Patent Publication Number: US-4929933-A

Title: Digital color video monitor

Description:
BACKGROUND OF THE INVENTION AND PRIOR ART 
     This invention relates in general to color video monitors capable of accepting digital color input signals and particularly to a color video monitor that is capable of accepting signals formatted in different modes. 
     The rapid proliferation of color video monitors for use with computers having digital outputs has resulted in a number of different video color format schemes or modes, hereinafter referred to simply as formats or modes. For example, it is known to have a 16 color video format coupled with a horizontal scanning frequency of 15.75 KHz and a 64 color video format coupled with a 21.8 KHz scanning frequency. Other formats are also used and still others will certainly be provided in the future. It is also desirable to provide means for developing a monochromatic display, generally in either green or amber, in many applications to satisfy viewer&#39;s preferences. The IBM Corporation has also developed a distinctive video brown known as &#34;IBM brown&#34; for certain of its monitors and it is also desirable to be able to produce this video color on the CRT. 
     The commonly known 16 color format includes red (R), green (G) and blue (B) color signals and a common intensity (I) signal. The 64 color format has R, G and B color signals and red (r), green (g) and blue (b) individually intensity signals. The horizontal scanning frequency for the 16 color format is lower than that for the 64 color format and the polarity of the incomihg vertical synchronizing signal is used to identify the mode being used, i.e., 16 or 64 color. Additionally, it is desirable to provide the viewer with a control to adjust the overall brightness and contrast of the video display to his preference. 
     The monitor of the invention automatically adjusts for the color mode (in the preferred embodiment, either a 16 or 64 color format) and conditions the monitor operating circuits to function therewith. This is accomplished by means of a Programmable Read Only Memory (PROM) that has a plurality of video color inputs and functional inputs and a plurality of outputs with input addressable memory locations at which are stored binary words for supplying appropriate information to the outputs. 
     OBJECTS OF THE INVENTION 
     The principal object of the invention is to provide a novel color video monitor. 
     Another object of the invention is to provide a color video monitor that is automatically conditioned by incoming information for operation with different color video formats. 
     A further object of the invention is to provide a multi-mode color video monitor that is economical to manufacture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawing, the single FIGURE of which is a partial block, partial schematic representation of a color video monitor constructed in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawing, a color video monitor, generally designated 10, includes a plurality of color signal input terminals A0-A5 and function input terminals A6-A8 for receiving a corresponding plurality of digital video input signals and functional input signals, respectively. The signals may be from any suitable source, such as a computer 11. The video input terminals and functional input terminals correspond to address inputs of a PROM 14. PROM 14 includes a plurality of memory output terminals Q1-Q8 that supply digital logic level signals for controlling displayed video information on the cathode ray tube (CRT) 24 of the monitor. The digital video input signals supplied to PROM 14 are R, G and B and I/g, b, r (at terminals A0-A5), a mode select signal (at terminal A7) and a pair of signals for controlling blanking and the color mode of the CRT display (at terminals A6 and A8). This latter function is controlled by a 3-position switch 12 that is user actuatable among &#34;normal,&#34; &#34;amber&#34; and &#34;green&#34; positions. The RGB input signals relate to the primary colors R, G and B, whereas the r, g and b and I input signals relate to the brightness or intensity of the corresponding primary colors and overall display, respectively. When the display is supplied with input signals formatted in the 16 color mode, R, G, B and I are used, whereas when it is supplied with signals formatted in the 64 color mode, R, G, B, r, g and b are used. I and g share the A3 input terminal. The functional signal inputs will be discussed hereinafter. 
     The digital signals at the outputs of PROM 14 comprise R, G, B I, r, g, b and a Brown (for IBM brown) and a brightness compensation (BC) signal. The R and r signals are applied to R processing means 18, the B and b signals to B processing means 20 and the G and g signals to G processing means 22, shown in schematic form and enclosed by dashed lines. The outputs of the R, G and B processing means are applied to respective cathodes of CRT 24. The Brown signal is applied to G processing means 22 and the BC signal is applied to a user adjustment means 26 for enabling control of the CRT brightness and contrast. 
     The functional input terminals A6 and A8 of PROM 14 are supplied from the outputs of a pair of OR gates 15 and 16. The inputs to the ORs are supplied from switch 12 and a source of composite blanking signals (not shown). Movement of switch 12 among its positions, in conjunction with the blanking pulses, results in the A6 and A8 input terminals of PROM 14 being at the same low logic level (O) for a normal display and at opposite levels for a monochrome green or amber display, irrespecitve of the colors actually being received and at high levels during blanking. 
