P.33
The hardware cursor replaces the software mouse cursor and eliminates to store and restore the
screen data as changed the mouse position. Typically, the application software initializes the cursor
once and only needs to update the screen position by setting registers. So we can provide a smooth-
moving mouse pointer by compared with a software mouse.
PC Video Controller
TP6508 allows up to 24-bit of external RGB video data to be input and merged with the internal
VGA data stream. The TP6508 can support two forms of video window: 1) color key input and 2) X-
Y window keying. The X-Y window key input can be used to position the live video window coordi-
nates.
LCD Line Buffer
For dual-scan STN LCD panels, those panels require the upper and lower panels to refresh
simultaneously so that we need additional buffer and logic to implement. The additional buffer is
called "LCD frame buffer" storing the STN LCD's refresh data which are half of a whole LCD panel's.
In TP6508 we have three frame-buffer technique; shadow frame buffer, external frame buffer, pseudo
frame buffer, to accelerate LCD display refresh.
For shadow frame buffer, we can share the off-screen display memory as the LCD frame buffer by
programming the upper display memory region. TP6508 also implements a LCD Line buffer to process
and store a line of the LCD refresh data at the start of every CRT horizontal raster. The operation
sequence of LCD line buffer is executed by the following steps:
1. Read a line of LCD frame data which are used for the present display frame from shadow
frame buffer during the horizontal blank cycle.
2. Write a line of LCD frame data which are used for the next display frame to shadow
frame buffer by following the step-1 during the horizontal blank cycle.
3. Output to panel controller from LCD line buffer, a set of frame information of pixels which
are read from shadow frame buffer are used to display one of the half LCD panel.
4. Generate and store into LCD line buffer from panel controller, a set of the frame information
of pixels which will write to shadow frame buffer are used to display another of the half
LCD panel for next frame.
5. Continuously, process the step-3 and step-4 until ending a line of LCD frame data during the
horizontal display period.
6. Restart from step-1 for next horizontal raster display and repeat for whole frame display
refresh.
VGA has the memory bandwidth limitation, but CRT refresh rate higher than memory fetch speed.
By external frame buffer technique, we can add another external 256Kx16-bit DRAM-C as a LCD
frame buffer. The video-in and pin[8:15] of Panel is also by DRAM-C interface.
In addition, the another solution for dual-scan STN LCD panel display is used the pseudo frame
buffer technique. It is no additional memory required, but it gets rather lower LCD display contrast
than others. It is designed to optimize cost and quality trade-off considerations.