US3729714A

US3729714A - Proportional space character display including uniform character expansion

Info

Publication number: US3729714A
Application number: US00155982A
Authority: US
Inventors: R Heard
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1971-06-23
Filing date: 1971-06-23
Publication date: 1973-04-24
Anticipated expiration: 1990-04-24
Also published as: FR2143010B1; DE2221705C3; DE2221705B2; DE2221705A1; GB1370065A; FR2143010A1

Abstract

A system for uniformally expanding a proportionally spaced character display in order to properly align the smallest characters of the character set without affecting the proportional relationship of the characters in the character set. An extra vertical scan line is added to the displayed characters at an escapement increment determined by the character of the character set requiring the greatest proportion of scan line expansion per character width in order to achieve proper character definition. Those characters requiring an additional unit of escapement to be properly defined utilize the added vertical scan lines and excess added vertical scan lines are distributed in the ''''white space'''' between characters. The added display columns have the same affect as increasing the number of scans per unit of character escapement.

Description

United States Patent 1 1 Heard [451 Apr. 24, 1973 PROPORTIONAL SPACE CHARACTER {75] Inventor: Roderick S. Heard, Lexington, Ky.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: June 23,19'

[21] Appl. No: 155,982

[52] US. Cl ..340/l72.5, 340/324 A [51} Int. Cl v.G06r 3/14 [58] Field of Search .340/1725, 324 A {56] References Cited UNITED STATES PATENTS 3,011,164 11/1961 Gerhardt ..340/324 A 3,281,822 10/1966 Evans ....340/324 A 3,423,749 1/1969 Newcumb. ....340/324 A 3,500,470 3/1970 Barker 340/324 A 3,509,817 5/1970 Sims 340/1725 X 3,546,681 12/1970 Korn.. ...,.340/172.5 3,588,872 6/1971 K0111 ..340/324 A .15 5 I ft) 1/ n" out; l 1 MM g t/menu r I 1. MMHMUR 7 RFGISlfR l 1 1 mm; lllCODi um! 5 i MODE '5 1 lonnrss INPUTS l ADDRESS 1 1 UECODE coumrn L r m mm count [1N1 SW11 HiSH 3,614,767 10/1971 Carrell ..340/324 A Primary Examiner-Paul .I. Henon Assistant ExaminerSydney R. Chirlin A!t0rney.l0hn W. Girvin. Jr. et a1.

(57] ABSTRACT A system for uniformally expanding a proportionally spaced character display in order to properly align the smallest characters of the character set without affecting the proportional relationship of the characters in the character set. An extra vertical scan line is added to the displayed characters at an escapement increment determined by the character of the character set requiring the greatest proportion of scan line expansion per character width in order to achieve proper character definition. Those characters requiring an additional unit of escapement to bev properly defined utilize the added vertical scan lines and excess added vertical scan lines are distributed in the white space" between characters. The added display columns have the same affect as increasing the number of scans per unit of character escapement.

4 Claims, 2 Drawing Figures 1 EXPANSION 1 mum 1 PROPORTIONAL SPACE CHARACTER DISPLAY INCLUDING UNIFORM CHARACTER EXPANSION CROSS REFERENCE TO RELATED APPLICATIONS The following applications are all assigned to the same assignee as the present application.

U.S. Pat. No. 3,654,609, filed Mar. 2, I970, entitled "Proportional Spacing Visual Editing System, Robert G. Bluethman, et al, inventors.

US. Pat. No. 3,648,271, filed Mar. 2, 1970, entitled "Visual Editing System Incorporating Selectable Letter Spacing Display and Associated Scale Display, Robert L. McConnell, et al, inventors.

BRIEF BACKGROUND OF INVENTION l. Field This invention relates to a proportionally spaced character display system and more particularly to means incorporated in such a system for properly aligning and representing displayed character symbols.

