LM1246AAA National Semiconductor, LM1246AAA Datasheet - Page 27

• 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

LM1246 Address Map
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. Character ROM Read Data.
DISPLAY PAGE RAM
Standard 1247 Mode
This address range (0x8000–0x81FF) contains the 512 characters, which comprise the displayable OSD screens. There must be
at least one End-Of-Screen code (0x00) in this range to prevent unpredictable behavior. NOTE: To avoid any unpredictable
behavior, this range should be cleared by writing a 0 to bit 3 of the FRMCTRL1 Register, 0x8400, immediately after power up.
There may also be one or more pairs of End-Of-Line and Skip Line codes. The codes and characters are written as 8-bit bytes,
but are stored with their attributes in groups of 13 bits. When writing, one byte describes a displayed character (CC), Attribute
Code (AC), End-Of-Screen (EOS), End-Of-Line (EOL) or Skip Line (SL) code.
Full 512 Displayable Character Mode
This mode differs from the above in that the character code is 9 bits long; the attribute code is still 4 bits long, and so the 13-bit
wide Page RAM of the LM1246 is fully utilized. The codes and characters are still written as 8-bit bytes, but are stored with their
attributes in groups of 13 bits.
When reading characters from RAM, bit 1 of the Character Font Access Register (0x8402) determines whether the lower 8 bits
or upper 5 bits of the Page RAM are returned. Table 6. Page RAM Lower Byte Read Data gives the lower byte read, which is the
first 8 character code bits when bit 1 of the Character Font Access Register is a 0. Table 7. Page RAM Upper Byte Read Data
gives the upper byte read, which is the 9th character code bit and 4 attribute code bits when this bit is set to a 1.
Address Range
0x0000–0x2FFF
0x3000–0x3FFF
0x4000–0x6FFF
0x7000–0x7FFF
Fonts - 2 Color
Fonts - 4 Color
Fonts - 2 Color
Fonts - 4 Color
Display Page
Register
Address Range
0x8000–0x81FF
0x8000–0x81FF
Address
R/W
R
R
R
R
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.
(Continued)
0x0000–0x2FFE
0x3000–0x3FFE
0x4000–0x6FFE
0x7000–0x7FFE
0x8000–0x83FF
TABLE 6. Page RAM Lower Byte Read Data
TABLE 7. Page RAM Upper Byte Read Data
Address
TABLE 4. Character ROM Addressing
TABLE 5. Character ROM Read Data
+1
+1
+1
+1
D7
D7
X
D6
D6
X
Description
27
D7
X
X
X
X
X
D5
D5
X
CHAR_CODE[7:4] or
D6
X
X
X
X
CHAR_CODE[7:0]
CC[8]
D4
D4
reserved
D5
X
X
X
X
D3
D3
D4
PIXEL[7:0]
PIXEL[7:0]
PIXEL[7:0]
PIXEL[7:0]
X
X
X
X
ATTR_CODE[3:0]
D3
D2
D2
CHAR_CODE[3:0] or
0x8402[0]
ATTR_CODE
PIXEL[11:8]
PIXEL[11:8]
PIXEL[11:8]
PIXEL[11:8]
D2
0/1
0/1
0
0
D1
D1
www.national.com
D1
D0
D0
0x0
0x1
0x2
0x3
0x4
0x5
0x6
0x7
N
D0