Engineering:VIDC1
The VIDC1 was a Video Display Controller chip created as an accompanying chip to the ARM CPU used in Acorn Archimedes computer systems.[1][2] Its successor, the VIDC20, was later used in RiscPCs.[2]
Video
The VIDC1 offers 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 colour lookup table or palette register set of 16 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 12 bits were split in three 4-bit RGB values, with a 4-bit high speed 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.[2]
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 MHz IOC timer 1.[3] Many demos managed to display 4096 colours on screen, or in a sense more through dithering.[4]
The timing generator was fully programmable, and could be clocked with an 8 to 24 MHz clock. Resolutions that could be supported were 1024x1024 in monochrome, 640x512 in 16 colors, or 640x256 in 256 colors.[5]
It had also one hardware 32-pixel wide 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.[6][7]
Acorn also used the VIDC chip in its laser printer interface podule, which featured in its 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 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 8 million pixels.[8]
Sound
The VIDC also supported eight-channel stereo logarithmic 8-bit PWM sound.
References
- ↑ Acorn VIDC datasheet. Acorn Computers Limited. 1986. http://archive.computerhistory.org/resources/text/Acorn/Acorn_VIDCdatasheet.pdf.
- ↑ 2.0 2.1 2.2 "Riscos : Specifications of Legacy RISC OS machines". http://www.riscos.org/legacy/.
- ↑ "Google Groups". https://groups.google.com/forum/#!topic/comp.sys.acorn.programmer/tf03F72mqNA.
- ↑ "Demos - Arcade BBS Filebase Listing". 2015-06-11. http://arcade.demon.co.uk/filepages/file32.htm.
- ↑ Pountain, Dick (August 1987). "Acorn Archimedes". Personal Computer World: pp. 98–102,104. http://chrisacorns.computinghistory.org.uk/docs/Mags/PCW/PCW_Aug87_Archimedes.pdf.
- ↑ "Acorn Archimedes A3000". April 10, 2009. http://retro-treasures.blogspot.com/2009/04/acorn-archimedes-a3000.html.
- ↑ "RISC OS News, Software and Information". http://www.drobe.co.uk/reference/early_datasheets/.
- ↑ Acorn Technical Publishing System Technical Reference Manual. Acorn Computers Limited. July 1988. pp. 137–138,150. http://chrisacorns.computinghistory.org.uk/docs/Acorn/Manuals/Acorn_TechnicalPublishingSystemTRMPt2.pdf. Retrieved 27 May 2023.
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