User`s manual

4: ADVANCED TECHNIQUES
S1D13504 PROGRAMMING NOTES EPSON 2-19
AND EXAMPLES (S19A-G-002-06)
Screen 1 memory is always the first memory displayed at the top of the screen followed by screen 2
memory. However, the start address for the screen 2 image may in fact be lower in memory than that
of screen 1 (i.e. screen 2 could be coming from offset 0 in the display buffer while screen 1 was
coming from an offset located several thousand bytes into display buffer). While not particularly
useful, it is possible to set screen 1 and screen 2 to the same address.
4.3.2 Examples
Example 7
Display 380 scanlines of image 1 and 100 scanlines of image 2. Image 2 is located
immediately after image 1 in the display buffer. Assume a 640x480 display and a
color depth of 1 bpp.
1. The value for the line compare is not dependent on any other setting so we can set it immediately
(380 = 0x17C).
Write the line compare registers [0Fh] with 0x01 and register [0Eh] with 0x7C.
2. Screen 1 is coming from offset 0 in the display buffer. Although not necessary, ensure that the
screen 1 start address is set to zero.
Write 0x00 to registers [10h], [11h] and [12h].
3. Calculate the size of the screen 1 image (so we know where the screen 2 image is located). This
calculation must be performed on the virtual size (offset register). Since a virtual size was not
specified assume the virtual size to be the same as the physical size.
offset = pixels_per_line / pixels_per_word = 640 / 16 = 40 words per line
screen1_size = offset * lines = 40 * 380 = 15,200 words = 0x3B60 words
4. Set the screen 2 start address to the value we just calculated.
Write the screen 2 start address registers [13h], [14h] and [15h] with the values 0x60, 0x3B and
0x00 respectively.