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LM1246 Address Map
(Continued)
TABLE 4. Character ROM Addressing
Address Range
0x0000–0x2FFF
R/W
R
Description
0x8402[0]
0
N
These are the first 3 banks of two-color, read-only ROM character
fonts. There are 192 total characters in this range.
0x0
0x1
0x2
0x3
0x3000–0x3FFF
R
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.
0/1
0x4000–0x6FFF
R
0
0x4
0x5
0x6
0x7
0x7000–0x7FFF
R
This is bank 7 of four-color, read-only ROM character fonts. There
are 64 total characters in this range.
0/1
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
.
TABLE 5. Character ROM Read Data
Register
Fonts - 2 Color
Address
0x0000–0x2FFE
+1
0x3000–0x3FFE
+1
0x4000–0x6FFE
+1
0x7000–0x7FFE
+1
D7
D6
D5
D4
PIXEL[7:0]
X
PIXEL[7:0]
X
PIXEL[7:0]
X
PIXEL[7:0]
X
D3
D2
D1
D0
X
X
X
PIXEL[11:8]
Fonts - 4 Color
X
X
X
PIXEL[11:8]
Fonts - 2 Color
X
X
X
PIXEL[11:8]
Fonts - 4 Color
X
X
X
PIXEL[11:8]
CHAR_CODE[3:0] or
ATTR_CODE
Display Page
0x8000–0x83FF
X
CHAR_CODE[7:4] or
reserved
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.
TABLE 6. Page RAM Lower Byte Read Data
Address Range
0x8000–0x81FF
D7
D6
D5
D4
D3
D2
D1
D0
CHAR_CODE[7:0]
TABLE 7. Page RAM Upper Byte Read Data
Address
0x8000–0x81FF
D7
X
D6
X
D5
X
D4
CC[8]
D3
D2
D1
D0
ATTR_CODE[3:0]
L
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