A display adaptor has an overlay feature where an overlay image is mapped over the active image as long as the overlay image area is smaller than the active image area. The system neither requires any...

A display adaptor has an overlay feature where an overlay image is mapped over the active image as long as the overlay image area is smaller than the active image area. The system neither requires any blanking space nor needs a dual buffering scheme. Assume the pixels in the image and overlay buffers are not separated into RGB components, but rather integrated into single pixels when they are taken out of these buffers to feed the frame. There is a certain synchronization mechanism between the image and the overlay address counters, and also between the pixel and line counters. As soon as a pixel is fetched from the image or overlay buffer, it is placed in the display frame with the aid of the pixel and the line counter. There are no write-enable controls for the buffers as these buffers will not be replenished with new pixels once exhausted. The image is displayed only once. The read-enables for both buffers are also kept at logic 1 until the buffers are empty. Therefore, the only mechanism that aids the pixels out of these buffers and moves them to the display frame is incrementing the address counters and switching the selector inputs at the 2-1 buffer MUX. After removing the external reset, the operation of the display unit starts as shown in the timing diagram.

(a) Build the register file. Indicate the programmable values in each register to support the operation of this unit.

(b) Fill in each blank space that corresponds to the numbers in the timing diagram (if there are no numbers, ignore the entries), and complete the control signals, selImage (to select the image buffer), selOL (to select the overlay buffer), IncrPix (to increment the pixel counter), ResetPix (to reset the pixel counter to 0), IncrLine (to increment the line counter) and IncrOL (to increment the overlay counter). Use the following notation to represent the data when retrieving them from the data buffers: For the Image buffer, Data = IM [Image Buffer Address] For the Overlay buffer, Data = OL [OL Buffer Address]