JP2872808B2 - High-speed character generator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to all-point addressable printers, and more particularly to bitmap character generators for generating print signals that are supplied to a marking engine in such printers. Involved.

BACKGROUND OF THE INVENTION U.S. Pat. No. 4,079,458 issued Mar. 14, 1978 to Rider et al. Discloses a bitmap character in which a character bitmap is stored in reduced form to save storage space in a character font storage device. A generator is disclosed.
FIGS. 2 and 3 show typical bitmaps of the letter "A" in standard portrait and standard landscape modes, respectively. The traditional M (full-width) square storage format is indicated by a solid line 10 as compared to the reduced storage format indicated by a dashed line 12 in the format described in the patent to Ryder.
Each bit in the character is represented in the storage device as a 1 and each bit outside the character within the rectangular boundaries of the character is represented as a 0. As can be seen in FIGS. 2 and 3, the storage requirements for characters can be significantly reduced by eliminating surrounding areas such as consisting only of zeros. However, when reducing the format in this manner, certain types of characters, such as the character baseline, the spacing between characters, and the number of words (a word is a group of 16 bits) in a bitmap character representation, are used. Information is lost. It is necessary to provide this information for bitmap character generators that use reduced fonts. FIG. 4 is a simplified block diagram of a prior art character generator of the type shown in U.S. Pat. No. 4,079,458 using a reduced format bitmap font. The character generator includes a main processing unit 20 that receives a print command from an input device (not shown) such as a personal computer. Main memory 20 typically comprises a programmable microprocessor. Lookup table 22 contains font parameters such as character height, width, and font address, as well as character alignment (Δx,
Δy). Δx, Δ
y defines an array in the lower left corner of the reduced form bitmap relative to the reference line location where the character should be placed. Main processor 20 retrieves character parameters and statistics from lookup table 22 by addressing the lookup table with a character identifier (ID) such as an ASCII code. Main memory 20 calculates the x, y page position for the character using the character statistics and sends the character height, width, font address, and x, y page position to pit map character generator 24. The bitmap character generator 24 retrieves the character bitmap from the font storage 26 using the font address and the height and width of the character, sends the bitmap to the buffer 27, and from there the marking engine (shown). It has not been)
Send to The buffer 27 can consist of a line or page buffer, depending on the design of the character generator.

Since main processor 20 is a programmable microprocessor, each font parameter search takes a different order of machine instructions, but this consumes processor time and limits the rate of character generation, and therefore It is an object of the present invention to provide an improved character generator of the type using reduced fonts.

SUMMARY OF THE INVENTION This object is achieved according to the present invention by providing a storage device containing width, height and font address data for each character to be generated by a character generator. The constant speed call store is addressed by the main processor with a character identifier code, and in response provides direct character width, height and font address information to the bitmap character generator, thereby increasing the overall rate of character generation. Increase.

In the preferred embodiment of the present invention, separate constant speed call storages are provided for width, height, and font address data, which are addressed in parallel with character identifiers. The font storage associated with the bitmap character generator contains a plurality of fonts, and the font address information is obtained by combining a font selection code with a standard character code such as ASCII to provide an address to be added to the constant speed call storage. Is generated by generating a composite character identifier. Since the constant speed call store is dual ported, its contents can be modified by the main processor to accommodate the new font.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram illustrating a bitmap character generator according to the present invention; FIG. 2 is a diagram illustrating a conventional em (full) square font in a standard portrait mode with reduced fonts used by the present invention; FIG. 3 is a diagram comparing a traditional M square font with a reduced font in landscape mode, and FIG. 4 is a schematic diagram illustrating a bitmap character generator representative of the prior art. FIG. 5 is a schematic diagram illustrating an apparatus for switching between font modes in accordance with the present invention.

Referring to FIG. 1, a character generator according to the present invention is shown, wherein elements similar to those in FIG. 4 are similarly numbered. The look-up table 22 associated with the main processor 20 includes font statistics Δx, which are used to calculate the x, y position at which the reduced storage bitmap is to be printed and sent to the bitmap character generator 24. Δ
It contains only y and character spacing. The x, y character positions are calculated by main processor 20 as follows.

x = X + Δx and y = Y + Δy where X is the position for each character along the pixelated line, and each new X is calculated from the preceding X. In the portrait configuration, X _new = X _before + character spacing, Y is the position of the reference line of each character represented by a pixel, and the desired spacing between lines (for example, single,
And half, double, etc.). In other configurations, X and Y increment separately since they are referenced to the paper.

The font parameters required by the bitmap character generator 24 are the character width W (in bits),
Character height (H, in bits) and font storage 26
Provided by constant speed paging storage (RAM) 28, 30, and 32 containing the character start address (FA) at RAMs 28, 30 and 32 are simultaneously addressed by main processor 20 with a character identifier (ID). The outputs of RAMs 28, 30 and 32 are provided directly to bitmap character generator 24, along with the x, y character position information calculated as described above.