     As will be explained, brightness compensation is provided since it has been found that a monitor that is operated at 15.75 KHz tends to appear less bright (in the display area) than when it is opoerated at 21.8 KHz. The BC signal is used to change the brightness when operating in one color mode so that the brightness in both color modes is substantially the same. 
     Vertical sync input signals are applied to a vertical polarity detector circuit 30. The polarity of the incoming vertical sync is used to identify the color mode or format of the video signals. Polarity circuit 30 determines the polarity of the vertical sync signal and provides a high or low logic level signal to the A7 (mode select) input terminal of PROM 14 to select the 16 or 64 color mode. It also supplies a similar signal to a vertical deflection circuit (not shown) to assure that the vertical sync pulses developed for the monitor deflection circuits are of proper polarity irrespective of the polarity of the incoming vertical sync. The vertical polarity detector 30 may consist of a simple integrating network for accepting the vertical rate incoming sync signal and developing an output, the magnitude of which is determinative of whether the input sync signal is negative-going or positive-going. 
     PROM 14 includes a plurality of addressable memory locations, at each of which digital data, in the form of a binary word, is stored. The stored information develops appropriate logic level signals at corresponding output terminals of PROM 14 in accordance with the addressed input terminals. For example, the logic level signal applied to the 16/64 mode select input terminal A7 determines two groups of memory locations. The logic level signals applied to the A6 and A8 input terminals, in combination, define four subgroups of memory locations. The video logic level signals at the A0-A5 input terminals define unique memory locations within these groups and subgroups. The horizontal blanking function, which is applicable to both the 16 and 64 color modes, overrides all video information. The BC signal need only be present in either the 16 or 64 color mode to activate this function. It should be appreciated that the PROM is addressed, and memory information read out, at a pixel rate with the binary word stored at each memory address supplying all necessary output information. 
     As mentioned, an appropriate logic level mode select signal, i.e., a &#34;0&#34; or &#34;1&#34; is supplied by vertical polarity detector 30 and indicates whether the accompanying video information is in a 16 or a 64 color format. The mode select signal supplied to the A7 input terminal of PROM 14 selects the appropriate one of the two main memory locations in the PROM. 
     For descriptive purposes, only the G processing means 22 will be described in detail. It will be appreciated by those skilled in the art that the circuit arrangements (and descriptions) for R processing means 18 and B processing means 20 are substantially identical to those for G processing means 22. G processing means 22 includes an NPN transistor 36 having a load resistor 38 connected between its collector and a source of +88 V d.c. potential and an emitter that is connected in common with the collectors of a pair of NPN transistors 42 and 44. A source of +8 V d.c. bias voltage is connected to the base of transistor 36 and its collector is connected to the G cathode of CRT 24. The emitter of transistor 36 is connected to a bias arrangement, consisting of a potentiometer 32 an a resistor 34, for adjusting the d.c. bias level on the G cathode of CRT 24. The emitter of transistor 42 is connected by a resistor 46 to ground and its base is connected to a potentiometer 50 and to the G output (terminal Q2) of PROM 14. As illustrated by the transistor 51, the internal PROM arrangement provides an open collector connected source for the G output logic level signal. Th emitter of transistor 44 is similarly connected to ground by a resistor 48 and its base is connected to the g output (terminal Q5) of PROM 14. Here again, a symbolic showing of a transistor 53 within PROM 14 indicates that the g logic level signal is supplied from an open collector source. 
     User adjustment means 26 includes a PNP transistor 60 and NPN transistors 72 and 80. Transistors 72 and 80 have their collectors connected to +8 V d.c. whereas the collector of transistor 60 is connected to ground. The base of transistor 60 is connected through a resistor 62 to the BC output (terminal Q8) of PROM 14 and, through a resistor 64, to a contrast potentiometer 66, connected between +5 V d.c. and ground. The base of transistor 60 is also coupled to an automatic brightness limiter (ABL) circuit (not shown). The emitter of transistor 60 is connected through a diode 61 and a resistor 70 to +8 V d.c., with the junction of diode 61 and resistor 70 being connected to the base of transistor 72. The depiction of a transistor 55 internally connected to terminal Q8 of PROM 14 indicates an open collector connection. The base of transistor 72 is also connected to an intensity potentiometer 82 that is connected to the base of transistor 80. The emitters of transistors 72 and 80 are connected to ground through resistors 74 and 84, respectively. The emitter of transistor 72 is connected to a resistor 52 in G processor means 22. Resistor 52 is in a voltage divider including potentiometer 50 and a resistor 54. The junction of resistor 52 and potentiometer 50 is connected to the Brown output (terminal Q7 ) of PROM 14 and the depiction of transistor 57 indicates an open collector connection. Finally, the emitter of transistor 80 is connected through a resistor 56 to the base of transistor 44. 
