Epson S1D13705 technical manual To scroll down

Page 30	Epson Research and Development
	Vancouver Design Center

Example 4: Scrolling (Up and Down)

To scroll down, increase the value in the Screen 1 Display Start Address Register by the number of words in one virtual scan line. To scroll up, decrease the value in the Screen 1 Display Start Address Register by the number of words in one virtual scan line. A virtual scan line includes both the number of bytes required by the physical display and any extra bytes that may be being used for creating a virtual width on the display.

The previous dimensions are still in effect for this example (i.e. 320w x 240h virtual size, 256h x 64w physical size at 4 bpp)

Step 1: Determine the number of words in one virtual scanline.

bytes_per_line = pixels_per_line / pixels_per_byte = 320 / 2 = 160

words_per_line = bytes_per_line / 2 = 160 /2 = 80

Step 2: Scroll up or down

To scroll up.

StartWord = GetStartAddress(); StartWord -= words_per_line; if (StartWord < 0)

StartWord = 0;

SetStartAddress(StartWord);

To scroll down.

StartWord = GetStartAddress();

StartWord += words_per_line;

SetStartAddress(StartWord);

}

S1D13705	Programming Notes and Examples
X27A-G-002-03	Issue Date: 02/01/22