LM1276 National Semiconductor Corporation, LM1276 Datasheet - Page 31

• Manufacturer Part Number: LM1276
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 512 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

Building Display Pages
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 LM1276 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 LM1276 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 6. This is identified as the first byte sent in a write operation or the Page
RAM’s upper byte read in Table 7.
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 16.
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 17, and the sequence of transmitted bytes is shown in Table 18. 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.
HALF RANDOM ADDRESS MODE
The Half Random Address mode allows different attribute and character codes to be sent within one transmission in the same
way as the Two Byte Communication mode. The entire 512-character Page ROM is fully accessible in this mode, without the need
to stop and restart transmission. The advantage of Half Random Addressing over the Two Byte mode is that the Page RAM
addresses do not have to be written to in a sequential order. However, the Page RAM addresses cannot be entirely random, as
they must be within one half of the Page RAM. A new transmission must be restarted to switch to another half of the Page RAM.
X
X
X
DC[1]
0
TABLE 17. Two Byte Communication Mode
0
TABLE 14. Sequence of Transmitted Bytes
TABLE 18. Sequence of Transmitted Bytes
(Continued)
TABLE 16. Auto Attribute Mode
DC[0]
0
1
TABLE 15. Attribute Byte
ATTRIBUTE Byte
ATTRIBUTE Byte
ATTRIBUTE Byte
CC[8]
CC[8]
0
31
ATT[3:0]
ATT[3:0]
ATT[3:0]
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