BACKGROUND
The use of computers in graphics design, computer-aided design (CAD) and other applications that required large, high-definition displays has spawned a parallel development of high-resolution monitors and other display devices. As computer- driven displays progressed, applications abounded in medical and scientific uses, air traffic control and many other fields. Early on the need to drive the display devices from test generators arose. The generators took the place of the drive computers and were designed to be universal. That is, imitate any of the computer-drivers in use and produce test signals and patterns based on the raster architecture that the computer used. The generators soon became a vital piece of test equipment in the design, manufacture, quality control and service of high resolution display units. A small number of manufacturers worked from the beginning to build generators to
meet the needs of the display builders. Leader is one of them. |
RGB ANALOG/DIGITAL
One area of commonality in the test generators is primary-color drive. That is, three separate drive signals for each of the Red, Green and Blue primary colors are provided. These signals are basically analog in nature although they may be at TTL or ECL voltage levels. The latter has lead to some confusion in referring to the RGB generators as digital. While it is true that the output signals for nearly all RGB generators are digitally-synthesized from a clock that operates at the period of the smallest pixel and output signals are at TTL, ECL and analog voltage levels, the output signals are essentially analog in nature. (A few early generators used analog techniques to produce the signals but these have disappeared from the scene.) LCD and flat screen displays may require a true digital drive, that is, 8 or 10-bit parallel feeds for each of the primaries. Leader Models LT 1615 and LT 1610A provide 8-bit parallel as well as analog and TTL level feeds. |
CONTROL
Control is applied to the selection of:
1.Program addresses,
2.On-off control of RGB,
3. Selection of sync in terms of composite or separate H and V, the addition of sync to a selected primary signal (sync-on-green being the most common),
4.Test pattern selection and
5.The design of test patterns as well as
6.Raster architecture. |
STAND-ALONE OPERATION
Of the foregoing list, all aspects of generator control are embodied in item 1, the selection of the program address. That is, the selection of the program address recalls from memory (ROM or RAM) all parameters in items 2-6. Hence, address selection sets up the generator to provide RGB signals with the proper RGB status, sync selection, test pattern selection and raster architecture (scan rates, pulse timing, etc.) for that particular program. All of the generators described in the following pages can operate as stand-alone units with the control of program selection only. This makes them ideal for assembly, QA and service applications where the operator is not required to alter signal parameters. Figure 1 shows Model LT 1610A. Its small footprint allows it to fit in any workplace and the single program keys select program numbers from up to 100 stored on a user-replaceable ROM. A readout of program number is provided. |
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Figure 1. Model LT 1610A
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REMOTE CONTROL
Figure 2 shows Model LT 1610-01, a remote control unit. It permits remote selection of program number, but also extends operator control to items 1 to 4. It allows the operator to select from a list of factory preset test patterns (to be used in place of the test pattern stored with the program number.) On-off and polarity inversion of RGB is provided and sync status and polarity may be set up. |
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Figure 2. Model LT 1610-01 Remote Control
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PROGRAMMABILITY AND PC CONTROL
Raster architecture, in terms of horizontal and vertical scan rates, sync timing and parameters, etc. varies with the application and continues to change rapidly as new display needs evolve. Thus a fundamental requirement of an RGB generator is that it can be programmed by the user to match present and future raster formats. This brings the aspect of user-friendliness to the fore and considerable progress has been made. Early generators required the user to be at home with computer design techniques and left monitor designers familiar with timing parameters in terms of microseconds and raster lines to struggle with conversions. The generators shown represent the latest in the evolution in RGB generator design in that a major part of the programming task is taken over by a PC operating in the familiar Windows* format. They make it easy for the user to set them to match any given raster architecture with a high degree of accuracy. The limit, in terms of the total number of pixels displayed, is determined by the highest dot-clock frequency of which the generator is capable. Raster formats are built in a natural sequence of entries and basic calculations such as the frequency of the dot clock are calculated automatically. The user may work in pixels, characters and lines or if it is more familiar, in timing parameters expressed in microseconds and milliseconds. The generator warns of entries that will not compute and switches to the entry most likely in error. Individual programs include pattern selection (in some cases custom user designed patterns) and the choice and polarity of sync pulses including pulses added to R, G or B feeds to form composite signals. |
MEMORY
In addition to programmability, the RGB generator must be capable of storing the programs that have been designed to meet the particular raster formats, sync requirements and pattern selection or designs. Each of Leader programmable generators operate with a random access memory (RAM) capable of storing 100 programs. The RAM is backed by an internal battery so that programs remain in memory for idle periods (no longer than a few months.) The RAM makes it possible to call up previously designed raster formats. It also allows temporary changes to be made. For example, blanking and sync timing can be made to trim the raster for particular purposes but the original design will remain in tact unless a purposeful effort is made to overwrite the original. Or the trimmed design can be filed separately by simply assigning a new program number. But there is a need to extend memory into more indestructible forms. For this reason, all Leader generators work from a pre-programmed read-only memory (ROM). These also store 100 programs. They are particularly useful for program archives and for use in assembly line work where local access to design changes is not desired. The ROM also provides a means of setting up a number of generators to the same parameters. Figure 3. PC display used to set up raster architecture when the LT 1610 is under PC control. |
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Figure 3. PC display used to set up raster architecture when the LT 1610 is under PC control
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The generators shown in the next few pages, Models LT 1610A, LT 1611,
LT 1612A, LT 1613, LT 1614 and LT 1615 are all capable of being fully programmed and controlled from your PC using a single cable RS232C link and software provided by Leader. This setup puts all design tools into the familiar Windows * format and provides complete, easy-to-follow steps to build the raster format, design custom test patterns and set up output signal conditions. Figure 3 shows the timing PC display, in this case set up to use dots (pixels) horizontally and lines vertically, but note that ms and ms are alternative options. |
ENCODERS
A natural follow-up to programmable RGB generators are encoders capable of accepting RGB inputs and producing fully encoded signals commonly used in broadcast systems such as NTSC and PAL. The Leaders new Model LT 1608 does just that and even extends operation into the analog form of the latest HDTV formats. It accepts analog GBR, composite sync and clock from the RGB generator and produces fully encoded NTSC or PAL, complete with subcarrier and burst, in composite and Y/C form. HDTV outputs are 3-wire components in YPbPr form complete with tri-level sync.
*Windows is a registered trademark of Microsoft Corporation in the United States and/or other countries.
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