VIDC1

The VIDC1 offers colour depths of 1, 2, 4 or 8 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 1024×1024 in monochrome, 640×512 in 16 colours, or 640×256 in 256 colours.^[5] The high-resolution monochrome output was achieved by exposing pixel data in parallel via the four red channel output signals. Each group of four pixels would be presented at a rate of 24 MHz, and this data would then be serialised at a rate of 96 MHz, taking each pixel in turn from the exposed pixel values to generate the output signal.^{[1]: 29–30}

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 module, 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 module 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]

The VIDC also supported eight-channel stereo logarithmic 8-bit PWM sound.