2. Description of the Prior Art Prior Art display editing systems such as those exemplified by US. Pat. No. 3,248,705 utilize standard spaced character display representations to indicate to the system operator how printed lines of standard spaced characters will appear on final printed output copy. The aforereferenced copending application to Robert G. Bluethman, et al, discloses a display editing system utilizing proportionally spaced character representations to indicate to the operator thereof how a final printed line of proportionally spaced characters will appear upon printing a final copy. The aforereferenced copending application to Robert L. McConnell, et al, describes a display editing system wherein both standard spaced character representations and proportionally spaced character representations can be alternatively selected. The proportionally spaced character display is utilized when the final output copy is to be printed on a printer incorporating proportionally spaced or weighted character sets. The standard display is selected when the output printer is a standard spacing printer. In either event, the display device is utilized to give the operator of the display system an indication as to how the final printed copy will appear. The operator may then actuate controls to change the appearance of the displayed copy and hence the final output copy to achieve a more desirable affect.

Various printing devices incorporating proportionally spaced character sets are available to be utilized to prepare the final output copy. The escapement increments utilized for the various printers differ from one another. That is, for example, the escapement of one printer system may be based on an escapement unit of one seventy-second inch while that of another printer may be based on an escapement unit of one-sixtieth inch. The relative escapement values for characters of a character set utilizing a one seventy-second inch escapement unit differ with respect to one another as compared to the relative escapement values of characters within a set designed for a printer using a one-sixtieth inch escapement unit. Additionally, various printers have a print condensation mode wherein a uniform value is subtracted from the number of escapement units which define various ones of the characters in order to compress the various lines of printing.

In order for the display editing system to be flexible so that it may be used in conjunction with the various output printers described above to provide display lines of proportionally spaced characters which yield an accurate representation of the appearance of a final printed line, it is necessary to display different proportionally weighted character sets in accordance with the type of output device to be selected. It is also desirous to utilize a minimum character generator to generate the various character sets in order to reduce the overall costs of the device.

Character generators of the prior art which could be utilized to generate a proportional character display are of two types. One prior art device is a monoscope which displays proportional characters. Various character sets could be selected for display by expanding the character font and selection device of prior art monoscopes. However, the costs of such a unit would be prohibitive for a multi-line multi-character font display. Another prior device is one which generates a dot matrix character pattern, a unique pattern being associated with each character of a character set. While such a device is less costly than a monoscope type of display, the increased number ofcharacters which must be defined in order to display a plurality of proportionally weighted character sets necessitates greater costs.

In order to reduce these costs, the same matrix character generator can be utilized to define the same character in each of the different character sets displayed. However, in utilizing such a scheme, some characters cannot be properly defined since the number of scan lines necessary to define the character exceeds the number of scan lines available when the number of scan lines is equal to the escapement value of the character. One solution to this problem would be to increase the number of total scan lines of the display by a factor of two. However, by doubling the density of the scan lines which define each character, the number of lines of display feasible with a given circuit speed are reduced. Another solution is to add a scan line column to each character. However, this destroys the positional relationship of text in successive lines since all characters are not the same width.

SUMMARY In order to overcome the aforenoted problems of the prior art and to provide an economical display system for displaying various proportionally weighted character sets in a manner that lines of displayed characters are representative of the appearance of final printed output copy, a character generator is provided which adds an additional vertical scan line within the line of displayed characters at a predetermined increment thereby increasing the number of scan lines available to define each character of a character set without destroying the positional relationship of characters displayed on adjacent lines. The escapement value of the character of the character set which requires the most additional scan lines per width value of the character for adequate character definition is utilized to define the predetermined increment thereby assuring that each character within the display lihe which requires an additional scan line has an additional scan line available for its use in order that the character may be properly defined. The added scan lines enable the same character generator to be utilized to define the characters of the various character sets.

The foregoing and other features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment as illustrated in the accompanying drawings.

In the Drawings:

FIG. 1 is a schematic block diagram of the propor tional space character display system including uniform character expansion.

FIG. 2 is a pictorial illustration of proportionally spaced characters which are displayed by the system of FIG. 1.

Referring now to FIG. I of the drawings, the propor tional spaced character display system including uniform character expansion is depicted. Characters to be displayed in lines of characters on the CRT display 11 are stored in memory I3. Each successive character of a line of characters to be displayed is gated from the memory 13 through the And gate 15 to the character register 17. The character in the character register provides an address input to the character generator decode unit 19 which in turn provides successive vertical scan line information which defines the character to be displayed to the scan data register 21. The scan line information stored in the scan data register 2] is serialized by the serializer 23, the output of which is applied to the video amplifier 25 which, in turn, provides a blank and unblank signal to the CRT display II.

