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Motorola 6845

Motorola 6845 CRT controller

The Motorola 6845, or MC6845, is a display controller that was widely used in 8-bit computers during the 1980s.[1][2] Originally intended for designs based on the Motorola 6800 CPU and given a related part number, it was more widely used alongside various other processors, and was most commonly found in machines based on the Zilog Z80 and MOS 6502.

The 6845 is not an entire display solution on its own; the chip's main function is to properly time access to the display memory, and to calculate the memory address of the next portion to be drawn. Other circuitry in the machine then uses the address provided by the 6845 to fetch the pattern and then draw it. The implementation of that hardware is entirely up to the designer and varied widely among machines. The 6845 is intended for character displays, but could also be used for pixel-based graphics, with some clever programming.

Among its better-known uses are the BBC Micro, Amstrad CPC, and Videx VideoTerm display cards for the Apple II.[1] It is also part of many early graphics adapter cards for the IBM PC, including the MDA, Hercules Graphics Card (HGC), Color Graphics Adapter (CGA) and the Plantronics Colorplus.[3] Its functionality was duplicated and extended by custom circuits in the EGA and VGA PC video adapters.

  1. ^ a b "The 6845 Cathode Ray Tube Controller (CRTC)". www.tinyvga.com. Retrieved 2022-11-18.
  2. ^ "Differences of CRTC models". www.6502.org. Retrieved 2022-11-18.
  3. ^ PC Mag Jul 1983, p. 435, at Google Books

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