JPS6356547B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to read-only memories, and more particularly to read-only memories for storing character fonts.

[Background of the invention]

Character font is m ₁ × m ₂ (m ₁ m ₂ is a positive integer)
Characters are represented by assigning white or black to each element of the matrix. Figure 1 is an example of a character font consisting of 10 x 10 elements, representing the kanji 〓Rock〓.

The storage capacity of the read-only memory that stores character fonts is 16 x 16 for the font size and 16 x 16 for the number of characters.
3000, approximately 770K bits are required, and if the font size is 32 x 32 and the number of characters is 4000, approximately 770K bits are required.
4M bits are required. With current semiconductor technology, it is difficult to store desired values in all storage elements in a large-capacity read-only memory due to manufacturing technology. Therefore, error correction and
Since correction is necessary, various error correction/correction methods have been considered. A method using an error correction code such as a Hamming code has a high degree of redundancy and requires a relatively large-scale error correction circuit, which is not necessarily a good idea in terms of economy and reliability. In addition, a simple odd-even test has only a detection ability but not a correction ability and lacks a correction ability. There is also a method of preparing multiple identical read-only memos and reading out the contents of another read-only memory if an error is detected by an odd-even test, but this is economically difficult due to the large degree of redundancy.

[Purpose of the invention]

The purpose of the invention is to not require large redundancy;
The object of the present invention is to realize a read-only memory having a circuit for correcting storage errors in a character font read-only memory section with a relatively small-scale circuit.

[Summary of the invention]

In order to achieve the above object, the present invention includes a circuit that performs error correction using characteristics specific to character fonts. First, the characteristics peculiar to the above-mentioned character font will be explained using an example. Figure 2 represents a character font of size 10 x 10. In this character font,
Attention is paid to a plate 1 having a size of 3×3 as shown by the broken line in FIG. This plate can occupy eight different locations in the row and column directions, so a total of 64 locations can be considered. Also, since the plate is 3x3 in size, it has 9 elements, each of which is either white or black, so 2 ⁹ =
512 patterns (e.g. all white, all black, checkered)
is possible. However, due to the nature of character fonts, there are patterns that are easy to appear and patterns that are difficult to appear. This is a characteristic unique to character fonts. In the case of a character font of size 10×10, patterns a and b in FIG. 3 are very difficult to appear, and patterns a' and b' are relatively easy to appear. Therefore, in the present invention, if an error is detected in the example contents of the i-th address of the read-only memory, the contents of the (i-l)-th and (i+)-th
1) Using the contents of the address example, examine the 3x3 plate above, and if there is a pattern in Figure 3 a, go to a'.
If there is a pattern b, modify it to b'. If an error is detected and neither pattern a nor b is included, or if the i-th address is in the top or bottom line of the character font, it may be determined that correction is not possible.

Figure 3 is an example, and the size of the character font,
The frequency of plate pattern appearance varies depending on the size of the plate.

[Embodiments of the invention]

FIG. 4 shows an embodiment according to the invention. In this embodiment, the size of the character font is 10×10.
In FIG. 4, address generator 2 indicates the address of a line of character fonts. Read-only storage section 3
The length of each word (corresponding to a row of character fonts) is 11 bits, with 1 bit being the parity check bit. Since one character font consists of 10 lines, a storage capacity equal to the total number of characters x 10 x 11 bits is required. The odd-even check circuit 4 is a circuit that performs an odd-even check on each word read from the read-only storage section 3, and if no error is detected, outputs the word to the outside through the output line 5. If an error is detected, it is transferred to the pattern matching circuit 6. The pattern matching circuit has a memory 7 that stores the word in which an error has been detected and the words before and after it, and checks to see if there is one among the 64 3×3 plates that matches the pattern indicated by 1'. It is a circuit. If there is a match, the pattern matching circuit 8 corrects the pattern shown by 1'' in FIG. 4 and outputs it to the outside through lines 9 and 5. If a plate that matches cannot be detected, it is determined that it cannot be modified, and the output is output through 10 and 5 to the outside.

In this example, the size of the character font is set to 10×10
Although the size of the plate has been described as 3×3, it is not limited to this, and the modification pattern of the plate is not limited to the example shown in FIG.

As described above, the present invention can be applied to a character font having a size of 10 x 10, for example, in which the patterns a and b in Fig. 3 are difficult to appear, and the patterns a' and b' in Fig. 3 are likely to appear. This property is used to correct memory errors in the read-only storage unit.

〔Effect of the invention〕

Using a read-only memory according to the present invention, a read-only memory having circuitry for correcting storage errors in a character font read-only memory can be implemented with relatively small circuitry without requiring large redundancies.

[Brief explanation of drawings]

Figure 1 shows an example of a character font, Figure 2 shows an example of a character font and plate, and Figure 3 shows an example of a character font and plate.
The figure shows an example of a plate pattern, and FIG. 4 shows an embodiment of a read-only memory according to the present invention. 1...Plate, 2...Address generator, 3...
...Read-only storage section, 4...Odd-even test review, 6
...Pattern matching circuit, 7...Memory, 8
...Repair circuit.

Claims (1)

[Claims] 1 Each word is n bits long (n is an integer greater than or equal to 2)
It is a read-only memory that uses one bit out of the n bits of each word as an odd-even check bit and performs an odd-even check when reading, and this check detects an error in the word at address i. In this case, from the (i-j)th address to the (i+k)th address
1. A read-only memory comprising: a circuit for modifying information at an i-th address using information stored at an address (j, k are integers).