ADM1029ARQZ-R7 datasheet(8/50 Pages) ONSEMI

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Table I. Resistor Ratios for Setting Serial Bus Address

3 MSBs

Ideal Ratio

Actual

Error

of ADC

R2/(R1 + R2)

(k )

R2/(R1 + R2)

Address

111

N/A

∞

0101111

110

0.8125

0.82

+0.75

0101110

101

0.6875

0.6812

–0.63

0101101

100

0.5625

0.5556

–0.69

0101100

011

0.4375

0.4444

+0.69

0101011

010

0.3125

0.3188

+0.63

0101010

001

0.1875

0.18

–0.75

0101001

000

N/A

∞

0101000

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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