Multisync monitor: Difference between revisions

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A '''multiple-sync''' ('''multisync''') '''monitor''', also known as a '''multiscan''' or '''multimode''' monitor, is a [[Raster scan|raster-scan]] [[analog]] video [[Computer display|monitor]], generally used for computer displays, that can properly [[Synchronization|synchronise]] with multiple [[Horizontal scan rate|horizontal]] and [[Vertical synchronization|vertical]] [[scan 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|last=|first=|date=|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|url-status=live|archive-url=|archive-date=|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 set of scan rates. They are generally used for computer displays, but sometimes for television, and the terminology is mostly applied to [[Cathode-ray tube|CRT displays]] although the concept applies to other technologies.

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"MultiSync" flexibilityspecifically aswas computersa movedtrademark fromof earlierone standards such asof [[composite video]] and [[Color Graphics AdapterNEC|CGANEC's]], which utilized a single set refresh rate, to standards implementingfirst multiple-sync scanmonitors.<ref ratesname=":1" such as [[Enhanced Graphics Adapter|EGA]], [[VGA]] and [[SVGA]]./>

== Computers ==

The term "MultiSync" derives from an [[NEC]] trademark for one of the first multiple-sync monitors. Sond uses the terms "Multiscan" and "MultiFormat" instead, and Samsung uses the "SyncMaster" trademark.

=== History ===

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.

ComputersEarly thatdedicated did[[Computer notmonitor|computer use ordinary televisionsmonitors]] 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-rate IBMrates, identical to NTSC television. Early Macintosh monitors also used fixed scan rates.

Released inIn 1984, IBM's [[Enhanced Graphics Adapter|EGA]] requiredadded a second resolution which necessitated the use of a monitor whichsupporting supported thetwo scan raterates, ofthe original CGA rate as well as a second scan rate for EGA'sthe new video modes.<ref name=":0">{{Cite book|last=|first=|url=http://minuszerodegrees.net/oa/OA%20-%20IBM%20Enhanced%20Color%20Display%20(5154).pdf|title=IBM Enhanced Color Display Manual|publisher=|year=|isbn=|___location=|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>{{Cite book|last=Inc|first=InfoWorld Media Group|url=https://books.google.com/books?id=YToEAAAAMBAJ&lpg=PA39&dq=dual-sync%20EGA&pg=PA39#v=onepage&q&f=false|title=InfoWorld|date=1988-08-22|publisher=InfoWorld Media Group, Inc.|language=en}}</ref>

The firstNEC multisyncMultisync monitorwas -released in 1985 for use with the NECIBM MultisyncPC, -supporting wasa releasedwide inrange 1985of tosync providefrequencies supportincluding those for CGA, EGA, the various extended forms of those standards marketed by third party vendors, and standards yet to be released.<ref name=":1">{{Cite book|last=Inc|first=InfoWorld Media Group|url=https://books.google.com/books?id=mTwEAAAAMBAJ&lpg=PA61&dq=multisync&pg=PA61#v=onepage&q&f=false|title=InfoWorld|date=1986-10-27|publisher=InfoWorld Media Group, Inc.|language=en}}</ref>

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>{{Cite book|last=Inc|first=InfoWorld Media Group|url=https://books.google.com/books?id=YToEAAAAMBAJ&lpg=PA39&dq=dual-sync%20EGA&pg=PA39#v=onepage&q&f=false|title=InfoWorld|date=1988-08-22|publisher=InfoWorld Media Group, Inc.|language=en}}</ref> and by the late 80s all of the below computer video standards required monitors withwhich specificsupported frequencya small number of specific supportfrequencies:

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

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# [[VGA]]: 31.5&nbsp;kHz horizontal scan, 60 or 70&nbsp;Hz vertical scan (plus EGA/CGA modes)

# [[XGA]]: 35.5&nbsp;kHz horizontal scan, 87&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.

Soon after VGA's release, it began to be extended by third-party vendors and [[Video Electronics Standards Association|VESA]], developing into [[Super VGA]], which implemented both higher resolutions and different [[refresh rate]]s for a single given resolution.

By the late 1990s, monitorsgraphics 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|last=Inc|first=InfoWorld Media Group|url=https://books.google.com/books?id=DDwEAAAAMBAJ&lpg=PA14-IA1&dq=infoworld%2085hz&pg=PA14-IA1#v=onepage&q&f=false|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 the [[Power-on self-test|POST]]systems displaylike onthe theirIBM hostPC, systemsthe display would operate at the standard VGAlow moderesolution, such as the PC standard of 320x200 at 70&nbsp;Hz,. so aA monitor capable of thisdisplaying typeat both resolutions would need to be able to horizontally scan in a range from at least 31 to 68&nbsp;kHz.

In response, VESA established a standardized list of display resolutions, refresh rates, and accompanying timing for hardware manufacturers.<ref>{{Cite book|last=Inc|first=Ziff Davis|url=https://books.google.com/books?id=eX8w8B-OhIIC&lpg=PA151&dq=vesa%20display%20monitor%20timings&pg=PA177#v=onepage&q&f=false|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|last=|first=|date=|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|url-status=live|archive-url=|archive-date=|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 CGAsystems /having a small number of specific frequencies, like CGA, EGA /and VGA, standardsor built-in Macintosh graphics, supported limited fixed frequencies, e.g. 15.7&nbsp;kHzOn the IBM PC, 21.8&nbsp;kHzthese andwere 31.5&nbsp;kHzsignaled horizontalfrom rates,the graphics card to the detectedmonitor viathrough the polaritypolarities 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 original 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|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 upbetween tospecific aminimum specificand maximum horizontal and vertical raterates. 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|last=|first=|date=|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|url-status=live|archive-url=|archive-date=|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|last=|first=|date=|title=Standards FAQ|url=https://vesa.org/vesa-standards/standards-faq/|url-status=live|archive-url=|archive-date=|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.

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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 majority of LCDs accept only 60&nbsp;Hz to 75&nbsp;Hz vertical scan rates. In recent years, LCD monitors designed for gaming have appeared on the market offering vertical scan rates of 120&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 their specific max refresh rate.

== Television ==

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 ==