Character generator

Abstract

A character generator for a raster scanned display includes a virtual memory, a character memory, and character memory addressing circuitry. Character identifying codes are received by the virtual memory which produces the addresses in the character memory for the data for the first scanned line of each character. The character data for each scanned data line of a character contains sequential words containing N bits of video data to be displayed and two link bits. The link bits apprise the character memory addressing circuitry if subsequent words for that character appear on that scanned data line and if additional data lines for that character will have to be read on subsequent scans of the raster display frame.

Claims

I claim:

1. A character generator for receiving input character data and generating corresponding characters of variable size and shape in the form of dot matrices on a raster scan display, comprising:

a character memory for storing information defining a characteristic dot matrix for each distinguishable character, said information including a plurality of dot matrix data fields, each field having a plurality of link bits associated therewith for defining the position of the field within the dot matrix of a character.

2. The character generator of claim 1 further comprising:

a virtual memory for receiving said input character data and generating for each distinguishable character a corresponding stored character memory address adapted to define a location in the character memory having the associated dot matrix information for said distinguishable character.

3. A character generator for receiving input character data and generating corresponding characters of variable size and shape in the form of dot matrices on a raster scan display, comprising:

a character memory for storing information defining a characteristic dot matrix for each distinguishable character, said information including a plurality of dot matrix data fields, each field having a plurality of link bits associated therewith for defining the position to the field within the dot matrix of a character; and

a virtual memory for receiving said input character data and generating for each distinguishable character a corresponding stored character memory address adapted to define a location in the character memory having the associated dot matrix information for said distinguishable character.

4. A character generator for receiving input character data and generating corresponding characters of variable size and shape in the form of dot matrices on a raster scan display, comprising:

a character memory for storing information defining a characteristic dot matrix for each distinguishable character, said information including a plurality of dot matrix data fields, each field having a plurality of link bits associated therewith for defining the position of the field within the dot matrix of a character, said link bits being adapted to identify the last field of a character on a scan line and to identify the last field of the dot matrix of a character.

5. The character generator of claim 4 further comprising:

a virtual memory for receiving said input character data and generating for each distinguishable character a corresponding stored character memory address adapted to define a location in the character memory having the associated dot matrix information for said distinguishable character.

Description

The present invention relates to a character generator for generating characters in the form of dot matrices in dependence on supplied character information, said generator comprising a character memory in which for each character there is stored information which constitutes the dot matrix of the character.

Character generators of the above kind are known before, and such a generator is schematically shown in FIG. 1a in its context. An information source 1 delivers information about the characters to be presented by means of a presentation member 4. The information source may be a computer or a keyboard, and the presentation member 4, for example, a cathode ray tube or a typewriter. In the following the presentation member is assumed to be a cathode ray tube. The source 1 supplies for each character to be presented a character code TK in the form of a binary word to the regenerative memory 2, where the word is stored. A large number of such words (= characters) may be stored simultaneously in the memory. For each character to be written the memory 2 delivers a word constituting the character code TK of the character to the character generator 3. The character generator consists, in principle, of a memory in which a dot matrix is stored for each character, said dot matrix containing information as to which dots are to be lighted or extinguished in the form of, for example, a number of consecutive bits. FIG. 1b shows a simplified example of how the character shown in the figure is built up of a dot matrix with three raster lines I, II and III, each having three dots. If a lighted dot on the cathode ray tube is designated with a binary one and an extinguished dot with a zero and if the dots are assumed to be taken in numerical order, the word which constitutes or contains the dot matrix of the character will be as follows:

010 111 010

The character code supplied from the regenerative memory 2 acts as the address for the place in the memory in the character generator where the dot matrix of the character is stored. When a certain character code is delivered from the regenerative memory 2, the character generator 3 thus delivers a word PM, constituting the dot matrix of the character, to the presentation member 4 (the cathode ray tube), and this word then controls the intensity of the electron beam so that (see the above example and FIG. 1b) the character is displayed on the cathode ray tube.

After each character, a signal a is delivered from the character memory 3 or the presentation member 4 to the regenerative memory 2, which then delivers the code for the next character to the character memory. As long as no changed information is received from the source 1, all the characters that are presented on the cathode ray tube at the time are stored in the regenerative memory, and all these characters are written out periodically on the cathode ray tube, for example 50 times per second.

