SED1354 Datasheet, PDF (169/472 Pages) Epson Company – Color Graphics LCD/CRT Controller

Epson Research and Development
Vancouver Design Center
Page 29
REG[13h] Screen 2 Display Start Address Register 0
Start Address Start Address Start Address Start Address Start Address Start Address Start Address Start Address
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
REG[14h] Screen 2 Display Start Address Register 1
Start Address Start Address Start Address Start Address Start Address Start Address Start Address Start Address
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
REG[15h] Screen 2 Display Start Address Register 2
n/a
n/a
n/a
n/a
Start Address Start Address Start Address Start Address
Bit 19
Bit 18
Bit 17
Bit 16
These three registers form the twenty bit offset to the first word in display buffer that will be shown
in the screen 2 portion of the display.
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 locat-
ed 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 immedi-
ately (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 * 480 = 19,200 words = 0x4B00 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 0x00, 0x4B
and 0x00 respectively.
Programming Notes and Examples
Issue Date: 98/10/28
SED1354
X19A-G-002-06