The character located in the character register 17 is also provided as an address input to the escapement unit decode 31. This unit determines the number of escapement units associated with the character located in the character register in accordance with the character set selected. Assuming that the character in the character register 17 is defined by a number of vertical scan lines corresponding to the number of escapement units which define the character, the compare unit 33 will provide an output signal when the last vertical scan line of the character is complete. This output signal is utilized to gate the memory address counter 35 and the And gate 15 to cause the next successive character to be gated to the character register I7 from the memory 13.

Referring briefly to FIG. 2 of the drawings, a pictorial illustration of proportionally spaced characters displayed on the CRT display I] of FIG. I is shown. As can be seen, each character is made from elements ofa matrix which corresponds to a dot pattern generated on the CRT display. Assuming a vertical character sweep, the H character depicted would be serially generated on the screen of the CRT a vertical scan line at a time. That is, as the CRT beam sweeps downwardly over the leftmost portion of the character, the beam would be unblanked for 10 successive time intervals corresponding to the 10 vertically stacked elements of the first column of the character matrix. Thereafter, the beam would be returned to the uppermost position and caused to sweep through the elements of the second column where it would be unblanked only during its travel through the fifth vertical element. This process is repeated until the last scan line (always blank to assure adjacent character spacing) is complete, at which time the beam is advanced to form the next adjacent character, the character B.

Referring once again to FIG. 1 of the drawings, a dot clock 41 is gated by an oscillator and caused to periodically advance. Each dot clock time corresponds to a vertical display element so that the first ten dot clock times correspond to the ten vertical elements located within a single scan column of a character matrix. Additional dot clock times are necessary to cause return of the CRT beam back to the starting position of an adjacent vertical scan. When the dot clock 41 reaches a zero count, it indicates that the next successive vertical column of a character is ready to be displayed. The zero" output signal of the dot clock 41 advances the column clock 43 when the dot clock reaches its zero state. The column clock 43 is a binary counter providing an output indicative of the count stored therein. The output of the column clock 43 provides an address input to the character generator decode unit 19 thereby controlling the scan line of information which is gated to the scan data register 21. The foregoing description has related to the units which are employed to generate sequential vertical column scans to define successive characters. These units with the exception ofthe escapement unit decode 31 and compare unit 33 represent a conventional character generator, as would be utilized to generate standard spaced matrix characters and are described in the aforereferenced U.S. Pat. No. 3,648,271 and in U.S. Pat. No. 3,6l8,032. As mentioned above, the escapement unit decode 31 and the compare unit 33 operate to indicate the completion of a serial character display and hence initiate the display of the next character. These units are not necessary when displaying standard space display characters since each character has the same number of scan columns. However, since proportionally weighted characters are displayed, it is necessary to define the completion of each character displayed thereby necessitating the escapement unit decode 31 and the com pare unit 33. The operation of an escapement unit decode for displaying proportionally weighted characters is described in the afore referenced U.S. Pat. No. 3,648,271.

Assuming that the output printer has a one seventysecond inch escapement unit and that the character unit values of the character font vary from four units of escapement for the narrowest character to nine units of escapement for the largest character, the mode selection switch 51 would be placed in position A. Positioning the switch thusly effects successive display lines of characters which closely resemble the manner that the same lines of characters would appear on the one seventy-second inch output printer. That is, the relative widths of the displayed characters correspond to the relative widths of the printed characters and the display characters of successive lines align vertically in the same manner as those of corresponding printed lines. This positioning is achieved when the mode switch 51 is in position A by utilizing a character generator which causes a one-to-one relationship to exist between scan lines and escapement units of the characters displayed on the CRT display I I.

Since the smallest character of the one seventysecond inch system described above is four escapement units and, hence, four scan lines wide, it can be readily defined. Referring briefly again to FIG. 2 of the drawings, it can be seen that four scan lines are necessitated to display the letter I (including the blank scan line to the right of the character needed for intercharacter definition This character and others such as the letters L], j, and I require a minimum of four scan lines to be defined and cannot be adequately defined with three scan lines assuming one scan line is reserved for inter-character spacing. Hence, when an output printer is selected having relative escapement unit values of three escapement units to eight escapement units or one less than the escapement units of a one seventy-second inch printer (e.g. a one seventy-second inch printer with n] print condensation) some characters cannot be defined if the number of scan lines correspond to the number of escapement units which define the character. For example, a letter I would have a relative escapement value of four units on a one seventy-second inch printer and a value of three units on the same printer with n-l print condensation. it thus becomes apparent that the number of scan lines defining the character must be increased when it is desirous to display lines of characters as they would appear when printed on a one seventy-second inch printer operating in a print condensation mode.

