LM1253A National Semiconductor, LM1253A Datasheet - Page 32

• Manufacturer Part Number: LM1253A
• Description: Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator
• Manufacturer: National Semiconductor

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ATT4C3n
ATT4C4n
ATT4C5n
ATT4C6n
ATT4C7n
Register
Four-Color Attribute Table
Note: Set Reserved bits to 0.
Four-color display character Attribute Table. The attributes for four-color display characters may be written or read via the follow-
ing address format:
A15–A7: Always 1000_0101_0b
A6–A3: Attribute value (0h–Fh are valid values), n
A2–A0: Determine which of the six bytes of the attribute is to be accessed.
NOTE: In the table, n indicates the attribute number, 0
NOTE: When writing, bytes 0 to 2 must be written, in that order and bytes 4 to 6 must be written, in that order.
Bytes 0 through 2 will take effect after byte 2 is written. Bytes 4 through 6 will take effect after byte 6 is written.
Since bytes 5 and 7 contain all reserved bits, these bytes may be written, but no effect will result. When reading, it is OK to read
only one, two, or all three bytes.
If writing more than one 4-color attributes using the auto increment feature, all eight bytes must be written.
Display Page RAM
The OSD Window
The Display Page RAM contains all of the 8 bit display character codes and their associated 4 bit attribute codes, and the special
12 bit page control codes — the row-end, skip-line parameters and window-end characters.
The LM1253A has a distinct advantage over many OSD generators that it allows variable size and format windows. The window
size is not dictated by a fixed geometry area of RAM. Instead, 512 locations of 12 bit words are allocated in RAM for the definition
of the windows, with special control codes to define the window size and shape.
Window width can be any length supported by the number of pixels per line that is selected divided by the number of pixels in a
character line. It must be remembered that OSD characters displayed during the monitor blanking time will not be displayed on
the screen, so the practical limit to the number of horizontal characters on a line is reduced by the number of characters within
the horizontal blanking period.
Character Code And Attribute Code
Each of the 512 x 12 bit locations in the page RAM is comprised of an 8 bit character or control code, and a 4 bit attribute code:
Bits 11–4 Character Code: These 8 bits define which of the 254 characters is to be called from the character ROM. Valid char-
Bits 3–0:
Each of the characters are stored in sequence in the page RAM. Special codes are used between lines to show where one line
ends and the next begins, and also to allow blank (or ‘skipped’) lines to be added between character rows.
acter codes are 02h–FFh.
Attribute code. These 4 bits address the attribute table used to specify which of the 16 locations in RAM specify the
colors and enhanced features to be used for this particular character. Two separate attribute tables are used, one for
2-color characters, the other for 4-color characters.
Address
+3
+4
+5
+6
+7
C4B[0]
D7
X
X
X
C3B[1:0]
TABLE 8. Four-Color Attribute Registers (Continued)
LM1253A Four-Color Attribute Registers
D6
X
X
X
(Continued)
C4G[2:0]
<
D5
=n
X
X
X
<
=15
32
C3G[2:0]
D4
X
X
X
D3
X
X
X
C4R[2:0]
D2
X
X
X
C3R[2:0]
D1
X
X
DS101265-47
C4B[2:1]
C3B[2]
D0
X
X