Upon receiving the font parameters, bitmap character generator 24 looks up the first word of the character stored in font storage 26 at location FA and sends this word to location x, y in page storage. .

Next, the bitmap character generator 24 retrieves the word of the character at font store location FA + 1 and sends it to page store location x + 16, y. In this manner, the bitmap character generator continues to send bitmap words from font storage location FA + N to page storage location x + 16N, y, up to N = H character heights. If the width W of a character is only one line, the character generation is complete.
If the width W is greater than one, the bitmap character generator sends the next word at location FA + H + 1 in bitmap storage to location x + 1, y in page storage. FA + W +
The next word in 2 is sent to x + 1, y + 16, and so on, eventually sending the word in the second column of the bitmap. Bitmap character generator 24 continues in this manner until the entire character has been sent to page storage.
Main processor 20 then stores the next character ID in parameter RAM 28,
Send to 30 and 32 to generate the next character in the image.

In the preferred embodiment of the present invention, several character fonts are stored in font storage 26. The font identifier is combined with the character identifier, and the combination identifier is the width, height and font address RAMs 28, 30 and 32.
Is added to For example, if the 7-bit ASCII character identifier is 6
Combined with the bit font identifier, a 13 bit ID is added to the RAM. Because font identifiers are relatively rarely changed relative to character identifiers, font identifiers are generated once by main processor 20 and stored in latches until changed. Provision has also been made for switching between 7-bit ASCII character identifiers commonly used in the United States and 8-bit extended ASCII character identifiers commonly used in Europe. In the case of an 8-bit ASCII character identifier, only 5 bits are used for the font identifier code.

FIG. 5 is a schematic diagram illustrating an apparatus for latching a font identifier and switching between a 7-bit ASCII mode and an 8-bit ASCII mode. An 8-bit character identifier is provided from main processor 20 to bit combiner 42 via line 40. In 8-bit extended ASCII mode, all 8
Bits are used. In 7-bit ASCII mode, only the first 7 bits are used. A 6-bit font identifier is provided to latch 46 via line 44. All 6 bits of the font identifier can be used with a 7-bit ASCII code, but only 5 bits of the font identifier are used with an 8-bit extended ASCII code. The mode switch 48 controlled by the main processor 20 is switchable between the eighth bit of the character identifier code and the sixth bit of the font identifier code. This mode switch is used to select the appropriate character and font identifier bits depending on the type of font stored in font storage 26.

In the preferred method of practicing the present invention, the new fonts can be easily loaded into the storage because the RAMs 28, 30 and 32 and the font storage 26 are dual ported.

Although the description of the font bitmap and the definition of the x, y page positions have been described for portrait mode, the invention is equally valid for other character configurations, such as landscape mode.

INDUSTRIAL APPLICABILITY AND ADVANTAGES The character generator according to the present invention is useful in all point addressable printers and is advantageous because characters can be easily generated for higher printing speeds.

Claims (5)

(57) [Claims] 1. A device for generating a bitmap representation of information to be printed by a point-addressable printer, comprising: a. A buffer storage for storing a bitmap representation of information to be printed. B. A font storage for storing a bitmap representation of the character font in reduced form; c. A font statistics storage for storing Δx, Δy and character spacing statistics for the reduced form character font; d. A font parameter storage device for storing a character width, a height, and a font address parameter for a reduced format character font, wherein the font parameter storage device stores a width, a height, and a font address for a specified character in response to a specific character identifier. The generated font parameter storage, e. Font statistics storage and font parameter storage connected to And in response to a print command, checks the font statistic from a font statistical value memory x, y
A main processing unit capable of generating character positions and sending specific character identifiers to the font parameter storage unit; and f. Connecting to the main processing unit, buffer storage unit, font parameter storage unit, and font storage unit. And the bits retrieved from the font storage device in response to the x, y character position from the main processor, the width, height, and the font address from the font parameter storage device. A bitmap character generator capable of placing the map at x, y character locations in the buffer storage device, wherein the font parameter storage device is simultaneously addressable with a character identifier and stores width, height and font address information respectively. Three constant speed call storage units (RA
M) Bitmap generator. 2. The apparatus of claim 1, wherein the RAM is dual ported to allow the main processor to update its contents. 3. A font storage device containing a plurality of fonts and combining a character identifier code with the font identifier code to generate an identifier code used to address the font parameter storage device. The device of claim 1, wherein the device comprises a combination device. 4. The apparatus according to claim 3, further comprising a latch device for latching the identifier code. 5. The character identifier code may be a 7-bit or 8-bit code, the font identifier code may be a 5-bit or 6-bit code, respectively, and the combination device may include a 5-bit font identifier code. 4. The apparatus of claim 3 including a switching device for switching between a combined 8-bit character identifier code and a 7-bit character identifier code combined with a 6-bit font identifier code.