Epson S1D13504 manual REG13h Screen 2 Display Start Address Register

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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	S1D13504
Issue Date: 01/02/01	X19A-G-002-07