Multisync monitor: Difference between revisions

Revision as of 02:44, 13 December 2014

Latest revision as of 04:45, 12 January 2025

(33 intermediate revisions by 20 users not shown)

Line 1:

{{Short description|Analog video monitor}}

A '''multisync monitor''' or '''multiscan monitor''' is a [[Computer display|monitor]] that can properly [[Synchronization|synchronise]] with various [[Horizontal scan rate|horizontal]] and [[Vertical synchronization|vertical]] scan [[Frequency|frequencies]].<ref>{{cite web|title=13 What's the difference between fixed frequency and multisynchronous monitors?|url=http://stason.org/TULARC/pc/video-faq/13-What-s-the-difference-between-fixed-frequency-andmultisynchronous-monitors.html}} 070808 stason.org</ref> In contrast, fixed frequency monitors can only synchronise with a specific horizontal and vertical frequency, limiting their flexibility.

{{More citations needed|date=May 2023}}

A '''multiple-sync''' ('''multisync''') '''monitor''', oralso known as a '''multiscan''' or monitor'''multimode''' monitor, is a [[Raster scan|raster-scan]] [[analog device|analog]] video [[Computer display|monitor]] that can properly [[Synchronization|synchronise]] with variousmultiple [[Horizontal scan rate|horizontal]] and [[Analog television#Vertical synchronization|vertical]] scan [[FrequencyVertical scan rate|frequenciesscan rate]]s.<ref>{{cite web|title=13 What's the difference between fixed frequency and multisynchronous monitors?|url=http://stason.org/TULARC/pc/video-faq/13-What-s-the-difference-between-fixed-frequency-andmultisynchronous-monitors.html}} 070808 stason.org</ref><ref>{{Cite web|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|access-date=2020-08-16|website=VESA - Interface Standards for The Display Industry|language=en-US|quote=Multimode monitors can measure the incoming sync signal frequencies and thus sync to any frequency within their range of operation.}}</ref> In contrast, fixed frequency monitors can only synchronise with a specific horizontalset andof verticalscan frequencyrates. They are generally used for computer displays, limitingbut theirsometimes for television, and the terminology is mostly applied to [[Cathode-ray tube|CRT displays]] although the concept applies to other flexibilitytechnologies.

Multiscan computer monitors appeared during the latemid 1980s, offering flexibility as computer video hardware shifted from producing a single fixed scan rate to multiple possible scan rates.<ref>{{cite web |title=MultiSync 25th Anniversary -{{Snd}} The Evolution of the MultiSync |url=http://www.nec-display.com/ap/en_display/25th/}}</ref>, offering|url-status=dead flexibility|archive-url=https://web.archive.org/web/20211101010646/https://www.nec-display.com/ap/en_display/25th/ as|archive-date=1 computersNovember moved2021 from earlier|website=NEC standardsDisplay such as [[PAL]]Solutions, [[NTSC]]Ltd.}}</ref> and"MultiSync" [[Colorspecifically Graphicswas Adapter|CGA]]a totrademark higherof scan-rateone standards such asof [[Enhanced Graphics AdapterNEC|EGANEC's]], [[VGA]]first and [[SVGA]]. Normally, a different fixedmultiple-frequencysync monitor was required for each of these standardsmonitors. <!--ref thename=":1" wiki articles on VGA etc. should already cite all needed information --/>

== Computers ==

# [[PAL], [[NTSC], [[Color Graphics Adapter|CGA]]: ~15&nbsp;kHz horizontal scan, 50-60&nbsp;Hz vertical scan

# [[Enhanced Graphics Adapter|EGA]]: ~23&nbsp;kHz horizontal scan

# [[VGA]]: ~31&nbsp;kHz horizontal scan, 60-70&nbsp;Hz vertical scan

# [[SVGA]]: 31&nbsp;kHz - 100&nbsp;kHz+ horizontal scan, 50&nbsp;Hz - 120&nbsp;Hz+ vertical scan

=== History ===

By the late 90s, multiscan monitors had become standard for personal computers, supporting a range of resolutions and refresh rates. A typical screen resolution of the time was 1024x768 at 85Hz <!-- need to find archived personal computer manufacturer product listings and web browser statistics for citation -->, requiring a horizontal scan rate over 85kHz,<ref>{{cite web|title=Modeline Calculator|url=http://www.arachnoid.com/modelines/}}</ref> yet during system boot the [[Power-on self-test|POST]] display and [[operating system]] splash screen would be displayed at the standard VGA 31kHz. Many [[MS-DOS]] and [[Windows]] computer games of the time would also switch to a lower resolution for greater compatibility, more colours, improved performance or to reduce the [[video memory]] required by the [[frame buffer]].