Systems of this kind involve the disadvantage that all the dot matrices must have equal heights and widths, that is constant line spacing and constant character spacing must be employed. Further, in each matrix all the dots of the matrix must be run through each time even if only a small number of them are used for the character. This results in great demands on the memory capacity, a low working speed, and, if several character sizes are desired, a complete set of memories for each character size must be arranged. If it is desirable to have more than two character sizes the character generator will therefore become prohibitively expensive, since the very memory capacity is an extremely costly part of this kind of equipment.

The invention aims to provide a character generator, in which it will be possible with a reasonable memory capacity to present characters in the form of dot matrices of arbitrary size, and the size of the characters/the matrices may vary arbitrarily from character to character both in height and in width. A device according to the invention further makes it possible, particularly for complicated characters, to use dot matrices of other shapes than rectangular, which may result in a considerable reduction of the required memory capacity and an increase in speed.

What characterises a character generator according to the invention will be clear from the appended claims.

The invention will be described in greater detail with reference to the accompanying FIGS. 1-7.

FIG. 1a shows a block diagram for a previously known character generator and FIG. 1b an example of a character generated by such a generator.

FIG. 2 shows the principle of a character generator according to the invention.

FIG. 3a shows in more detail an example of the operation and construction of such a character generator, and FIG. 3b an example of the appearance of the characters that are stored in the generator according to FIG. 3a.

FIG. 4 finally shows examples of further characters which may be generated with the help of a generator according to the invention.

FIG. 5 shows in more detail a device according to the invention,

FIG. 6 shows a word in the character memory and the corresponding dot matrix.

FIG. 7 shows an example of a character with its word in the character memory.

FIGS. 1a and 1b have been described above. FIG. 2 shows how a character generator 3 according to the invention is divided into a so-called virtual memory 5 and a character memory 6. The incoming character code TK is supplied to the virtual memory 5. This is a highly real memory and in it there is stored for each character code the address of the location in the character memory 6 where the dot matrix for the corresponding character is stored. Thus, if the character code (TK) for, for example, the letter "A" comes in from the regenerative memory 2, the memory 5 picks out and delivers to the character memory 6 the address (ADR) of the location in the memory 6 where the dot matrix for the letter A is stored, and this dot matrix is then delivered in the form of a digital word (PM) to the presentation member. Seen from the input side of the character generator, the virtual memory 5 has the same function as the known character generator (3 in FIG. 1), where the character code selects the dot matrix of a character directly in the character memory. Since, therefore, the memory 5 from this point of view can be regarded as a character memory despite the fact that it is not, it is referred to here as a "virtual memory".

FIG. 3a shows in more detail an example of the construction and function of the character generator according to the invention. The virtual memory 5 contains K-2 cells, one for each character, and in each cell there is a word constituting the address of the cell in the character memory 6 in which the first field in the dot matrix of the character is stored. The character memory 6 contains a number of K cells with the addresses 1, 2, 3 . . . K-1, K, and each cell contains a field in the dot matrix of a character, as well as a number of link bits.

The concept "field" refers to a subordinate unit in the dot matrix of a character. In the case described here, a field is three consecutive dots in the matrix, that is, the so-called field size is three bits. FIG. 3b illustrates the concept. Character No. 1 there consists of fields 1-12, which are run through in sequence. In the example, field 1, for example, consists of bits 000, field 2 of bits 010, field 3 of bits 000, and so on. However, the field size may be selected arbitrarily and has therefore been designated N in FIG. 3a. Each field thus corresponds to and gives rise to N dots after each other in the direction of the raster lines on the cathode ray tube.

The link information in each cell in the character memory consists in the example of two bits with the following significance:

    ______________________________________
    binary code
                 significance
    ______________________________________
    00         First field in the dot matrix. Next
               field is in the subsequent physical
               address.
    01         The next field is in the subsequent
               physical address.
    10         The last field on this raster line.
               The next field present in the subsequent
               physical address. If each raster line
               consists of only one dot, 10 may also
               indicate the first field in the dot ma-
               trix.
    11         The last field in the dot matrix.
    ______________________________________

• Inventors
  Lundstrom, Jan-Erik;
• Assignee
  ASEA Aktiebolag (Vasteras, SE)
• Published
  Dec-26-1978
• Current US Classes:
  345/469
  715/529
• Application #
  759208
• International Classes
  G06K 015/20
• Field of Search
  340/324 364/521
• Examiner
  Trafton; David L.
• Agent
  Pollock, Vande Sande & Priddy
• US Patent References:
  3952297