The MC6847 is a video display generator chip that is designed for the 6800 family of microprocessors. It reads data from memory (via the SAM chip) and displays the contents on screen. The 6847 is used on Coco 1 and 2's only; this function was replaced by the custom GIME chip in Coco 3 models.
The chip provides a 32×16 alphanumeric display, or graphic displays up to 256×192 pixels in resolution. Additionally, a variety of "semigraphics" modes are provided.
On the Coco, the familiar dark-green on light-green text is generated as a fundamental function of this chip.
In Coco 1's and most Coco 2's, the 6847 is not capable of displaying lowercase. Instead, lower case text appears inverted. Later Coco 2's replaced the 6847 with a 6847T1 that can display proper lower case text.
- Wikipedia article on the Motorola 6847
- Datasheet http://instruct1.cit.cornell.edu/courses/ee476/ideas/mc6847.pdf