Early [[home computer]]s output video to ordinary televisions or [[composite monitor]]s, utilizing television display standards such as [[NTSC]], [[PAL]] or [[SECAM]]. These display standards had fixed scan rates, and only used the vertical and horizontal sync pulses embedded in the video signals to ensure synchronization, not to set the actual scan rates.

Early dedicated [[computer monitor]]s still often relied on fixed scan rates. IBM's original 1981 [[IBM Personal Computer|PC]], for instance, was sold with a choice of two video cards ([[IBM Monochrome Display Adapter|MDA]] and [[Color Graphics Adapter|CGA]]) which were intended for use with custom IBM monitors which still used fixed scan rates. The CGA timings were identical to NTSC television, whereas the MDA card used a custom timing for higher resolution to provide better text quality. Early Macintosh monitors also used fixed scan rates.

Depending on the design of the monitor, there may be several discrete frequencies supported. For example, a monitor designed for use with CGA, EGA and VGA standards could elect to support 15kHz, 23kHz and 31kHz horizontal scan rates. Alternatively, the monitor may be designed to support a continuous range from 15kHz to 31kHz. <!-- links to product manuals for old multisyncs would be useful here, or usenet -->

In 1984, IBM's [[Enhanced Graphics Adapter|EGA]] added a second resolution which necessitated the use of a monitor supporting two scan rates, the original CGA rate as well as a second scan rate for the new video modes.<ref name=":0">{{Cite book|url=http://minuszerodegrees.net/oa/OA%20-%20IBM%20Enhanced%20Color%20Display%20(5154).pdf|title=IBM Enhanced Color Display Manual|pages=1}}</ref> This monitor as well as others that could be manually switched between these two sync rates were known as dual-scan displays.<ref name="InfoWorld">{{Cite book|url=https://books.google.com/books?id=YToEAAAAMBAJ&dq=dual-sync%20EGA&pg=PA39|title=InfoWorld|date=1988-08-22|publisher=InfoWorld Media Group, Inc.|language=en}}</ref>

A multiscan monitor does not need to support all possible video formats. Most modern multiscan computer monitors support a nearly-continuous range of horizontal scan frequencies from 31kHz up to 100kHz+, omitting support for the older 15kHz - 23kHz standards. <ref>{{cite web|title=comp.sys.amiga.misc usenet post circa 1992|url=https://groups.google.com/forum/#!search/Multisync/comp.sys.amiga.misc/ktCKO1yqiaY/WB2ky14SDEYJ}}</ref> <ref>{{cite web|title=comp.sys.acorn.hardware usenet post circa 2010|url=https://groups.google.com/forum/#!search/Multisync/comp.sys.acorn.hardware/ZFi8regDZeo/gEGWCHGWLm8J}}</ref>

The NEC Multisync was released in 1985 for use with the IBM PC, supporting a wide range of sync frequencies including those for CGA, EGA, various extended forms of those standards marketed by third party vendors, and standards yet to be released.<ref name=":1">{{Cite book|url=https://books.google.com/books?id=mTwEAAAAMBAJ&dq=multisync&pg=PA61|title=InfoWorld|date=1986-10-27|publisher=InfoWorld Media Group, Inc.|language=en}}</ref>

Fixed-frequency [[Cathode ray tube|CRT]] monitors, and multiscan CRT monitors that only support a set of frequencies, may upon receiving scan frequencies outside design limits cause damage to the monitor. This is especially true for horizontal scanrate, which in CRT monitors is associated with higher voltages and power levels. A resonant circuit is commonly employed, restricting the allowable horizontal scan rates to one or more very narrow ranges. Not all fixed-frequency monitors are vulnerable to damage, but it is never safe to assume this. Most modern multiscan monitors are [[microprocessor]] controlled and will refuse to attempt to synchronise to an unsupported scan rate, which usually protects them from damage.

IBM's 1987 [[Video Graphics Array|VGA]] standard, in turn, expanded to three fixed scan rates. At this point, PC and Mac owners with multiple graphics cards required unique monitors for each of them,<ref name="InfoWorld"/> and by the late 80s all of the below computer video standards required monitors which supported a small number of specific frequencies:

It is important to remember that when the "refresh rate" setting in a computer operating system is increased, both the horizontal and vertical scan rates increase together. Even although monitors are relatively tolerant of a range of vertical refresh rates, it may take the horizontal scan rate out of range and potentially cause damage.

