Epson S1D13504 manual Panning and Scrolling

Epson Research and Development	Page 25
Vancouver Design Center

4.Program the Memory Address Offset Registers. Register [17h] will be set to 0 and register [16h] will be set to 0xA0.

4.2Panning and Scrolling

Panning and scrolling are typically used to navigate within an image which is too large to be shown completely on the display device. Although the image is stored entirely in display buffer, only a portion is actually visible at any given time.

Panning and scrolling refers to the direction the viewport appears to move. Panning describes the action where the viewport moves horizontally. When panning to the right the image in the viewport appears to slide to the left. A pan to the left causes the image to appear as if it’s sliding to the right. Scrolling describes the up and down motion of the viewport. Scrolling down causes the image to appear to slide upwards and scrolling up results in an image that appears to slide downwards.

On the S1D13504 panning is performed by setting two components: the start address registers provide a word granularity in movement (more than one pixel) while the pixel panning register allows panning at the pixel level. Scrolling requires changing only the start address registers.

There is an order these registers should be accessed to provide the smoothest apparent movement possible. Understanding the sequence of operations performed by the S1D13504 will make it apparent why the order should be followed.

The start address is latched at the beginning of each frame, the pixel panning value is latched immediately upon being set. Setting the registers in the wrong sequence or at the wrong time will result in a “tearing” or jitter on the display. The correct sequence for programing these registers is:

1.Wait until just after a vertical non-display period (read register [0Ah] and watch bit 7 for the non-display status).

2.Update the start address registers.

3.Wait until the next vertical non-display period.

4.Update the pixel paning register.

Note

The S1D13504 provides a false indication of vertical non-display period when used with a dual panel display. In this case it is impossible to identify the false signal from the true non-display period. The result is that panning operations at less than 15 bpp may exhibit an occasional tear as the result of updating registers in the wrong order. This effect is barely noticeable at 8 bpp but becomes pronounced at 4 bpp, and lower, color depths. Setting the registers out of sequence will make the tear more apparent.

Programming Notes and Examples	S1D13504
Issue Date: 01/02/01	X19A-G-002-07