Epson S1D13705 technical manual Panning and Scrolling

Epson Research and Development	Page 27
Vancouver Design Center

Example 2: From the above, what is the maximum number of lines our image can contain?

Step 1: Calculate the number of bytes on each line.

bytes_per_line = pixels_per_line / pixels_per_byte = 640 / 4 = 160

Each line of the display requires 160 bytes.

Step 2: Calculate the number of lines the S1D13705 is capable of.

total_lines = memory / bytes_per_line = 81920 / 160 = 512

We can display a maximum of 512 lines. Our example image requires 480 lines so this example can be done.

5.2 Panning and Scrolling

Panning and scrolling describe the operation of moving a physical display viewport about a virtual image in order to view the entire image a portion at time. For example, after setting up the previous example (virtual display) and drawing an image into it we would only be able to view one quarter of the image. Panning and scrolling are used to reveal the rest of the image.

Panning describes the horizontal (side to side) motion of the viewport. When panning to the right the image in the viewport appears to slide to the left. When panning to the left the image to appears to slide to the right. Scrolling describes the vertical (up and down) motion of the viewport. Scrolling down causes the image to appear to slide up and scrolling up causes the image to appear to slide down.

Both panning and scrolling are performed by modifying the start address register. The start address registers in the S1D13705 are a word offset to the data to be displayed in the top left corner of a frame. Changing the start address by one means a change on the display of the number of pixels in one word. The number of pixels in word varies according to the color depth. At 1 bit-per-pixel a word contains sixteen pixels. At 2 bit-per-pixel there are eight pixels, at 4 bit-per-pixel there are four pixels and at 8 bit-per-pixel there is two pixels in each word. The number of pixels in each word represent the finest step we can pan to the left or right.

When portrait mode (see Hardware Rotation on page 37) is enabled the start address registers become offsets to bytes. In this mode the step rate for the start address registers if halved making for smoother panning.

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