View source for VIDC1

{{Short description|Video display controller for Acorn computers}}
The '''VIDC1''' was a [[Video Display Controller]] chip created as an accompanying chip to the [[ARM architecture|ARM]] CPU used in [[Acorn Archimedes]] computer systems.<ref>{{Cite book |url=http://archive.computerhistory.org/resources/text/Acorn/Acorn_VIDCdatasheet.pdf |title=Acorn VIDC datasheet |publisher=Acorn Computers Limited |year=1986}}</ref><ref name=":0" /> Its successor, the [[VIDC20]], was later used in [[RiscPC]]s.<ref name=":0" />
==Video==
The VIDC1 offers [[Color depth|colour depths]] of 1, 2, 4 or eight bits per colour, allowing for 2, 4, 16 and 256 colour displays (the VIDC20 can offer up to approximately 16 million colours). A [[Palette (computing)|colour lookup table]] or palette register set of 16 [[12-bit computing|12-bit]] words was provided, offering a range of 4096 colours for each of the colours in those displays or modes employing up to 16 colours. The [[List of monochrome and RGB color formats#12-bit RGB|12 bits were split in three 4-bit RGB values]], with a 4-bit high speed [[Digital-to-analog converter|D/A converter]] for each of the three primary colours. However, in 256 colour modes, 4 bits of the colour data were hardware derived and could not be adjusted. The net result was 256 colours, covering a range of the 4096 available colours.<ref name=":0">{{Cite web|title=Riscos : Specifications of Legacy RISC OS machines|url=http://www.riscos.org/legacy/|access-date=2020-09-15|website=www.riscos.org}}</ref>
Since the device had no [[horizontal sync]] interrupt, it was difficult to display additional colours by changing the palette for each scan line, but not impossible, thanks to the 2&nbsp;MHz IOC timer 1.<ref>{{Cite web|url=https://groups.google.com/forum/#!topic/comp.sys.acorn.programmer/tf03F72mqNA|archive-url=https://archive.today/20120708165748/http://groups.google.com/group/comp.sys.acorn.programmer/browse_thread/thread/b5fd3717bda6a8d0/d4d3e151a783dffa?lnk=gst&q=ioc%23d4d3e151a783dffa#!topic/comp.sys.acorn.programmer/tf03F72mqNA|url-status=dead|title=Google Groups|website=groups.google.com|access-date=2020-12-21|archive-date=2012-07-08}}</ref> Many [[Demoscene|demos]] managed to display 4096 colours on screen, or in a sense more through [[Dither|dithering]].<ref>{{Cite web |date=2015-06-11 |title=Demos - Arcade BBS Filebase Listing |url=http://arcade.demon.co.uk/filepages/file32.htm |access-date=2022-12-22 |archive-url=https://web.archive.org/web/20150611100227/http://arcade.demon.co.uk/filepages/file32.htm |archive-date=2015-06-11 }}</ref>
The timing generator was fully programmable, and could be clocked with an 8 to 24&nbsp;MHz clock. Resolutions that could be supported were 1024x1024 in monochrome, 640x512 in 16 colors, or 640x256 in 256 colors.<ref name="pcw198708">{{ cite news | url=http://chrisacorns.computinghistory.org.uk/docs/Mags/PCW/PCW_Aug87_Archimedes.pdf | title=Acorn Archimedes | work=Personal Computer World | date=August 1987 | access-date=7 March 2021 | last1=Pountain | first1=Dick | pages=98–102,104 }}</ref>
It had also one hardware 32-pixel wide [[Sprite (computer graphics)|sprite]] with unlimited height (by default used for the mouse pointer), where each pixel is coded in two bits: value 0 is for transparency, and the three others are freely chosen from the 4096 colour palette.<ref>{{Cite web |date=April 10, 2009 |title=Acorn Archimedes A3000 |url=http://retro-treasures.blogspot.com/2009/04/acorn-archimedes-a3000.html |website=Retro Treasures}}</ref><ref>{{Cite web |url=http://www.drobe.co.uk/reference/early_datasheets/ |title=RISC OS News, Software and Information<!-- Bot generated title --> |access-date=2012-03-13 |archive-url=https://web.archive.org/web/20120713031919/http://www.drobe.co.uk/reference/early_datasheets/ |archive-date=2012-07-13 |url-status=dead }}</ref>
Acorn also used the VIDC chip in its laser printer interface podule, which featured in its [[RISC iX#A680 Technical Publishing System|Technical Publishing System]] solution. The VIDC was used to generate a high-resolution monochrome signal driven by "a gated form of the synchronised laser dot clock", assisted by a proprietary video laser interface chip, VLASER6. In the Technical Publishing System, the podule was "configured specifically to drive a {{nowrap|300 dpi}} Canon CX/SX print engine directly". Unlike conventional video, each raster line produced by the print engine effectively corresponded to a single video frame having only a single scanline, with vertical synchronisation occurring repeatedly over the course of generating a single page. An A4 page could have a resolution of 2432 dots horizontally, reproduced in 3440 lines vertically, requiring a total of over {{nowrap|8 million}} pixels.<ref name="acorn_tps_2">{{ cite book | url=http://chrisacorns.computinghistory.org.uk/docs/Acorn/Manuals/Acorn_TechnicalPublishingSystemTRMPt2.pdf | title=Acorn Technical Publishing System Technical Reference Manual | publisher=Acorn Computers Limited | date=July 1988 | access-date=27 May 2023 | issue=B | pages=137–138,150 }}</ref>
==Sound==
The VIDC also supported eight-channel stereo [[Logarithmic scale|logarithmic]] 8-bit [[Pulse-width modulation|PWM]] sound.
==References==
{{reflist}}
[[Category:Graphics chips]]
[[Category:Acorn Computers]]
[[Category:RISC OS]]