VIDC1

The VIDC1 was a Video Display Controller chip created as an accompanying chip to the ARM CPU as used in Acorn Archimedes computer systems, its successor the VIDC20 was used in the later RiscPCs.^[1]

Video[]

The VIDC1 offers colour depths of 1, 2, 4 or eight bits per colour, offering 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]

Sound[]

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

References[]