus. 
     With reference to FIG. 1, of an address signal of five bits A 0  to A 4 , A 0  and A 1  are input to an X decoder  32  to select one of select signal line X 0  to X 3  in the X-coordinate direction. Likewise, A 2  to A 4  in the 5-bit address signal A 0 -A 4  are input to an Y decoder  31  to select one of select signal lines Y 0  to Y 7  in the Y-coordinate direction. A ROM is constructed by laying out cell blocks  33  at the intersections of the thus constituted select signal lines in the X-coordinate direction and the Y-coordinate direction to set ROM cells, and leading out the existence/non-existence of each cell block  33  or ROM cell as a bit output B 0 . 
     In this case, whether the cell block  33  is laid out when a logic value is “1” or when it is “0” is determined by the circuit structure and the fabrication process. In the following description, it is assumed that the cell block  33  is laid out when a logic value is “1” and it is not when the logic value is “0.” It is “ROM data” that is the original data of this layout and that has a sequence of “0” and “1” (for the length of the address). The ROM data is generally expressed by a hexadecimal (16) notation from the viewpoint of management. 
     A description will now be given of the structure of a mask option which is the premise of the art relating to a layout information generating apparatus. The “mask option” is an option which is the other portion than the ROM and which can be selected by a user. The mask option includes an option for whether or not a pull-up resistor is present, switching between pull-up and pull-down, etc. While this portion is intrinsically irrelevant to ROM data, the set value of the mask option is designated, together with input ROM data, in the case of a ROM-incorporated microcomputer product. 
     FIG. 2 is a diagram exemplifying the circuit structure of a part of a chip with a designated mask option portion. Referring to FIG. 2, a pull-up resistor  21  is preset, and it is determined if the pull-up resistor  21  should be reflected on the circuit, depending on whether or not a cell (hereinafter called “dummy cell”)  22  is to be generated. 
     When the presence of the pull-up resistor is designated by a mask option designation field in an input ROM code, the dummy cell  22  is laid out and the pull-up resistor is reflected on the circuit as shown in FIG.  3 . In the case of no pull-up resistor, the dummy cell  22  is not laid out and the pull-up resistor is not reflected on the circuit as shown in FIG.  4 . 
     A description will now be given of the structure of a ROM definition and a mask option definition which are the premise of the art relating to a layout information generating apparatus. 
     Laying out ROM cells and dummy cells for the mask option in accordance with ROM data previously requires the position and coordinate information of the ROM cells and mask option dummy cells for an input address. 
     In the case of the ROM structure which has been discussed referring to FIG. 1, the position (select signal line) and coordinate information of ROM cells with respect to an input from the input address A 0 -A 4  as shown in, for example, FIG.  5 . 
     The correlation shown in FIG. 5 is called a ROM definition which needs records by the number of ROM cells (one record consists of an address value and position information (select signal)). The memory capacity therefore becomes larger in proportion to the size of the ROM. 
     To reduce the memory capacity, an attempt has been made to compress a ROM definition by expressing the ROM definition in an array form by extracting and grouping ROM cells whose coordinate pitches and address pitches between adjoining ROM cells are identical. 
     Suppose that there is a ROM group consisting of 32 ROM cells as shown in FIG.  6 . The numerals in the individual cells in the diagram are addresses associated with the ROM cells. 
     FIG. 7 illustrates the compression of a ROM definition in consideration of adjoining ROM cells. The ROM definition, which should originally need a total of 32 ROM cell records, is compressed to the size of three records. Referring to FIG. 7, the ROM definition consists of the definition of a reference point, the definition of the first array and the definition of the second array. The definition information of the reference point consists of the coordinates and address of the reference point and a bit, the first array definition includes level information ( 0 ), the direction (X direction), the pitch (X_p), the number ( 4 ), the address pitch ( 1 ) and the X-directional array, and the second array definition includes level information ( 1 ), the direction (Y direction), the pitch (Y_p), the number ( 8 ), the address pitch ( 4 ) and the Y-directional array. 
     In the actual layout, the contents of those definitions are used directly or after development. 
