ADM1029 datasheet(8/48 Pages) AD

8 / 48 page

REV. 0

ADM1029

–8–

SCL

SDA

ACK. BY

ADM1029

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1029

ACK. BY

ADM1029

STOP BY

MASTER

FRAME 3

DATA BYTE

SCL (CONTINUED)

SDA (CONTINUED)

Figure 4a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

SCL

SDA

ACK. BY

ADM1029

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1029

Figure 4b. Writing to the Address Pointer Register Only

SCL

SDA

NO ACK.

BY MASTER

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1029

ACK. BY

ADM1029

Figure 4c. Reading Data from a Previously Selected Register

The serial bus protocol operates as follows:

1. The master initiates data transfer by establishing a START

condition, defined as a high-to-low transition on the serial

data line SDA, while the serial clock line SCL remains high.

This indicates that an address/data stream will follow. All

slave peripherals connected to the serial bus respond to the

START condition, and shift in the next eight bits, consisting

of a 7-bit address (MSB first) plus an R/

W bit, which deter-

mines the direction of the data transfer, i.e., whether data

will be written to or read from the slave device.

The peripheral whose address corresponds to the transmitted

address responds by pulling the data line low during the low

period before the ninth clock pulse, known as the Acknowl-

edge Bit. All other devices on the bus now remain idle while

the selected device waits for data to be read from or written

to it. If the R/

W bit is a 0, the master will write to the slave

device. If the R/

W bit is a 1 the master will read from the

slave device.

2. Data is sent over the serial bus in sequences of nine clock

pulses, eight bits of data followed by an acknowledge bit

from the slave device. Transitions on the data line must

occur during the low period of the clock signal and remain

stable during the high period, as a low-to-high transition

when the clock is high may be interpreted as a STOP signal.

The number of data bytes that can be transmitted over the

serial bus in a single READ or WRITE operation is limited

only by what the master and slave devices can handle.

3. When all data bytes have been read or written, stop condi-

tions are established. In WRITE mode, the master will pull

the data line high during the tenth clock pulse to assert a

STOP condition. In READ mode, the master device will

override the acknowledge bit by pulling the data line high

during the low period before the ninth clock pulse. This is

known as No Acknowledge. The master will then take the

data line low during the low period before the tenth clock

pulse, high during the tenth clock pulse to assert a STOP

condition.

Any number of bytes of data may be transferred over the serial

bus in one operation, but it is not possible to mix read and write

in one operation, because the type of operation is determined at

the beginning and cannot subsequently be changed without

starting a new operation.

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