LM1246AAA National Semiconductor, LM1246AAA Datasheet - Page 26

• Manufacturer Part Number: LM1246AAA
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM/ 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

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Microcontroller Interface
LM1246 Address Map
CHARACTER ROM
The 512 font characters from 0x0000 to 0x7FFF can be read from ROM by addressing the individual pixel rows of the desired
character. Since the characters have 12 columns, it takes two bytes to read a given row of pixels within one character. Since the
characters have 18 rows, a total of 36 bytes are needed to read the entire character. The 16-bit address for reading a row of pixels
is formed as follows:
Note that bit 0 of the Character Font Access Register, 0x8402, needs to be set to 0 to read the 2-color fonts. In order to read the
four-color fonts, two complete reads are needed. Set bit 0 of the Character Font Access Register, 0x8402, to a 0 to read the least
significant plane and to a 1 to read the most significant plane. See Table 4. Character ROM Addressing.
where: N = bank number (0x0 ≤ N ≤ 0x7)
I = Character Index within its respective bank (0x00 ≤ I ≤ 0x3F)
R = row of pixels within the character (0x00 ≤ R ≤ 0x11)
H = 0 for low byte, 1 for high byte
Address = (N * 0x1000) + (I * 0x40) + (R * 0x02) + H
FIGURE 25. I
FIGURE 26. I
(Continued)
2
2
C Compatible Write Sequence
C Compatible Read Sequence
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