
5 ADVANCED TECHNIQUES
C-2-20
EPSON
SID13705 PROGRAMMING NOTES
AND EXAMPLES
5.3 Split Screen
Occasionally the need arises to display two different but related images. Take, for example, a
game where the main play area requires rapid updates and game status, displayed at the bottom of
the screen, requires infrequent updates.
The Split Screen feature of the SID13705 block allows a programmer to setup a display in such a
manor. When correctly configured the programmer has only to update the main area on a regular
basis. Occasionally, as the need arises, the secondary area is updated.
The figure below illustrates how a 320
×240 panel may be configured to have one image displaying
from scan line 0 to scan line 199 and image 2 displaying from scan line 200 to scan line 239.
Although this example picks specific values, the split between image 1 and image 2 may occur at
any line of the display.
Figure 5-2 320
×240 Single Panel For Split Screen
In split screen operation “Image 1” is taken from the display memory location pointed to by the
Screen 1 Start Address registers and is always located at the top of the screen. “Image 2” is taken
from the display memory location pointed to by the Screen 2 Start Address registers. The line
where “Image 1” end and “Image 2” begins is determined by the Screen 1 Vertical Size register.
Registers
Split screen operation is performed primarily by manipulating three register sets. Screen 1 Start
Address and Screen 2 Start Address determine from where in display memory the first and second
images will be taken from. The Vertical Size registers determine how many lines Screen 1 will
use. The following is a description of the registers used to do split screen.
Screen 1 Vertical Size
These two registers form a ten bit value which determines the size of screen 1. When the vertical
size is equal to or greater than the physical number of lines being displayed there is no visible
effect on the display. When the vertical size value is less than the number of physical display lines,
operation is like this:
1. From the beginning of a frame to the number of lines indicated by vertical size the display data
will come from the memory area pointed to by the Screen 1 Display Start Address.
Scan Line 0
Image 1
...
Scan Line 199
Scan Line 200
Image 2
...
Scan Line 239
Screen 1 Vertical Size Registers = 199 lines
REG[13] Screen 1 Vertical Size (LSB)
Bit 7Bit 6Bit 5Bit 4
Bit 3Bit 2Bit 1Bit 0
REG[14] Screen 1 Vertical Size (MSB)
n/a
Bit 9
Bit 8