JPS6145500A - Read-only memory of character font - Google Patents

Abstract

PURPOSE:To correct misstorage in a ROM by forming a circuit for executing error correction using the specific property of a character font. CONSTITUTION:An address generator 2 specifies the address of a line in a character font. An odd/even testing circuit 4 executes the even/off test of each word read out from the ROM 3, and if an error is detected, transmits the data to a pattern matching circuit 6. The circuit 6 has a memory 7 for storing the word detected at its error and the words arrayed before and after the word concerned, checks the existence of a pattern matched with a pattern indicated by 1' out of sixty-four 3X3 plates, and if a coincident patter exists, the pattern is corrected by the pattern indicated by ''1'' in a correcting circuit 8 to output the corrected pattern. When no coincident pattern is detected, the pattern is decided as an incorrectable one and the status is outputted.

Description

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

[Background of the invention]

A character font represents characters by assigning white or black to each element in m1×m2 (m1m2 is a positive integer) rows. FIG. 1 is an example of a character font having a size IOX of 105 elements, and represents the kanji ``rock''. ' The storage capacity of the memory dedicated to the memory of character fonts is 16 x 16 for the font size and 3000 for the number of characters.
If this is the case, approximately 770 bits will be required, and if the font size is 32×32 and the number of characters is 4000, approximately 4 Mbits will be required. With the current semi-integrated technology, it is difficult from a manufacturing technology standpoint to store a desired value in every storage element in a large-capacity read-only memory. Therefore, there is a need for error correction/modification at the time of reading, and various error correction/modification methods have been considered. Methods using error correction codes such as Hamming codes have a high degree of redundancy and are relatively large-scale. This method requires an error correction circuit, which is not necessarily a good idea in terms of economy and reliability.Furthermore, a simple odd-even test has only detection ability but no correction ability, and lacks correction ability.

If you prepare multiple copies of the same read-only memo and find an error in the odd-even test.

There is also a method of reading the contents of another memory only for entertainment, but this method requires a large degree of redundancy and is economically difficult. [Objective of the Invention] The purpose of the present invention is to The object of the present invention is to realize a read-only memory having a circuit for correcting a memory error in a read-only memory section for character fonts with a circuit of this size.

[Summary of the invention]

In order to achieve the above object, the present invention has a circuit that performs error correction using characteristics specific to character fonts.First, the characteristics of the character 7 on If present will be explained using an example. Represents a character font of size l0XIO.

In this character font, attention is paid to the plate 1 having a size of 3×3 as shown by the broken line in FIG. This plate occupies eight different locations in the row and column directions, so a total of 64 locations can be considered. Also, since the plate is of size b53 x 3, it itself has 9 elements, each of which is either white or black, so 2'
-512 patterns (for example, all days, all points, checkered pattern) are possible. However, due to the nature of character fonts, there are some patterns that are easy to appear and others that are difficult to appear. This is a characteristic unique to character fonts. Size l0XIO
In the case of the character font in Figure 3 (a), (bl is a pattern that is very difficult to appear (al', (b)
' is a pattern that appears relatively easily.

Therefore, in the present invention, when an error is detected in the example contents of the first address of the read-only memory,
i + 1) Using the contents of the example of i place, examine the above 3 x 3 plate, and if pattern 2>5 of (al) is found in Figure 3 (al
', (If there is a b pattern, modify it to (b)').If an error is detected and neither a nor b pattern is included, or if the first address is the bottom line of the character font, If it is the bottom line, it may be determined that it cannot be modified.

The third factor is just one example; the frequency of plate pattern appearance differs depending on the size of a single character font and 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 10XIO. In FIG. 4, the address generator 2 indicates the line address of the character font. The length of each word (corresponding to a line of the character font) in the read-only storage 3 is 11 bits, one bit being an odd-even check bit. One character font is 10
Since it consists of 1 line, the total number of characters x 10
A storage capacity of 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 for storing the word in which an error has been detected and the words before and after it, and checks whether there is one among the 3×3 plates 64 that matches the pattern indicated by 1'. It is a circuit.

If there is a match, it is modified by the modification circuit 8 into the pattern indicated by 1'' in FIG. 4, and output to the outside through lines 9 and 5. Pattern matching circuit 61) 1
1. , ' When a plate matching the pattern indicated by ' is not detected, it is determined that the plate cannot be modified, and the process follows step 10.5 and is output to the outside.

In this embodiment, the character font size is 10×10 and the plate size is 3×3. However, the present invention is not limited to this, and the modification pattern of the plate is not limited to the example shown in FIG. 3. .

As described above, the present invention is advantageous in that, for example, in a character font having a size of 10XIO, the patterns of (al, (bl) in FIG. 3(a)', (b)',
The purpose is to correct memory errors in the C-extrusion-only storage unit by utilizing the characteristics peculiar to character fonts, such as the tendency for patterns to appear easily.

〔Effect of the invention〕

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

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a character font, FIG. 2 is a diagram showing an example of a character font and plate, FIG. 3 is a diagram showing an example of a plate pattern, and FIG. 4 is a diagram showing an example of a read-only memory according to the present invention. It is a figure showing an example. 1...Plate, 2...Address generator, 3id
4. Odd-even test, 6. Pattern matching circuit, 7. Memory, 8. Modification circuit. '￥J 1 times 2 Figures (0,, N (and 1.')
(bn (b′)′!J 4 Close■

Claims (1)

[Claims] 1. A read-only memory in which each word is n bits long (n is an integer of 2 or more), and one bit out of the n bits of each word is assigned as an odd-even check bit, and an odd-even check is performed when reading. circuit, and if an error is detected in the word at the i-th address by this inspection, the information stored at the (i-j)-th address to the (i+k)-th address (j, k are integers) is used to update the word at the i-th address. A read-only memory comprising a circuit for modifying information.