Epson S1D13705 - Manual (Page 133)

Epson Research and Development Page 39
Vancouver Design Center
Programming Notes and Examples S1D13705
Issue Date: 02/01/22 X27A-G-002-03
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.
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.
image seen by programmer
= image in display buffer
480
portrait
window
480
320
A B
C D
D
C
B
A
320 start
address po
rt
rai
t
w
ind
ow display
image refreshed by S1D13705
start
address
physical
memory