
7 HARDWARE ROTATION
SID13705 PROGRAMMING NOTES
EPSON
C-2-25
AND EXAMPLES
7
HARDWARE ROTATION
7.1 Introduction To Hardware Rotation
Many of todays applications use the LCD panel in a portrait orientation (typically LCD panels are
landscape oriented) . In this case it becomes necessary to “rotate” the displayed image. This
rotation can be done by software at the expense of performance or, as with the SID13705 block, it
can be done by hardware with no performance penalty.
This discussion of display rotation is intended to augment the excellent description of the
hardware functionality found in the Hardware Functional Specification.
The SID13705 block supports two portrait modes: Default Portrait Mode and Alternate Portrait
Mode.
7.2 Default Portrait Mode
Default portrait mode was designed to reduce power consumption for portrait mode use. The
reduced power consumption comes with certain trade offs.
The most obvious difference between the two modes is that Default Portrait Mode requires the
portrait width be a power of two, e.g. a 240-line panel, used in portrait mode, requires setting a
virtual width of 256 pixels. Also default portrait mode is only capable of scrolling the display in
two line increments.
The benefits to using default portrait mode lies in the ability to use a slower input clock and in
reduced power consumption.
The following figure depicts the ways to envision memory layouts for the SID13705 block in
default portrait mode. This example uses a 320
× 240 panel.
Figure 7-1 Relationship Between the Default Mode Screen Image and the Image Refreshed by SID13705 block
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 240
× 320 setup to have a 256
pixel horizontal stride. The programmer sees memory addresses increasing from A->B and from C-
>D.
From a hardware perspective the SID13705 block always refreshes the LCD panel in the order B-
>D and down to do A->C.
256
25
6
image seen by programmer
= image in display buffer
320
portrait
window
32
0
240
AB
C
D
C
B
A
24
0
start
address
po
rtr
a
it
w
ind
ow
display
E
image refreshed by SID13705 block
start
address
physical
memory