<!-- In a fixed frequency monitor, even a little bit off horizontal frequency can cause a significant current increase, particularly if the frequency is too low. The range of faults are far wider than burned out transformers as the previous version of this article suggested. The flyback, yoke or power transformer could burn out, but other faults can occur instead or in addition to transformer faults, for example a blown HOT, damaged caused by out-of-range power supply voltages, and arcing damage to the tube or flyback assembly from too high EHT or focus voltages. -->

# [[PAL]], [[NTSC]], [[Color Graphics Adapter|CGA]]: ~15.7&nbsp;kHz horizontal scan, 50- or 60&nbsp;Hz vertical scan

The terms "multisync" or "multiscan" do not apply to [[LCD]] monitors in the same way they do to [[Cathode ray tube|CRT]] monitors. LCD monitors are [[fixed-pixel monitors]]. For compatibility with boot screens and legacy software, stand-alone LCD monitors are usually required to support VGA scan rates in addition to their native resolution. In order to support the lower resolutions, a circuit is used to convert the incoming signal to the monitor's native resolution. The resulting image either appears in a small 1:1 pixel mapped window, or more commonly is stretched to fill the screen. In the latter case, the circuitry is referred to as a [[Video scaler|scaler]]. <!-- scaler article has all the citations -->

# [[Enhanced Graphics Adapter|EGA]]: ~2315.7&nbsp;kHz (CGA compatible mode) or 21.8&nbsp;kHz horizontal scan, 60&nbsp;Hz vertical scan

# [[VGA]]: 31.5&nbsp;kHz horizontal scan, 60 or 70&nbsp;Hz vertical scan. No support for CGA/EGA timings. CGA/EGA resolutions are transmitted to the monitor at VGA compatible timings.

# [[VGAXGA]]: ~3135.5&nbsp;kHz horizontal scan, 60-7087&nbsp;Hz (43.5&nbsp;Hz interlaced) vertical scan (plus VGA modes)

# Many different display formats for Macintosh, Sun, NeXT, and other microcomputers

After 1987's [[Video Graphics Array|VGA]]. the IBM market began to develop [[Super VGA]] cards which used many different scan rates, culminating in the [[VESA BIOS Extensions|VBE]] which established standardized methods for outputting many different resolutions from one card, eventually becoming the [[Generalized Timing Formula]] which permitted graphics cards to output arbitrary resolutions.

While stand-alone LCD monitors generally accept a wide range of horizontal scan rates, the same is not true of the vertical scan rate. The vast majority of LCDs accept only 60Hz to 70Hz vertical scan rates. In recent years, LCD monitors designed for gaming have appeared on the market offering vertical scan rates of 120Hz and up. <ref>{{cite web|title=List of 120Hz monitors - Includes 144Hz, 240Hz Blur Busters|url=http://www.blurbusters.com/faq/120hz-monitors/}}</ref> These monitors are referred to by the term "120Hz" (or the applicable refresh rate) rather than "multiscan."

By the late 1990s, graphics cards for microcomputers were available with specs ranging from 1024x768 at 60&nbsp;Hz, to at least 1600x1200 at 85&nbsp;Hz.<ref>{{Cite book|url=https://books.google.com/books?id=DDwEAAAAMBAJ&dq=infoworld%2085hz&pg=PA14-IA1|title=InfoWorld|date=1997-12-15|publisher=InfoWorld Media Group, Inc.|language=en}}</ref> In addition to these higher resolutions and frequencies, during system boot on systems like the IBM PC, the display would operate at standard low resolution, such as the PC standard of 720x400 at 70&nbsp;Hz. A monitor capable of displaying at both resolutions would need to be able to horizontally scan in a range from at least 31 to 68&nbsp;kHz.

MultiSync is a trademark of [[NEC]].

In response, VESA established a standardized list of display resolutions, refresh rates, and accompanying timing for hardware manufacturers.<ref>{{Cite book|url=https://books.google.com/books?id=eX8w8B-OhIIC&dq=vesa%20display%20monitor%20timings&pg=PA177|title=PC Mag|date=July 1993|publisher=Ziff Davis, Inc.|language=en}}</ref> This was superseded by VESA's [[Generalized Timing Formula]], which provided a standard method to derive the timing of an arbitrary display mode from its sync pulses,<ref>{{Cite web|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|access-date=2020-08-16|website=VESA - Interface Standards for The Display Industry|language=en-US|quote=Q: How will GTF help the monitor automatically set itself to any timing format? / A: GTF defines the relationship between syncs and video signals at any frequency of operation. The display can measure the incoming sync frequency, and thus can predict where the image will start and finish, even though it may not have been preset at that operating point.}}</ref> and this in turn was superseded by VESA's [[Coordinated Video Timings]] standard.