     Likewise, a mask option requires an associated address and the position and coordinate information of dummy cells, which are called a mask option definition. Since its correlation table and the like are the same as those for the ROM definition, their description will be omitted. 
     On the premise that the above-described related art is understood, first prior art will be discussed below. FIG. 8 is a block diagram showing the structure of the first prior art, and FIG. 9 is a flowchart for explaining a process sequence according to the first prior art. Referring to FIG. 8, this conventional apparatus comprises a PROM (Programmable ROM) reader  1 , a ROM code input controller  2 , a screen display controller  3 , a display  4 , a data processor  5 , a layout information storage  6 , a keyboard controller  7  and a keyboard  8 . 
     The operation of the first prior art will be described with reference to the block diagram of FIG. 8, the flowchart of FIG. 9, the structural diagram for one bit of a ROM in FIG.  1  and the structural diagram of the pull-up resistor portion of a mask option in FIG.  2 . 
     To begin with, assuming that all the ROM cells are laid out and all the dummy cells of a mask option are laid out, a designer analyzes the design of the circuits to be laid out and the layout pattern. With regard to the ROM section, the arrangement of the X decoder and Y decoder is analyzed for each bit output, and the address of each ROM cell and bit arrangement information are extracted as address signal values (step S 301 ), as shown in FIG.  10 . 
     Next, layout coordinate information is extracted based on the layout coordinates (X, Y) of a reference point  34  (see FIG. 1) as the reference point of one of ROM cells on the layout pattern, and the relative positional relationship among the individual ROM cells, which shows the distance from the reference point  34  computed from a pitch  35  (Y P ) and a pitch  36  (X P ) between ROM cells and the layout number, as shown in FIG. 11, (step S 302 ). For example, information is extracted which indicates that a select signal line Y 1  is selected when A 4  and A 3  in the address signal A 4 -A 0  are 0 and A 2  is 1, and the Y coordinate of the ROM cell selected by this signal line Y 1  is Y+Y P . 
     Subsequently, the designer associates the address bit arrangement information with coordinate information on the layout pattern for each ROM cell to prepare a table indicating bit outputs as shown in FIG. 12, and the table is supplied, together with a size  37  (Y N ) and a size  38  (X S ) of a cell block to be laid out, to the data processor  5  through the keyboard  8  (step S 303 ). 
     With regard to an mask option, likewise, on the assumption that all the dummy cells are laid out, the designer performs the arrangement of the dummy cells of the mask option and extraction of the coordinates by referring to the design of the circuits to be laid out and the layout pattern (step S 301 ′). 
     Further, the extracted cell coordinates are associated with the address bit information of the associated ROM codes to prepare a correlation table (step S 302 ′). This table is supplied, together with information indicating whether layout is carried out when the address associated bit is  0  or  1  and information on the cell block sizes (X m ) and (Y m ), to the data processor  5  through the keyboard  8  (step S 303 ′). 
     The PROM code reader  1  reads a target ROM code (same as “ROM data”) via the ROM code input controller  2  (step S 304 ), and the data processor  5  rearranges the read ROM code in the order of the address bit arrangement information of the individual ROM cells and the dummy cells of the mask option to be associated with one another (step S 305 ). 
     Then, the logic value of the ROM code rearranged in the order of the address bit arrangement information is checked, and when and only when this logic value is “1,” the cell block  33  whose size is designated based on the layout coordinate information of the associated ROM cell is generated as a layout pattern and is stored in the layout information storage  6  (step S 306 ). 
     In this step S 306 , for the mask option, after the logic value of the ROM code is checked, it is determined whether the mask option designates layout for the logic value of “1” or for the logic value of “0.” In the case of layout being made, a cell block whose size is designated based on the layout coordinate information of the associated dummy cell of the mask option is generated as a layout pattern and is stored in the layout information storage  6 . 
     The processing results in step S 306  are displayed on the display  4  for confirmation via the screen display controller  3  (step S 307 ). 
     Next, a layout generating apparatus proposed in Unexamined Japanese Patent Publication No. Hei 5-314215 will be discussed as second prior art. The second prior art is a layout generating apparatus with an improvement made on the ROM layout information generation technique of the first prior art. FIG. 13 shows its structure in a block diagram. FIG. 14 is a flowchart for explaining a process sequence according to the second prior art. 