     In operation, it will be noted that the r, g and b input signals are not present when the I signal is present and vice versa. The I signal is equal to r+b+g, and therefore, in the 16 color mode, the r, g and b output signals from PROM 14 are equal and are either logic level &#34;0&#34; or &#34;1&#34; depending upon the I signal. In the 64 color mode, the r, g and b output signals are determined by r, g and b input signals. The G and g output signals from terminals Q2 and Q5 of PROM 14 are applied to the bases of transistors 42 and 44, respectively. The parallel connected transistors 42 and 44 are in a cascode arrangement with transistor 36 for applying an appropriate signal to the G cathode of CRT 24. The mode select input signal to terminal A7 determines the 16 or 64 color mode. The BC signal is activated to change the bias on the base of transistor 60 and thereby affect the analog contrast potential supplied through transistor 72 to the base of transistor 42, which processes the G signal. The change in conduction of transistor 60 also changes the base potential of transistor 80, which supplies the base of transistor 44 to affect processing of the g signal. Thus the contrast and intensity are altered together to change the overall brightness and contrast of the display. (It should be borne in mind that similar changes simultaneously occur in the R and B processing means 18 and 20.) Potentiometers 66 and 82 provide the user with manual controls for adjusting the contrast and intensity of the display to suit different preferences or conditions. It will also be appreciated that the emitter resistors of transistors 42 and 44 are part of frequency sensitive circuits (not shown) for enabling changes in conduction of transistor 42 to primarily affect G signal contrast and changes in conduction of transistor 44 to affect intensity changes in the G signal. During operation where the BC signal is not desired, the open collector construction of PROM 14 presents a very high impedance at terminal Q8 which, therefore, has no effect on operation of transistor 60. The open collector construction enables the outputs of the PROM to be connected across the low level inputs of the transistors. 
     As mentioned previously, in response to an appropriate user input from switch 12, the CRT displays can be changed to monochromatic green or amber (IBM brown) by addressing different memory locations to provide the required signals from the PROM outputs. During horizontal blanking periods, still other memory locations are accessed, where binary data for disabling all video output signals from PROM 14 are stored. In the case of IBM brown being selected at switch 12, output terminal Q7 is activated to reduce the G signal level applied to transistor 42 and reduce the intensity of the G cathode signal to effect a shift in color temperature of the display to produce Brown. Under other conditions, the open collector arrangement of terminal Q7 effectively removes the PROM circuitry from the input circuit of transistor 42. 
     The actual programming of the PROM is straightforward and a complete listing thereof is included as an appendix. The use of open collector connected output sources in the PROM enables a significant reduction of parts in providing these functions to be user. 
     It is recognized that numerous modifications and changes in the described embodiment of the invention will be apparent to those skilled in the art without departing from its true spirit and scope. The invention is to be limited only as defined in the claims. 