=== Implementation ===

Early multisync monitors designed for use with systems having a small number of specific frequencies, like CGA, EGA and VGA, or built-in Macintosh graphics, supported limited fixed frequencies. On the IBM PC, these were signaled from the graphics card to the monitor through the polarities of one or both H- and V-sync signals sent by the video adapter.<ref name=":0" />

Later designs supported a continuous range of scan frequencies, such as the NEC Multisync which supported horizontal scan rates from 15&nbsp;to 31&nbsp;kHz<ref name=":1" /> derived from the sync signal timing rather than the polarity of the sync signals.<ref>{{Cite web|title=PC Mag 1987-03-31 : Free Download, Borrow, and Streaming|url=https://archive.org/details/PC-Mag-1987-03-31|access-date=2020-08-16|website=Internet Archive|date=31 March 1987 |language=en}}</ref> Displays like these could be used on multiple platforms and video cards as long as the frequencies were within range.

Modern monitors produced using the VESA frequency standards generally support arbitrary scan rates between specific minimum and maximum horizontal and vertical rates. Most modern multiscan computer monitors have a minimum horizontal scan frequency of 31&nbsp;kHz.<ref>{{Cite web|title=Converters {{!}} RetroRGB|url=https://www.retrorgb.com/converters.html|access-date=2020-08-16|language=en-US}}</ref>

In both multisync and fixed-sync monitors, timing is important to prevent image distortion and even damage to components.<ref>{{Cite web|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|access-date=2020-08-16|website=VESA - Interface Standards for The Display Industry|language=en-US|quote=Sync signals for displays drastically affect the quality, performance and even reliability of CRT displays. Even small differences in timing parameters can significantly affect image position and size, causing problems for the user. Difference in blanking times can lead to excessive power dissipation and electrical stress in the scanning circuits, or at the other extreme, incomplete or distorted images being displayed.}}</ref> Most modern multiscan monitors are [[microprocessor]] controlled<ref>{{Cite web|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|access-date=2020-08-16|website=VESA - Interface Standards for The Display Industry|language=en-US|quote=In order to identify the mode, most present day multiple frequency monitors use a simple microcontroller to measure syncs.}}</ref> and will refuse to attempt to synchronise to an unsupported scan rate, which usually protects them from damage.

=== Non-CRT monitors ===

The multisync concept applies to non-CRT monitors, such as [[LCD]]s, but is implemented differently.

LCD monitors are [[Fixed pixel display|fixed-pixel displays]], where the number of rows and columns displayed on the screen are constant, set by the construction of the panel. When the input signal has a resolution that does not match the number of pixels in the display, the LCD controller must still populate the same number of image elements.

This is accomplished either by [[Video scaler|scaling]] the image up or down as needed, creating a picture that does not have a 1:1 relationship between LCD image elements and pixels in the original image, or by displaying the image unscaled in the center of the monitor, filling the spaces on all sides with black pixels.

While stand-alone LCD monitors generally accept a wide range of horizontal scan rates, the same is not true of the vertical scan rate. The vast majority of LCDs accept only 60Hz60&nbsp;Hz to 70Hz75&nbsp;Hz vertical scan rates. In recent years, LCD monitors designed for gaming have appeared on the market offering vertical scan rates of 120Hz120&nbsp;Hz and up. <ref>{{cite web|title=List of 120Hz monitors -{{Snd}} Includes 144Hz, 240Hz Blur Busters|url=http://www.blurbusters.com/faq/120hz-monitors/}}</ref> These monitors are usually referred to by thetheir termspecific "120Hz" (or the applicablemax refresh rate) rather than "multiscan."

== Television ==

{{Unreferenced section|date=May 2023}}

CRT televisions are typically designed to operate only with the video standard of the country they are sold in ([[PAL]], [[NTSC]], [[SECAM]]), but some sets, particularly broadcast monitors, can operate on multiple standards.

== References ==

Line 31 ⟶ 57:

* [http://www.webopedia.com/TERM/M/multiscanning_monitor.html Multiscanning monitor] webopedia.

[[Category:DisplayElectronic display devices]]

[[Category:Graphics hardware]]

{{Compu-graphics-stub}}