Random Access Memory Digital-to-Analog Converter
<hardware>
(RAMDAC) A combination of three fastDACs with asmallSRAM used in graphicsdisplay adapters to store thecolour palette and to generate the analog signals to drive acolourmonitor. The logical colour number from the displaymemory is fed into the address inputs of the SRAM to select apalette entry to appear on the output of the SRAM. This entryis composed of three separate values corresponding to thethree components (red, green, and blue) of the desiredphysical colour. Each component value is fed to a separateDAC, whose analog output goes to the monitor, and ultimatelyto one of its threeelectron guns (or equivalent innon-CRT displays).
DAC word lengths range usually from 6 to 10 bits. The SRAM'swordlength is three times the DAC's word length. The SRAMacts as acolour lookup table. It usually has 256 entries(and thus an 8-bit address). If the DAC's word length is also8 bits, we have a 256 x 24-bit SRAM which allows a selectionof 256 out of 16777216 possible colours for the display. Thecontents of the SRAM can be changed while the display is notactive (duringdisplay blanking times). The SRAM canusually be bypassed and the DACs can be fed directly bydisplay data (fortrue colour modes).Last updated:1996-03-24
Nearby terms:
Random Access Memory Digital-to-Analog Converter ♦randomness
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