     
                       APPENDIX                                                    
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HEX       HEX         HEX       HEX                                       
ADDRESS   OUTPUT      ADDRESS   OUTPUT                                    
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0000      40          0030      78                                        
0001      41          0031      79                                        
0002      42          0032      7A                                        
0003      03          0033      7B                                        
0004      44          0034      7C                                        
0005      45          0035      7D                                        
0006      46          0036      7E                                        
0007      47          0037      7F                                        
0008      40          0038      78                                        
0009      41          0039      79                                        
000A      42          003A      7A                                        
000B      43          003B      7B                                        
000C      44          003C      7C                                        
000D      45          003D      7D                                        
000E      46          003E      7E                                        
000F      47          003F      7F                                        
0010      78          0040      40                                        
0011      79          0041      42                                        
0012      7A          0042      42                                        
0013      7B          0043      42                                        
0014      7C          0044      42                                        
0015      7D          0045      42                                        
0016      7E          0046      42                                        
0017      7F          0047      42                                        
0018      78          0048      42                                        
0019      79          0049      42                                        
001A      7A          004A      42                                        
001B      7B          004B      42                                        
001C      7C          004C      42                                        
001D      7D          004D      42                                        
001E      7E          004E      42                                        
001F      7F          004F      42                                        
0020      40          0050      42                                        
0021      41          0051      42                                        
0022      42          0052      42                                        
0023      43          0053      42                                        
0024      44          0054      42                                        
0025      45          0055      42                                        
0026      46          0056      42                                        
0027      47          0057      42                                        
0028      40          0058      42                                        
0029      41          0059      42                                        
002A      42          005A      42                                        
002B      43          005B      42                                        
002C      44          005C      42                                        
002D      45          005D      42                                        
002E      46          005E      42                                        
002F      47          005F      42                                        
0060      42          008E      CE                                        
0061      42          008F      CF                                        
0062      42          0090      D0                                        
0063      42          0091      D1                                        
0064      42          0092      D2                                        
0065      42          0093      D3                                        
0066      42          0094      D4                                        
0067      42          0095      D5                                        
0068      42          0096      D6                                        
0069      42          0097      D7                                        
006A      42          0098      D8                                        
006B      42          0099      D9                                        
006C      42          009A      DA                                        
006D      42          009B      DB                                        
006E      42          009C      DC                                        
006F      42          009D      DD                                        
0070      42          009E      DE                                        
0071      42          009F      DF                                        
0072      42          00A0      E0                                        
0073      42          00A1      E1                                        
0074      42          00A2      E2                                        
0075      42          00A3      E3                                        
0076      42          00A4      E4                                        
0077      42          00A5      E5                                        
0078      42          00A6      E6                                        
0079      42          00A7      E7                                        
007A      42          00A8      E8                                        
007B      42          00A9      E9                                        
007C      42          00AA      EA                                        
007D      42          00AB      EB                                        
007E      42          00AC      EC                                        
007F      42          00AD      ED                                        
0080      C0          00AE      EE                                        
0081      C1          00AF      EF                                        
0082      C2          00B0      F0                                        
0083      C3          00B1      F1                                        
0084      C4          00B2      F2                                        
0085      C5          00B3      F3                                        
0086      C6          00B4      F4                                        
0087      C7          00B5      F5                                        
0088      C8          00B6      F6                                        
0089      C9          00B7      F7                                        
008A      CA          00B8      F8                                        
008B      CB          00B9      F9                                        
008C      CC          00BA      FA                                        
008D      DC          00BB      FB                                        
00BC      FC          00EC      C2                                        
00BD      FD          00ED      C2                                        
00BE      FE          00EE      C2                                        
00BF      FF          00EF      C2                                        
00C0      C0          00F0      C2                                        
00C1      C2          00F1      C2                                        
00C2      C2          00F2      C2                                        
00C3      C2          00F3      C2                                        
00C4      C2          00F4      C2                                        
00C5      C2          00F5      C2                                        
00C6      C2          00F6      C2                                        
00C7      C2          00F7      C2                                        
00C8      C2          00F8      C2                                        
00C9      C2          00F9      C2                                        
00CA      C2          00FA      C2                                        
00CB      C2          00FB      C2                                        
00CC      C2          00FC      C2                                        
00CD      C2          00FD      C2                                        
00CE      C2          00FE      C2                                        
00CF      C2          00FF      C2                                        
00D0      C2          0100      00                                        
00D1      C2          0101      03                                        
00D2      C2          0102      03                                        
00D3      C2          0103      03                                        
00D4      C2          0104      03                                        
00D5      C2          0105      03                                        
00D6      C2          0106      03                                        
00D7      C2          0107      03                                        
00D8      C2          0108      03                                        
00D9      C2          0109      03                                        
00DA      C2          010A      03                                        
00DB      C2          010B      03                                        
00DC      C2          010C      03                                        
00DD      C2          010D      03                                        
00DE      C2          010E      03                                        
00DF      C2          010F      03                                        
00E0      C2          0110      03                                        
00E1      C2          0111      03                                        
00E2      C2          0112      03                                        
00E3      C2          0113      03                                        
00E4      C2          0114      03                                        
00E5      C2          0115      03                                        
00E6      C2          0116      03                                        
00E7      C2          0117      03                                        
00E8      C2          0118      03                                        