     Referring to FIG. 13, this second prior art comprises a PROM reader  1 , a ROM code input controller  2 , a screen display controller  3 , a display  4 , a data processor  5 , a layout information storage  6 , a keyboard controller  7 , a keyboard  8 , a ROM position information extractor  9 , a layout inspecting section  12 , and a logic simulation executing section  13 . The operation of the second prior art will be discussed with reference to the block diagram of FIG.  13  and the flowchart of FIG.  14 . 
     First, logic circuit diagram data is read in (step S 401 ). Then, layout pattern data is read (step S 402 ), and test pattern data is read (step S 403 ). Further, a ROM code is read (step S 404 ). 
     Next, the logic simulation executing section  13  prepares the address bit arrangement information of each ROM cell by using the read logic circuit diagram data, test pattern data and ROM code (step S 405 ). 
     Then, the layout inspecting section  12  prepares the coordinate information of each ROM cell by using the logic circuit diagram data and layout pattern (step S 406 ). 
     Then, the ROM position information extractor  9  associates the address bit arrangement information of each ROM cell with the coordinate information (step S 407 ) and the associated address bit arrangement information and coordinate information are rearranged in the order of the address bit arrangement information in association with the ROM code (step S 408 ). 
     When and only when the logic value of the rearranged ROM code is “1,” a cell block with the size designated by a key operation on the keyboard  8  under the control of the keyboard controller  7  is separately output for the associated coordinates, so that the data processor  5  generates a layout pattern which is in turn stored in the layout information storage  6  (step S 409 ). Then, the generated layout pattern is checked (step S 410 ). 
     The second prior art differs from the first prior art in that the second prior art additionally comprises the ROM position information extractor  9 , the layout inspecting section  12  and the logic simulation executing section  13  which are not included in the first prior art. This difference results in such an improvement that address bit arrangement information and coordinate information are automatically generated by the logic simulation and layout inspection. 
     The second prior art, however, has made no improvement on a mask option which has been discussed in the previous section of the first prior art. 
     Now, a mask pattern generating apparatus proposed in Unexamined Japanese Patent Publication No. Hei 6-215069 will be discussed as third prior art. This third prior art is a mask pattern generating apparatus with an improvement made on the ROM layout information generation technique of the first prior art. FIGS. 15 and 16 show the structure of the apparatus in a block diagram. FIG. 17 is a flowchart for explaining a process sequence of the third prior art. FIG. 17 is a flowchart associated with a process of extracting ROM coordinate information and acquiring associated ROM address information, and FIG. 16 is a diagram of a system structure with respect to FIG.  15 . 
     Referring to FIGS. 15 and 16, this third prior art comprises a ROM coordinate extractor  106  for extracting ROM coordinate information from a chip layout data file  105 , a ROM address information reader  107  which receives ROM address information, and a mask pattern generator  109  for generating a mask pattern based on chip layout data  1 , ROM coordinate information extracted by the ROM coordinate extractor  106 , ROM address information and ROM data from a ROM data file  108 . The processing according to the third prior art will be discussed below with reference to the block diagrams of FIGS. 15 and 16 and the flowchart of FIG.  17 . 
     In step S 501 , a CPU  102  receives a layout cell name. Then, the CPU  102  obtains, from chip layout data stored in a storage device  103 , ROM coordinate information which has a layout cell name matching with the one received in step S 501  (step S 502 ). The CPU  102  also receives ROM address information corresponding to the ROM coordinate information (step S 503 ). Then, the CPU  102  determines if the address information is adequate based on a layout cell repeat number included in the ROM coordinate information obtained in step S 502  (step S 504 ). When the address information is checked OK instep S 504 , the CPU  102  proceeds to step S 505  to determine if there is any other layout cell whose address information should be received. When there is no such layout cell found in step S 505 , the entire processing is terminated. 
     A method of automatically extracting address information as a modification of the third prior art (see the second embodiment in the aforementioned Unexamined Japanese Patent Publication No. Hei 6-215069), will now be discussed by referring to the flowchart in FIG.  18 . 