Referring once again to FIG. I of the drawings, when the mode selector switch 51 is placed into position B thereby selecting a one seventy-second n-l character display, a signal is provided to the expansion clock 53 which is operative to cause additional scan lines to be distributed amongst the characters in a manner to be described. The expansion clock is a four stage binary ring counter, with selective switching to control the number of stages utilized. The secondary column clock 55 is responsive to the output signal of the And gate 57 which is, in turn, responsive to the output signal of the expansion clock 53. The And gate 57 is also responsive to the zero output signal of the dot clock 41 and provides a counting signal to the secondary column clock 55 whenever a signal is provided by the expansion clock 53. The secondary column clock 55 is a binary counter which provides an output signal indicative of the count stored therein. The expansion clock 53 provides an output signal so long as it is not advancing to its first count. Assuming the mode selector switch 51 to be on its 8 position, the expansion clock becomes a four-stage ring counter which is advanced with each zero output from the dot clock 41. When the counter is reset to its first count, no signal is provided to the And gate 57 and hence the secondary column clock 55 does not advance with the zero output of the dot clock.

It can be readily appreciated that the count in the secondary column clock 55 will be less than the actual number of scan lines which have been effected for a character as represented by the state of the column clock 43 since the secondary column clock 55 is inhibited from advancing whenever the expansion clock resets to its first count. Since the output signal from the secondary column clock 55 is compared by the compare unit 33 with the true escapement of the character in order to terminate a character display, extra scan columns are generated under the control ofthe column clock 43. That is, the number of vertical scan lines generated by the display device II for a character corresponds to the number registered by the column clock 43 which will exceed the number registered by the secondary column clock 55. Since the output signal of the secondary column clock is utilized to halt character generation when it corresponds to the value generated by the escapement unit decode 31, the number of extra scans per character corresponds to the difference between the value in the column clock 43 and the secondary column clock 55. The extra scans are utilized to further define the character. When the mode selector switch is placed in position 8, an extra scan column is added for every three columns required by each escapement value of the character.

Referring again to FIG. 2, it can be seen with respect to the lower case letter I which is defined as a three-unit character for a one seventy-second inch n-l display that a fourth scan will be added thereby insuring for the white space between the characters. Additionally, it can be appreciated that the same character generator decode unit 19 can be utilized to produce the letter I in both one seventy-second inch escapement display and in one seventy-second inch n-l escapement display. The following table represents the relationship of escapement units in one seventy-second inch 11-] to those in one seventy-second inch for a similar character and also specifies the guaranteed minimum number and the maximum number of columns which will be available for display ot'the character when utilizing the uniform expand feature of the present invention which adds an extra scan column for each three scan columns.

TABLE I Units in Equivalent Guaranteed Maximum Possible l/72" n-l Units in Minimum Number Number of Excess or l/" 1/72" ofColumns Columns Columns 3 4 4 4 O 4 S 5 6 l S 6 6 7 l 6 7 8 ll 1 7 8 9 IO 2 8 9 10 l l 2 It can be seen from the above table that the guaranteed minimum number of columns or scan lines available for displaying characters having a one seventysecond inch n-l escapement is equal to or exceeds the number of scan lines necessary to display a corresponding character having a one seventy-second inch escapement for which number of scan lines corresponds to the number of escapement units. Thus, the same character generator can be utilized for displaying characters in a one seventy-second inch representation or in a one seventy-second inch n-l representation. It can also be seen from the above table that the possible number of excess columns associated with each character having an escapement value of three in one seventy-second inch n-l is zero when the character generator utilizes the same character set as is utilized with a one seventysecond inch display. Where an eight unit one seventysecond inch n-l character is to be displayed, there are two possible excess columns. Additional white space may be added to the right-hand side of the character to thus utilize the two additional scan line columns. in the worst case, this could cause right edge character misalignment from line to line by only two scan lines and left edge misalignment by only one scan line.

