LM1236 National Semiconductor Corporation, LM1236 Datasheet - Page 24

• Manufacturer Part Number: LM1236
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

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OSD Generator Operation
Microcontroller Interface
The microcontroller interfaces to the LM1236 preamp using
the I
begins with a Start Pulse followed by a byte comprised of a
7-bit Slave Device Address and a Read/Write bit. Since the
first byte is composed of both the address and the read/write
bit, the address of the LM1236 for writing is 0xBA
(10111010b) and the address for reading is 0xBB
(10111011b). The development software provided by Na-
tional Semiconductor will automatically take care of the dif-
ference between the read and write addresses if the target
address under the communications tab is set to 0xBA. Fig-
ures 23, 24 show a write and read sequence on the I
compatible interface.
WRITE SEQUENCE
The write sequence begins with a start condition, which
consists of the master pulling SDA low while SCL is held
high. The Slave Device Write Address, 0xBA, is sent next.
Each byte that is sent is followed by an acknowledge bit.
When SCL is high, the master will release the SDA line. The
slave must pull SDA low to acknowledge. The register to be
written to is next sent in two bytes, the least significant byte
being sent first. The master can then send the data, which
consists of one or more bytes. Each data byte is followed by
an acknowledge bit. If more than one data byte is sent, the
data will increment to the next address location. See Figure
23 .
2
C compatible interface. The protocol of the interface
(Continued)
FIGURE 22. Bordering
2
C
24
READ SEQUENCE
Read sequences are comprised of two I2C compatible trans-
fer sequences: The first is a write sequence that only trans-
fers the two byte address to be accessed. The second is a
read sequence that starts at the address transferred in the
previous address only write access and increments to the
next address upon every data byte read. This is shown in
Figure 24 . The write sequence consists of the Start Pulse,
the Slave Device Write Address (0xBA), and the Acknowl-
edge bit; the next byte is the least significant byte of the
address to be accessed, followed by its Acknowledge bit.
This is then followed by a byte containing the most signifi-
cant address byte, followed by its Acknowledge bit. Then a
Stop bit indicates the end of the address only write access.
Next the read data access will be performed beginning with
the Start Pulse, the Slave Device Read Address (0xBB), and
the Acknowledge bit. The next 8 bits will be the read data
driven out by the LM1236 preamp associated with the ad-
dress indicated by the two address bytes. Subsequent read
data bytes will correspond to the next increment address
locations. Data should only be read from the LM1236 when
both OSD windows and the Fade In/ Fade Out are disabled.
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