     In step S 601 , the CPU  102  receives the name of a layout cell which constitutes the memory array portion. The CPU  102  extracts ROM coordinate information m the chip layout data based on the layout cell name (step S 602 ). The CPU  102  determines if any other layout cell is present (step S 603 ). When there is a further layout cell in step S 603  (Yes in step S 603 ), the processes in steps S 601  and S 602  are repeated. 
     When there is no further layout cell found in step S 603 , the CPU  102  accepts an input of an address decoder name, extracts the circuit connection information of the decoder portion from the decoder name and chip layout data, and executes logic simulation using the circuit connection information to extract ROM address information (step S 604 ). 
     Finally, the CPU  102  stores the ROM coordinate information and ROM address information in the storage device  103  and then terminates the processing. 
     The third prior art differs from the first prior art in that the third prior art additionally comprises the ROM coordinate extractor  106  and ROM address information reader  107 , which are not included in the first prior art. The additional structure provides such an improvement that ROM coordinate information for an input cell is automatically generated. 
     The processing according to the third prior art, which has been discussed with reference to FIG. 18, has made an improvement in that ROM address information is automatically extracted from the input address decoder name and the chip layout data by performing logic simulation. 
     In the processing system which has been discussed with reference to FIG. 17, the second prior art, address information is input manually as done conventionally, and this third prior art has made no improvement on a mask option which has been discussed in the section of the first prior art. 
     As apparent from the above, the above-described prior arts have the following shortcomings. 
     (1) The first prior art requires a great number of processing steps and significant time and faces a possible occurrence of input errors resulting from manual processing. 
     This is because the first prior art requires that a designer should previously prepare and input arrangement information and coordinate information of ROM cells and arrangement information and coordinate information of a mask option. 
     (2) The second prior art, which is intended to make an improvement on the above problem (1) by using logic simulation and layout inspection, needs that for collation between a layout pattern and logic circuit diagram data, logic circuit diagram data which expresses the whole ROM portions by transistor devices should be prepared at the time of performing layout inspection. This disadvantageously requires a large number of processing steps. 
     More specifically, the ROM portion in a logic circuit diagram is generally described as a functional unit, not by logic symbols and transistor devices or the like. Further, logic simulation is carried out with the ROM portion developed on a memory as an arrangement (matrix) by the number of addresses having a length equivalent to the number of output bits, so that it is necessary to prepare logic circuit diagram data which expresses the ROM portion by transistor devices. Furthermore, logic simulation based on this logic circuit information requires a time, resulting in a considerable number of processing steps and processing time. 
     The second prior art is designed to execute logic simulation and layout inspection on the targeted ROM portion, and is not suitable for extraction of arrangement information and coordinate information of a mask option portion arranged on the whole chip. After all, like the first prior art, the second prior art necessitates extraction of arrangement information and coordinate information through manual processing. 
     (3) Like the first prior art, the third prior art, which additionally comprises the ROM coordinate extractor and ROM address information reader, faces a possible occurrence of input errors or the like caused by manual processing. 
     This is because while the third prior art automatically extracts the coordinate information of the ROM portion, it requires manual inputting of address information. 
     In the modification (second embodiment) of the third prior art which accomplishes automatic extraction of address information, address information is extracted from circuit diagram information and chip layout data. This method, as mentioned above, should execute the process by developing an arrangement (matrix) by the number of addresses having a length equivalent to the number of output bits on a memory and thus requires a considerable time. 
     The conventional method, which extracts address information from circuit diagram information and chip layout data by using logic simulation, extracts only the address and coordinates of the target ROM portion. With regard to the mask option portion, therefore, this method needs manual extraction of arrangement information and coordinate information as per the first prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a layout information generating apparatus and method thereof which extracts the arrangement information and coordinate information of a ROM portion automatically, not manually, to generate a ROM definition, thereby considerably decreasing the number of processing steps to improve productivity. 
     It is another object of this invention to provide a layout information generating apparatus and method thereof which can extract arrangement information and coordinate information even for a mask option portion without using logic simulation, thereby considerably reducing the number of processing steps and processing time to improve productivity. 
