Multisync monitor: Difference between revisions

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{{Short description|Analog video monitor}}

A '''multiple-sync''' ('''multisync''') '''monitor''', also known as a '''multiscan''' or '''multimode''' monitor, is a [[Raster scan|raster-scan]] [[analog device|analog]] video [[Computer display|monitor]] that can properly [[Synchronization|synchronise]] with multiple [[Horizontal scan rate|horizontal]] and [[Vertical synchronization|vertical]] [[Vertical scan rate|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.

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

A '''multiple-sync''' ('''multisync''') '''monitor''', also known as a '''multiscan''' or '''multimode''' monitor, is a [[Raster scan|raster-scan]] [[analog device|analog]] video [[Computer display|monitor]] that can properly [[Synchronization|synchronise]] with multiple [[Horizontal scan rate|horizontal]] and [[Analog television#Vertical synchronization|vertical]] [[Vertical scan rate|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 mid 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/ |url-status=dead |archive-url=https://web.archive.org/web/20211101010646/https://www.nec-display.com/ap/en_display/25th/ |archive-date=1 November 2021 |website=NEC Display Solutions, Ltd.}}</ref> "MultiSync" specifically was a trademark of one of [[NEC|NEC's]] first multiple-sync monitors.<ref name=":1" />

== Computers ==

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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 [[Computercomputer monitor|computer monitors]]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.

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|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 name="InfoWorld">{{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 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|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|firstname="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 which supported a small number of specific frequencies:

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

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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.

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|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 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.

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 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|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 ===

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== 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.

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

[[Category:DisplayElectronic display devices]]

[[Category:Graphics hardware]]