MC34844AEPR2 datasheet(49/62 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34844A

FUNCTIONAL DEVICE OPERATION

I2C BUS SPECIFICATION

MC34844A

charge of controlling LED dimming and enabling the device

every time the PWM is active. For this configuration the EN

pin should be LOW.

I2C BUS SPECIFICATION

The 34844A is a unidirectional device that can only be written by an external control unit. Since the device is a 7 bit address

device (1110110), the control unit needs to follow a specific data transfer format which is shown in Table 26.

Figure 26. A Complete Data Transfer

For a complete data transfer, please use this format in the

following order:

1. START condition

2. 34844A device address and Write instruction (R/W = 0)

3. First data pack, it corresponds to the 34844A register

that needs to be written. (refer to Table 13)

4. Second data pack, it corresponds to the value that

should be written to that register. (refer to Table 13)

5. STOP condition

I2C variables description:

• START: this condition occurs when SDA changes from

HIGH to LOW while SCK is HIGH.

• ACKNOWLEDGE: The acknowledge clock pulse is

generated by the Master (Control Unit).

• The transmitter releases the SDA line (HIGH) during the

acknowledge clock pulse.The receiver (34844A) must pull

down the SDA line during this acknowledge pulse to

indicate that the data was correctly written.

• Bits in the first byte: The first seven bits of the first bite

make up the slave address. The eighth bit is the LSB (least

significant bit), which determines the direction of the

message (Write = 0)

For the 34844A device, when an address is sent, each of

the devices in a system compares the first seven bits after

the START condition with its address. If they match, the

device considers itself addressed by the control unit as a

slave-receiver.

• STOP: this condition occurs when SDA changes from

LOW to HIGH while SCK is HIGH

For more information about “I2C BUS SPECIFICATION”

please refer to the following link:

http://www.nxp.com/acrobat_download/literature/

9398/39340011.pdf

MC34844AEPR2 Datasheet(PDF) 49 Page - Freescale Semiconductor, Inc

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