     To achieve the aforementioned objects, a layout information generating apparatus according to the first aspect of the present invention comprises first unit for affixing address bit information comprised of text data, as a discriminator, to a typical ROM cell portion indicating a characteristic of an address bit arrangement of a ROM portion of layout data; second unit for reading layout data including the information affixed by the first unit and extracting ROM coordinate information and the text data; and third unit for generating a ROM definition for generating a mask pattern from the extracted ROM coordinate information based on ROM data. 
     A layout information generating apparatus according to the second aspect of the present invention comprises first unit for affixing address bit information comprised of text data, as a discriminator, to a typical ROM cell portion indicating a characteristic of an address bit arrangement of a ROM portion of layout data; second unit for affixing text data, as a discriminator for pattern generation, to all mask option portions of layout data; third unit for reading design information and library information output from an automatic layout tool; fourth unit for reading layout data including information affixed by the first unit and the second unit and extracting ROM coordinate information, mask option coordinate information and the text data; fifth unit for specifying a mask option portion from the cell information read by the third unit and the cell information read by the fourth unit; sixth unit for generating a ROM definition for generating a ROM mask pattern based on ROM data; and seventh unit for generating a mask option definition for generating a mask pattern of a mask option. 
     A layout information generating method according to the third aspect of the present invention comprises the steps of (a) affixing address bit information comprised of text data, as a discriminator, to a typical ROM cell portion indicating a characteristic of an address bit arrangement of a ROM portion of layout data; (b) reading layout data including the information affixed by the step (a) and extracting ROM coordinate information and the text data; and (c) generating a ROM definition for generating a mask pattern from the extracted ROM coordinate information based on ROM data. 
     A layout information generating method according to the fourth aspect of the present invention comprises the steps of (a) affixing address bit information comprised of text data, as a discriminator, to a typical ROM cell portion indicating a characteristic of an address bit arrangement of a ROM portion of layout data; (b) affixing text data, as a discriminator for pattern generation, to all mask option portions of layout data; (c) reading design information and library information output from an automatic layout tool; (d) reading layout data including information affixed by the step (a) and the step (b) and extracting ROM coordinate information, mask option coordinate information and text data; (e) specifying a mask option portion from the cell information read by the step (c) and the cell information read by the step (d); (f) generating a ROM definition for generating a ROM mask pattern based on ROM data; and (g) generating a mask option definition for generating a mask pattern of a mask option. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a one-bit structure for a 32-word ROM; 
     FIG. 2 is a diagram depicting the structure of a mask option for the provision or omission of a pull-up resistor; 
     FIG. 3 is a diagram showing the structure when a dummy cell is laid out; 
     FIG. 4 is a diagram showing the structure when a dummy cell is not laid out; 
     FIG. 5 is a diagram illustrating the correlation between position information and coordinate information of a cell of a 32-word, 1-bit ROM; 
     FIG. 6 is a diagram showing the structure of a 1-bit ROM of 32 words; 
     FIG. 7 is a diagram depicting a compressed ROM definition corresponding to a 32-word, 1-bit ROM; 
     FIG. 8 is a block diagram showing the structure of the first prior art; 
     FIG. 9 is a flowchart illustrating a process flow of the first prior art; 
     FIG. 10 is a diagram showing address bit arrangement information of a ROM cell; 
     FIG. 11 is a diagram showing an address correlation table for individual ROM cells; 
     FIG. 12 is a diagram showing a coordinate correlation table for individual ROM cells; 
     FIG. 13 is a block diagram showing the structure of the second prior art; 
     FIG. 14 is a flowchart illustrating a process flow of the second prior art; 
     FIG. 15 is a block diagram showing the structure of the third prior art; 
     FIG. 16 is a diagram depicting the system structure of the third prior art; 
     FIG. 17 is a flowchart illustrating a process flow of the third prior art; 
