SED1374 Datasheet, PDF (123/420 Pages) Epson Company – SED1374 Embedded Memory Color LCD Controller

Epson Research and Development
Vancouver Design Center
Page 27
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 SED1374 is capable of.
total_lines = memory / bytes_per_line = 40960 / 160 = 256
The the maximum number of lines which can be accommodated by our image can contain
is 256. This example will not “fit” in available display memory. We must reduce either the
color depth or the virtual image size.
5.2 Panning and Scrolling
Panning and scrolling describe the actions of appearing to move the image in a virtual
display so that all the image can be viewed. After correctly setting up a virtual display (see
above) and loading an image into display memory, panning and scrolling allow viewing the
entire image a portion at a time.
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. Start
address refers to the word offset in the display buffer where the image will start being
displayed from. The start address registers in the SED1374 are an offset to the first word to
be displayed in the top left corner of every frame.
Keep in mind that the start address is a word offset. Changing the start address by one
means a change of one words worth of pixels. 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
are two pixels. The number of pixels in each word represent the finest panning step the
SED1374 is capable of. (i.e. at 4 bit-per-pixel the display will move sideways by four pixels
for each change to the start address registers)
When SwivelView mode (see SwivelView™ on page 36) 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
Issue Date: 99/04/27
SED1374
X26A-G-002-02