LM1247 National Semiconductor, LM1247 Datasheet - Page 23

• 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

LM1247 Address Map
DISPLAY PAGE RAM
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 behaviour. NOTE: To avoid any unpredictable
behaviour, 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 12 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. The type of code is determined by the write
sequence, which must conform to the allowable sequences shown in Table 6. To simplify the table, CC represents one or more
character codes in sequence. A single write operation is enclosed in brackets [], and the both bytes of the Page Ram Address are
shown as one symbol, ADDR.
When reading characters from RAM, bit 1 of the Character Font Access Register (0x8402) determines whether the character
code or its attribute code is returned. Table 7 gives the character code format read when bit 1 of the Character Font Access
Register is a 0. Table 8 gives the attribute format read when this bit is set to a 1.
RAM DATA FORMAT
Each of the 512 locations in the page RAM is comprised of a 12-bit code consisting of an 8-bit character or control code, and a
4-bit attribute code. Each of the characters are stored in sequence in the page RAM in bits 7:0. Special codes are used between
lines to show where one line ends and the next begins, and also to allow blank (or “skipped”) single scan lines to be added
between character lines. Table 9 shows the format of a character stored in RAM. Note that even though this is a 12 bit format,
reading and writing characters and codes is done in 8 bytes.
One Line of Characters Only.
One Line of Characters with Attribute Change.
Two Lines of Characters with one Attribute.
Two Lines of Characters Separated with Skip Line.
Two Lines of Characters, each with its own Attribute.
Changing a Character String in a Displayed Screen.
Changing Only an Attribute in a Displayed Screen.
Fonts - 2 Color
Fonts - 4 Color
Fonts - 2 Color
Fonts - 4 Color
Register
Address Range
0x8000–0x81FF
0x8000–0x81FF
OSD Image Consists of
Address
(Continued)
0x0000–0x2FFE
0x3000–0x3FFE
0x4000–0x6FFE
0x7000–0x7FFE
TABLE 7. Page RAM Character Read Data
TABLE 8. Page RAM Attribute Read Data
TABLE 6. Page RAM Write Sequences
TABLE 5. Character ROM Read Data
Address
+1
+1
+1
+1
D7
D7
x
D6
D6
x
23
[ADDR-AC-SL-CC-EOS]
[ADDR-AC-SL-CC] [ADDR-AC-CC-EOS]
[ADDR-AC-SL-CC-EOL-SL-CC-EOS]
[ADDR-AC-SL-CC-EOL-AC-SL-EOL-AC-SL-CC-EOS]
[ADDR-AC-SL-CC-EOL] [ADDR-AC-SL-CC-EOS]
[ADDR-AC-CC]
[ADDR-CC] (CC is the currently displayed character)
D7
X
X
X
X
D5
D5
x
D6
CHAR_CODE[7:0]
X
X
X
X
D4
D4
x
D5
X
X
X
X
Write Sequence(s)
D3
D3
PIXEL[7:0]
PIXEL[7:0]
PIXEL[7:0]
PIXEL[7:0]
D4
X
X
X
X
ATTR_CODE[3:0]
D2
D2
D3
PIXEL[11:8]
PIXEL[11:8]
PIXEL[11:8]
PIXEL[11:8]
D2
D1
D1
D1
www.national.com
D0
D0
D0