Referring once again to FIGv 2 of the drawings, a line of five letter !'s are depicted. Assuming that a letter r is assigned an escapement value of three units for a one seventy-second inch n-l display, it will be appreciated that five of these characters displayed adjacently on a final printed page would utilize escapement units. Similarly, an eight unit letter H and a seven unit letter B printed adjacent to one another would also take up 15 escapement units. Assuming that the five letter (s are located on a first printed line and that the letters HB are located on the printed line immediately below and that the left edge of the first letter I aligns with the left edge of the letter H, the right hand edge of the last letter I would also align with the right hand edge of the letter B. As will be explained, this relationship is approximately maintained with a maximum error of one scan column at the left edge of characters and two scan columns at the right edge of characters by utilizing the display system ofthe present invention As noted above, an extra scan column is added for every three scan columns when utilizing the display system of the present invention with the mode selector switch 51 placed in position B. Thus scan columns are utilized to display the line ofletter l's. Additionally, if the H utilized the maximum number of columns noted in the aforegoing Table 1, it would require 11 scan columns to be displayed. In a similar manner, the letter B would require a total of 10 scan columns to be displayed. Thus, a total of 21 scan columns would be utilized to display the letters HB of the second line causing those characters to misalign by only one scan column from that which would be expected with the final printed output. As noted above, the maximum misalignment which can occur by utilizing the identical character generator utilized for a one seventy-second inch character display and adding the extra scan columns is one scan column at the left edge of a character. Since the extra scan columns are uniformly added throughout each display line, the misalignment errors are not cumulative and an approximate relation ship is obtained without necessitating a separate character generator for each type of escapement displayed.

Referring once again to P10. 1 of the drawings, it can be seen that when the mode selector switch 51 is placed in position A thereby selecting a one seventy-second inch escapement display, a signal is provided to the And gate 60 which inhibits the output signal of the dot clock 41 from advancing the expansion clock 53. A signal is also supplied to the escapement unit decode 31 which provides a character output decode ranging from four to nine escapement units. Since the expansion clock 53 is inhibited from advancing, it never moves to the first count; thus each output signal of the dot clock 41 is applied to the secondary column clock 55 as well as to the column clock 43. In this mode, there is a oneto-one relationship between scan lines and escapement units. Thus, when the number of columns which have been scanned as indicated by the secondary column clock 55 equals the escapement value as determined by the output signal from the escapement unit decode 31, the compare unit 33 provides a signal effecting the display ofthe next character.

When the mode selector switch S1 is placed in position B, the expansion clock 53 has a fours counter activated which advances with each output signal from the dot clock 41 indicating the completion of a scan line. When this counter resets to its first count, the gat ing signal applied to the And gate 57 is removed and the secondary column clock does not advance with the output of the dot clock. Thus, for every three scan lines completed, a fourth scan line is added. Since the column clock continues to advance, the character generator decode unit 19 is provided with a signal indicating that the next successive column is to be displayed. Assuming that a character having an escapement value of three (e.g. the letter 1) is to be displayed and that it is the first character of a line, the expansion clock 53 is set to a count of two with the line start reset signal. At the completion of the first vertical scan of the t, the dot clock 41 provides an output signal which causes the column clock 43 to advance thereby addressing the second column of the t in the character generator decode unit 19. The secondary column clock 55 also advances and the expansion clock 53 advances from a count of two to a count of three. The second column of the letter I is then displayed causing the column clock 43 to advance to address the third column of the character in the character generator decode unit 19. The secondary column clock also advances to indicate that two columns have been displayed while the expansion clock moves from a count of three to a count of four. After the third scan line is complete, the output of the dot clock 41 causes the column clock to advance to the fourth column and causes the expansion clock 53 to advance from a four state to a one state. When the expansion clock 53 moves to its first count, it provides a degating signal to the And gate 57 which prevents the secondary column clock 55 from advancing. Since the value of the secondary column clock 55 does not at this time equal the value established by the escapement unit decode 31, the column clock 43 causes an additional scan to be taken. It will be noted that the character generator is the same as that used for a one seventy-second inch escapement display and therefore has a fourth defined column (blank). Once this sweep is complete, the dot clock provides a further signal causing the expansion clock to advance to a two state and causing the secondary column clock and the column clock to both advance. At this point, the value stored in the secondary column clock is equal to that defined by the escape ment unit decode (three scans complete three escapement units) thereby causing the compare unit 33 to provide an output signal resetting the secondary column clock 55, the column clock 43, and providing a gating signal to the And gate 15 to cause the next data character to be displayed. When characters such as the letter B are displayed, it is possible to have two additional scans over that provided by the character generator when generating that character in a one seventy-second inch escapement display. The character generator decode unit 19 is responsive to such additional scans provided by the column clock to generate blank scans.