     FIG. 18 is a flowchart illustrating a process flow of a modification of the third prior art; 
     FIG. 19 is a block diagram showing the structure of a first embodiment of this invention; 
     FIG. 20 is a flowchart illustrating a process flow of the first embodiment of this invention; 
     FIG. 21 is a diagram exemplarily showing layout data indicating the  0 th bit of a 64-word, 8-bit ROM for explaining the first embodiment of this invention; 
     FIG. 22 is a diagram exemplarily showing layout data to which a text is affixed to define the arrangement of the 0th to third addresses in FIG. 21 for explaining the first embodiment of this invention; 
     FIG. 23 is a diagram exemplarily showing layout data to which a text is affixed to define the arrangement of the 0th to 31st addresses in FIG. 21 for explaining the first embodiment of this invention; 
     FIG. 24 is a diagram exemplarily showing layout data to which a text is affixed to define the arrangement of the 0th to 63rd addresses in FIG. 21 for explaining the first embodiment of this invention; 
     FIG. 25 is a diagram exemplarily showing layout data to which all the text data in FIGS. 21-24 are affixed; 
     FIG. 26 is a diagram exemplarily showing a ROM definition which is acquired from text data affixed in FIG. 22 for explaining the first embodiment of this invention; 
     FIG. 27 is a diagram exemplarily showing a ROM definition which is acquired from text data affixed in FIG. 23 for explaining the first embodiment of this invention; 
     FIG. 28 is a diagram exemplarily showing a ROM definition which is acquired from text data affixed in FIG. 24 for explaining the first embodiment of this invention; 
     FIG. 29 is a diagram exemplarily showing a ROM definition which is acquired from layout data to which all the text data are affixed in FIG. 24 for explaining the first embodiment of this invention; 
     FIG. 30 is a block diagram showing the structure of a second embodiment of this invention; 
     FIG. 31 is a flowchart illustrating a process flow of the second embodiment of this invention; 
     FIG. 32 is an exemplary diagram of layout data including a mask option (provision/omission of a pull-up resistor) for explaining the second embodiment of this invention; 
     FIG. 33 is a diagram exemplarily showing layout data to which text data is affixed to the circuit in FIG. 32 for a mask option for explaining the second embodiment of this invention; and 
     FIG. 34 is a diagram exemplarily showing layout data to which text data is affixed to the circuit in FIG. 32 for a mask option for explaining the second embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. 
     FIG. 19 is a block diagram showing the structure of the first embodiment of this invention. FIG. 20 is a flowchart for explaining the operation of this embodiment. FIGS. 21 through 25 are diagrams exemplarily depicting layout data with text data affixed onto ROM cells. 
     Referring to FIG. 19, this embodiment comprises a PROM reader  1 , a ROM code input controller  2 , a screen display controller  3 , a display  4 , a data processor  5 , a layout information storage  6 , a keyboard controller  7 , a keyboard  8 , a layout data analyzer  10  and a ROM definition generator  11 . 
     Referring to FIG. 20, first, a designer reads basic layout data and affixes text data as a discriminator to characteristic ROM cells with respect to the address arrangement of a ROM portion (step S 101 ). As the designer is actually carrying out the layout of the ROM, it is unnecessary to analyze the addresses. 
     A method of affixing text data in step S 101  will be described below specifically with reference to FIGS. 21-25. 
     FIG. 21 shows a part of layout data showing the arrangement of ROM cells at the 0th bit in n bits×64 words. In FIG. 21, numerals in blocks or symbols indicating ROM cells indicate addresses corresponding to the respective ROM cells. 
     Referring to FIG. 21, addresses  0  to  31  are arranged four across and eight sets each of four addresses vertically in the ascending order at the same pitches, and addresses  32  to  63  are arranged like the addresses  0 - 31  in the mentioned arrangement shifted rightward. At this time, the designer affixes text data in the following manner. 
     To define four repeats of addresses  0 - 3  in the X direction, the repeat level and the number of repeats are affixed as text data to the ROM cell which becomes a reference of the 0th address. Further, text data is affixed to the second ROM cell (first address) in repetition as a mark for pitch computation. FIG. 22 exemplarily shows how the text data is affixed. Referring to FIG. 22, text data indicative of information of “level 1, first cell, four repeats” is affixed to the ROM cell at the 0th address, and text data indicative of information of “level 1, second cell” is affixed to the ROM cell at the first address. 
