Image Number 5 for United States Patent #4794389.
Attribute hierarchy system including hardware assisted by software for utilizing a stack structure of a multiple-level stack and a plurality of stacks for storing data and attributes. The stack structure provides that only the top of the stack is loaded and utilized. The software controls the hardware logic flow associated with the stack and the stacks. The hardware includes an attribute memory and character data storage, a character data counter and position register. An attribute mask and attribute processor control loading of the attributes. A command register pushes, pops or loads to the stacks along with a sequence controller input from the attribute processor. A command decoder determines sequence of operation for loading attributes and character into row buffers. A stack control flags when a valid load has occurred, and if no load occurred, the stack defaults and a copy operation occurs.