When the mode selector switch 5] is moved to position C, a threes counter is actuated in the expansion clock 53. That is, the expansion clock 53 counts to three before resetting to one and, in this manner, causes an additional scan line to be provided for each two scan lines of display. The following table is representative of escapement values of characters when utilized in a one seventy-second inch n--2 or in one-sixtieth inch n-l display and also represents the guaranteed minimum number of columns and maximum number of columns and possible excess columns.

'Necessitates removal of one scan line from character generator.

In a similar manner, when the mode selector switch is moved to position D, a twos counter is actuated which provides an additional scan line for each scan line of display and can be utilized when it is desired to display a representation of a one-sixtieth inch n-2 escapementsystem.

As is recognized by those skilled in the art, an optimum character set can be selected for display instead of utilizing the character set associated with a one seventy-second inch escapement display. For example, characters having relative values defined under the guaranteed minimum number of columns heading of Table I can be utilized as the character set defined by the character generator decode unit 19. If such a set were utilized, it would be necessary to provide an additional mode input signal to the character generator decode unit 19 to effect the reduction in scan lines of7, 8, and 9 unit escapement characters when operating in a one seventy-second inch escapement system. That is, for example, a 10 unit letter W as defined by the character generator decode unit 19 would be reduced to a 9 unit letter W when operating in a one seventysecond inch escapement display. This could be effected in designing the character such that one scan line could be removed without affecting its overall appearance.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the scope of the invention.

What is claimed is:

l. A proportionally spaced character display system comprising:

character set selection means for selecting one of a plurality of proportionally weighted character sets to be displayed;

storage means for storing successively addressable characters to be displayed;

escapement decode means responsive to the character set selection means and to the storage means for defining the relative width in scan lines of each addressed character in the storage means in accordance with the character set selected;

character generating means responsive to each addressed character in the storage means for generating successive fixed vertical scan line segments in accordance with the addressed character, the number of vertical scan line segments generated depending upon the addressed characterscan lme adding means responswe to the character set selection means and to the character generating means for providing a scan line add signal for every predetermined number of scan lines generated when a first character set is selected and for providing no scan line add signal when a second character set is selected;

said character generating means being further responsive to said scan line add signal for generating an additional vertical scan line segment; character termination means responsive to the escapement decode means and the character generating means for addressing the next successively addressable character in said storage means when the number of vertical scan line segments generated by the character generator means equals the defined relative width in scan lines.

2. The proportionally spaced character display system set forth in claim 1 wherein said character generating means distributes said additional vertical scan line segments at the end of a generated character.

3. The proportionally spaced character display system set forth in claim 1 wherein said scan line adding means being further responsive to said character set selection means for providing a scan line add signal for a second predetermined number of scan lines when a third character set is selected.

4. The proportionally spaced character display system set forth in claim 1 wherein said predetermined number of scan lines corresponds to the width in scan lines of the smallest character in the first character set which character cannot be adequately defined by a corresponding number of vertical scan line segments.

a s a s e

Claims

1. A proportionally spaced character display system comprising: character set selection means for selecting one of a plurality of proportionally weighted character sets to be displayed; storage means for storing successively addressable characters to be displayed; escapement decode means responsive to the character set selection means and to the storage means for defining the relative width in scan lines of each addressed character in the storage means in accordance witH the character set selected; character generating means responsive to each addressed character in the storage means for generating successive fixed vertical scan line segments in accordance with the addressed character, the number of vertical scan line segments generated depending upon the addressed character; scan line adding means responsive to the character set selection means and to the character generating means for providing a scan line add signal for every predetermined number of scan lines generated when a first character set is selected and for providing no scan line add signal when a second character set is selected; said character generating means being further responsive to said scan line add signal for generating an additional vertical scan line segment; character termination means responsive to the escapement decode means and the character generating means for addressing the next successively addressable character in said storage means when the number of vertical scan line segments generated by the character generator means equals the defined relative width in scan lines.