LM1247 National Semiconductor, LM1247 Datasheet - Page 22

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

www.national.com
Microcontroller Interface
LM1247 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 follow:
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.
When read back, the low byte will contain the first eight pixels of the row with data bit 0 corresponding to the left most bit in the
pixel row. The high byte will contain the remaining four pixels in the least significant nibble. The remaining 4 bits, shown as “X”,
are “don’t care” bits, and should be discarded. Bit 3 of the high byte corresponds to the right most pixel in the pixel row. This is
shown in Table 5.
Address Range
0x0000–0x2FFF
0x3000–0x3FFF
0x4000–0x6FFF
0x7000–0x7FFF
R/W
R
R
R
R
where: N = bank number (0x0 ≤ N ≤ 0x7)
These are the first 3 banks of two-color, read-only ROM character
fonts. There are 192 total characters in this range.
This is bank 3 of four-color, read-only ROM character fonts. There
are 64 total characters in this range.
These are banks 4, 5 and 6 of two-color read-only ROM character
fonts. There are 192 characters in this range.
This is bank 7 of four-color, read-only ROM character fonts. There
are 64 total characters in this range.
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
FIGURE 24. I
TABLE 4. Character ROM Addressing
(Continued)
*
0x1000) + (I
2
C Compatible Read Sequence
Description
22
*
0x40) + (R
*
0x02) + H
0x8402[0]
0/1
0/1
0
0
20048439
0x0
0x1
0x2
0x3
0x4
0x5
0x6
0x7
N