LM1237AAFSLASHNA datasheet(19/42 Pages) NSC

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OSD Generator Operation (Continued)

Microcontroller Interface

The microcontroller interfaces to the LM1237 preamp via the

2C compatible interface. The protocol of the interface begins

with a Start Pulse followed by a byte comprised of a seven

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 LM1237 for writing is 0xBA

(10111010b)

and

the

address

for

reading

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-

ure 19 and Figure 20 show a write and read sequence on the

2C 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 address is next sent. The address

byte is made up of an address of seven bits (7-1) and the

read/write bit (0). Bit 0 is low to indicate a write operation.

Each byte that is sent is followed by an acknowledge. 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 19.

20023453

FIGURE 17. Shadowing

20023425

FIGURE 18. Bordering

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