LM1246 Datasheet, PDF (32/51 Pages) National Semiconductor (TI) – 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs

Building Display Pages (Continued)
always contain the Skip-Line (SL) code associated with the
first line of Display Window 1. The attribute for this SL code
must be written before the SL code itself, and will be stored
in the lower four bits of this memory location. Subsequent
locations should contain the characters to be displayed on
line 1 of Display Window 1, until the EOL code or EOS code
is written into the Display Page-RAM.
The Skip-Line parameters associated with the next line must
always be written to the location immediately after the pre-
ceding line’s End-Of-Line character. The only exception to
this rule is when an End-Of-Screen character (value 0x0000)
is encountered. It is important to note that an End-Of-Line
character should not precede an End-Of-Screen character
(otherwise the End-Of-Screen character will be interpreted
as the next line’s Skip-Line code). Instead, the End-Of-
Screen code will end the line and also end the window,
making it unnecessary to precede it with a EOL. The I²C
Format for writing a sequence of display characters is mini-
mized by allowing sequential characters with the same at-
tribute code to send in a string as follows:
Byte #1: I²C Slave Address
Byte #2: LSB Register Address
Byte #3: MSB Register Address
Byte #4: Attribute Table Entry to use for the following
Skip-Line code or characters
Byte #5: First display character, SL parameter, EOL or
EOS control code
Byte #6: Second display character, SL parameter, EOL or
EOS control code
Byte #7: Third display character, SL parameter, EOL or
EOS control code
Byte #n: Last display character in this color sequence, SL
parameter, EOL or EOS control code to use the
associated Attribute Table Entry.
TABLE 18. Sequence of Transmitted Bytes
This communication protocol is known as the Auto Attribute
Mode, which is also used by the LM1237 and LM1247.
Please see examples of usage for this mode in the LM1247
datasheet.
ENHANCED PAGE RAM ADDRESS MODES
Since the LM1246 is able to support 9-bit character codes, usually two bytes of Page RAM information has to be sent to every
location. To avoid this, the LM1246 addressing control system has 3 additional addressing modes offering increased flexibility that
may be helpful in sending data to the Page RAM. Some of the left over bits in the Attribute byte are employed as data control bits
to select the desired addressing mode as shown in Table 19. Attribute Byte. This is identified as the first byte sent in a write
operation or the Page RAM’s upper byte read in Table 7. Page RAM Upper Byte Read Data.
TABLE 19. Attribute Byte
ATTRIBUTE Byte
X DC[1] DC[0] CC[8]
ATT[3:0]
AUTO ATTRIBUTE MODE
The Auto Attribute mode is the standard LM1247 mode that is described above in the WRITING TO THE PAGE RAM section. The
attribute byte is shown in Table 20. Auto Attribute Mode.
TABLE 20. Auto Attribute Mode
ATTRIBUTE Byte
X
0
0
0
ATT[3:0]
When bits 6–5 are 0, the 9th character code and the 4-bit attribute code will be automatically applied to all the character codes
transmitted after this attribute byte, as in the LM1237 and LM1247. This mode is useful for sending character codes that use the
same attribute, and which are in the same 4 out of 8 banks of the Page ROM. A new transmission must be started to access
another character that is not in the same 4 banks of the Page ROM, and no further attribute codes can follow without stopping
and restarting a new transmission. The Page RAM address is automatically incremented starting with the initial LSB and MSB
address in the beginning of the sequence.
TWO BYTE COMMUNICATION MODE
The Two Byte Communication mode allows different attribute and character codes to be sent within one transmission without
stopping. The entire 512-character Page ROM is also fully accessible in this mode, without the need to stop and restart
transmission. The attribute byte is shown in Table 21. Two Byte Communication Mode, and the sequence of transmitted bytes is
shown in Table 22. Sequence of Transmitted Bytes. Either another attribute & character code pair or a STOP must follow after
each character code. The Page RAM address is automatically incremented just as in the Auto Attribute mode above.
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