     To define eight repeats of addresses  0 - 31  in the Y direction at a pitch of four addresses, as in the previous case, the repeat level and the number of repeats are affixed as text data to the ROM cell at the 0th address. Further, text data is affixed to the second ROM cell (fourth address) in repetition. FIG. 23 exemplarily shows how the text data is affixed. Referring to FIG. 23, text data indicative of information of “level 2, first cell, eight repeats” is affixed to the ROM cell at the 0th address, and text data indicative of information of “level 2, second cell” is affixed to the ROM cell at the fourth address. 
     To define two repeats of addresses  0 - 63  in the X direction at a pitch of thirty-two addresses, as in the previous case, the repeat level and the number of repeats are affixed as text data to the ROM cell at the 0th address. Further, text data is affixed to the second ROM cell (32nd address) in repetition. FIG. 24 exemplarily shows how the text data is affixed. Referring to FIG. 24, text data indicative of information of “level 3, first cell, two repeats” is affixed to the ROM cell at the 0th address, and text data indicative of information of “level 3, second cell” is affixed to the ROM cell at the 32nd address. 
     When affixing of text data necessary to define entire the arrangement is completed, affixing of text data is completed. 
     FIG. 25 shows all text data affixed to the layout data shown in FIG.  21 . 
     Text data is affixed in the above manner in such a way that the arrangement of the addresses of all the ROM portions can be determined. 
     Referring again to the flowchart in FIG. 21, the screen display controller  3  then reads layout pattern data affixed with text data in step S 101  (step S 102 ). Text data affixed to a ROM portion in the read layout pattern data is extracted (step S 103 ). 
     Further, coordinate information of a ROM cell to which text data is affixed is extracted (step S 104 ). 
     Using the read text data and the coordinate information extracted in step S 104 , a ROM definition is prepared (step S 105 ). A detailed description will now be given of how a ROM definition is generated from a sequence of text data, exemplarily shown in, for example, FIG. 25, in step S 105 . 
     First, text data is extracted from the one of a lower repeat level. More specifically, text data of the first level is extracted. That is, the text data affixed in FIG. 24 is extracted, the size of a block of the first ROM cell is acquired from that cell, and the pitch between cells is automatically computed from the coordinates (base coordinates) of the first cell and the coordinate information of the second cell. 
     Through the above-described process, a ROM definition as shown in FIG. 26 is generated. (Note that the definition of the block sizes of ROM cells is prepared separately as a common one to individual ROM definitions.) Referring to FIG. 26, with regard to the arrangement (array) with the base coordinates (Xg, Yg), the address bit ( 0 ,  0 ) and level  1 , definition information specifying the direction as the X direction, the pitch of Xp 1 , the repeat number of 4 and the address pitch of  1  is generated. 
     Likewise, as regards the second level, the pitch and address pitch are computed from the text data affixed in FIG.  23 . Through this process, a ROM definition as shown in FIG. 27 is generated. Referring to FIG. 27, with regard to the arrangement with level  2 , definition information specifying the direction as the Y direction, the pitch of Yp 1 , the repeat number of  8  and the address pitch of  4  is generated. 
     Likewise, as regards the third level, a ROM definition as shown in FIG. 28 is generated. Referring to FIG. 28, with regard to the arrangement with level  3 , definition information specifying the direction as the X direction, the pitch of Xp 2 , the repeat number of  2  and the address pitch of  32  is generated. 
     In step S 105 , as a ROM definition corresponding to layout data which shows the arrangement of the ROM at the 0th bit in n bits×64 words shown in FIG. 21, a ROM definition shown in FIG. 29 is generated as definition information which is a combination of ROM definitions shown in FIGS. 26-28. 
     Referring again to FIG. 30, then, the PROM code reader  1  reads a ROM code via the ROM code input controller  2  (step S 106 ). In accordance with the read ROM code, the designated block is laid out and is stored in the layout information storage  6  (step S 107 ). 
     Then, the prepared layout pattern is displayed on the display  4  for the confirmation of this layout pattern under the control of the screen display controller  3  (step S 108 ). 
