Epson S1D13705 technical manual Alternate Portrait Mode

Epson Research and Development	Page 39
Vancouver Design Center

7.3 Alternate Portrait Mode

Alternate portrait mode does not impose the power of two line width. To rotated the image on 240 line panel requires a portrait stride of 240 pixels. Alternate portrait mode is capable of scrolling by one line at a time in response to changes to the Start Address Registers.

However, to achieve the same frame rate requires a 2 x faster input clock, therefore using more power.

The following figure depicts the ways to envision memory layouts for the S1D13705 in alternate portrait mode. This example also uses a 320x240 panel. Notice that in alternate portrait mode the stride may be as little as 240 pixels.

physical memory start address

480

A B

portrait window

C D

320

image seen by programmer = image in display buffer

		B	window	D	320
display		portrait
start
address
	A			C
		480

image refreshed by S1D13705

Figure 7-2: Relationship Between the Alternate Mode Screen Image and the Image Refreshed by S1D13705

From the programmers perspective the memory is laid out as shown on the left. The programmer accesses memory exactly as for a panel of with the dimensions of 240x320. The programmer sees memory addresses increasing from A->B and from B->C.

From a hardware perspective the S1D13705 always refreshes the LCD panel in the order B->D and down to do A->C

The greatest factor in selecting alternate portrait mode over default portrait mode would be for the ability to obtain an area of contiguous off screen memory. For example: A 640x480 panel in default portrait mode at two bit-per-pixel requires 81920 bytes (80 Kb). There is unused memory but it is not contiguous. The same situation using alternate portrait mode requires 76800 bytes leaving 5120 bytes of contiguous memory available to the application. In fact the change in memory usage may make the difference between being able to run certain panels in portrait mode or not being able to do so.

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