System RAM must be allocated for the display system when the display system is running and unblanked. One portion of system RAM is called the frame buffer. In text modes, the frame buffer is used for storing the characters to be displayed. In graphics modes, the frame buffer is used for storing the pixel values. Another portion of system RAM, called the font buffer, must be allocated when using text modes. It is used to define the pixel information of characters in the current character set.
The display controller is the portion that resides on the Hornet chip. Its function is to format the information in system RAM and generate the waveforms to display that information on the display module. It may be divided into temporary storage buffers, control registers, processing modules, and the display interface. The temporary storage buffers are transparent to programming. They are used to reduce the system performance impact of using system RAM for the frame buffer and font buffer . The control registers are used by software to control the format of the display. The function of the various processing modules will be described by describing the registers that control them.