00E9      C2          0119      03                                        
00EA      C2          011A      03                                        
00EB      C2          011B      03                                        
011C      03          014A      00                                        
011D      03          014B      00                                        
011E      03          014C      00                                        
011F      03          014D      00                                        
0120      03          014E      00                                        
0121      03          014F      00                                        
0122      03          0150      00                                        
0123      03          0151      00                                        
0124      03          0152      00                                        
0125      03          0153      00                                        
0126      03          0154      00                                        
0127      03          0155      00                                        
0128      03          0156      00                                        
0129      03          0157      00                                        
012A      03          0158      00                                        
012B      03          0159      00                                        
012C      03          015A      00                                        
012D      03          015B      00                                        
012E      03          015C      00                                        
012F      03          015D      00                                        
0130      03          015E      00                                        
0131      03          015F      00                                        
0132      03          0160      00                                        
0133      03          0161      00                                        
0134      03          0162      00                                        
0135      03          0163      00                                        
0136      03          0164      00                                        
0137      03          0165      00                                        
0138      03          0166      00                                        
0139      03          0167      00                                        
013A      03          0168      00                                        
013B      03          0169      00                                        
013C      03          016A      00                                        
013D      03          016B      00                                        
013E      03          016C      00                                        
013F      03          016D      00                                        
0140      00          016E      00                                        
0141      00          016F      00                                        
0142      00          0170      00                                        
0143      00          0171      00                                        
0144      00          0172      00                                        
0145      00          0173      00                                        
0146      00          0174      00                                        
0147      00          0175      00                                        
0148      00          0176      00                                        
0149      00          0177      00                                        
0178      00          01A7      83                                        
0179      00          01A8      83                                        
017A      00          01A9      83                                        
017B      00          01AA      83                                        
017C      00          01AB      83                                        
017D      00          01AC      83                                        
017E      00          01AD      83                                        
017F      00          01AE      83                                        
0180      80          01AF      83                                        
0181      83          01B0      83                                        
0182      83          01B1      83                                        
0183      83          01B2      83                                        
0184      83          01B3      83                                        
0185      83          01B4      83                                        
0186      83          01B5      83                                        
0187      83          01B6      83                                        
0188      83          01B7      83                                        
0189      83          01B8      83                                        
018A      83          01B9      83                                        
018B      83          01BA      83                                        
018C      83          01BB      83                                        
018D      83          01BC      83                                        
018E      83          01BD      83                                        
018F      83          01BE      83                                        
0190      83          01BF      83                                        
0191      83          01C0      00                                        
0192      83          01C1      00                                        
0193      83          01C2      00                                        
0194      83          01C3      00                                        
0195      83          01C4      00                                        
0196      83          01C5      00                                        
0197      83          01C6      00                                        
0198      83          01C7      00                                        
0199      83          01C8      00                                        
019A      83          01C9      00                                        
019B      83          01CA      00                                        
019C      83          01CB      00                                        
019D      83          01CC      00                                        
019E      83          01CD      00                                        
019F      83          01CE      00                                        
01A0      83          01CF      00                                        
01A1      83          01D0      00                                        
01A2      83          01D1      00                                        
01A3      83          01D2      00                                        
01A4      83          01D3      00                                        
01A5      83          01D4      00                                        
01A6      83          01D5      00                                        
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HEX           HEX                                                         
ADDRESS       OUTPUT                                                      
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01D6          00                                                          
01D7          00                                                          
01D8          00                                                          
01D9          00                                                          
01DA          00                                                          
01DB          00                                                          
01DC          00                                                          
01DD          00                                                          
01DE          00                                                          
01DF          00                                                          
01E0          00                                                          
01E1          00                                                          
01E2          00                                                          
01E3          00                                                          
01E4          00                                                          
01E5          00                                                          
01E6          00                                                          
01E7          00                                                          
01E8          00                                                          
01E9          00                                                          
01EA          00                                                          
01EB          00                                                          
01EC          00                                                          
01ED          00                                                          
01EE          00                                                          
01EF          00                                                          
01F0          00                                                          
01F1          00                                                          
01F2          00                                                          
01F3          00                                                          
01F4          00                                                          
01F5          00                                                          
01F6          00                                                          
01F7          00                                                          
01F8          00                                                          
01F9          00                                                          
01FA          00                                                          
01FB          00                                                          
01FC          00                                                          
01FD          00                                                          
01FE          00                                                          
01FF          00                                                          
1000          00                                                          
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