     The second embodiment of this invention will now be discussed. FIG. 30 is a block diagram showing the structure of the second embodiment of this invention. FIG. 31 is a flowchart for explaining the operation of this embodiment. 
     Referring to FIG. 30, this embodiment comprises a PROM reader  1 , a ROM code input controller  2 , a screen display controller  3 , a display  4 , a data processor  5 , a layout information storage  6 , a keyboard controller  7 , a keyboard  8 , a layout data analyzer  10 , a design information analyzer  14 , a ROM definition generator  11  and a mask option definition generator  15 . 
     Referring to FIG. 31, first, a designer reads basic layout data and affixes text data as a discriminator to characteristic ROM cells with respect to the address arrangement of a ROM portion (step S 201 ). As this step S 201  is the same as the step S 101  in the first embodiment which has already been described with reference to FIG. 20, its description will be omitted. 
     Next, the designer reads basic layout data and affixes necessary information, such as the type of a mask option and the address of associated input ROM data, to a dummy cell in the mask option portion in the layout data as text data (step S 202 ). 
     A description will now be given of how to affix text data with reference to FIGS. 32,  33  and  34 . Of those figures, FIG. 32 shows a part of actual layout data and an example where there is a mask option (existence/non-existence of a pull-up resistor). 
     The designer affixes the type of the mask option, the associated ROM data address and the layout layer of the cell as text data to this dummy cell. FIG. 33 shows how text data is affixed to the dummy cell. Referring to FIG. 33, information of “pull-up resistor, associated ROM address, layout layer name” is affixed as text data to a dummy cell  22 . 
     Referring again to FIG. 31, then, the data processor  5  reads design information and library information, output from an automatic layout tool, and extracts all cell information present on the layout (step S 203 ). 
     Next, the data processor  5  reads layout pattern data with text data affixed in steps S 201  and S 202  (step  5204 ). 
     Then, the text data affixed to the mask option portion is extracted first from the read layout data (step S 205 ). 
     Further, cell information in the mask option portion is extracted (step S 206 ), and is collated with the cell information extracted in steps  5203  and  5206  to specify the mask option portion (step S 207 ). 
     The text data extracted in step S 205  is analyzed (step S 208 ) to generate a mask option definition (step S 209 ). FIG.  34  shows the mask option definition generated in step S 209 . 
     Further, a process of generating a ROM definition for the ROM portion or a process sequence from step S 210  to step S 212  is executed. Because this process is the same as the process from step S 103  to step S 105  in the first embodiment, its description will be omitted. 
     When the ROM definition and mask option definition are completed, the block of the ROM cell and the block of the mask option are laid out in accordance with the contents of the input ROM code (step S 213 ). Finally, the generated layout pattern is checked (step S 214 ) after which the processing will be terminated. 
     As apparent from the above, this invention has the following advantages. 
     (1) The first advantage of this invention can significantly reduce the number of processing steps and processing time required for extraction of arrangement information and coordinate information as compared with the manual extraction done in the prior arts, and can prevent errors originated from a manual work. 
     This is because in this invention, a discriminator is affixed as text information to a ROM portion and a mask option portion so that a ROM definition as arrangement information and coordinate information of each ROM cell and a mask option definition as arrangement information and coordinate information of a dummy cell in a mask option are automatically extracted. 
     (2) To quantitatively explain a specific advantage of this invention, it takes about two weeks by a manual work to check arrangement information and coordinate information of a ROM portion from layout data, compute a pitch and generate a ROM definition and a mask option definition, whereas this invention, it is expected, completes all the processes including inspection in about two days. 
     (3) Another advantage of this invention eliminates the need for logic simulation which has been employed conventionally, making it possible to eliminate the preparation steps and time corresponding to the execution of logic simulation and provide an apparatus which provides a high design quality without performing this logic simulation. 
     (4) A further advantage of this invention eliminates the need for manual extraction of arrangement information and coordinate information for a mask option, thereby ensuring reduction in a significant number of steps and considerable time. This can further reduce man-made errors. 
     This is achieved by the structure of this invention to automatically generate a mask option definition as a layout definition of a dummy cell associated with a mask option.