ADG2108BCPZ-R2 datasheet(19/28 Pages) AD

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ADG2108

Rev. 0 | Page 19 of 28

SERIAL INTERFACE

The ADG2108 is controlled via an I2C-compatible serial bus.

The parts are connected to this bus as a slave device (no clock

is generated by the switch).

HIGH SPEED I2C INTERFACE

In addition to standard and full speed I2C, the ADG2108 also

supports the high speed (3.4 MHz) I2C interface. Only the -HS

models provide this added performance. See the Ordering

Guide for details.

SERIAL BUS ADDRESS

The ADG2108 has a 7-bit slave address. The four MSBs are

hard coded to 1110, and the three LSBs are determined by the

state of Pin A0, Pin A1, and Pin A2. By offering the facility to

hardware configure Pin A0, Pin A1, and Pin A2, up to eight

of these devices can be connected to a single serial bus.

The 2-wire serial bus protocol operates as follows:

The master initiates data transfer by establishing a start

condition, defined as when a high-to-low transition on

the SDA line occurs while SCL is high. This indicates

that an address/data stream follows. 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 that determines the direction

of the data transfer, that is, whether data is written to or

read from the slave device.

The peripheral whose address corresponds to the

transmitted address responds by pulling the SDA

line low during the ninth clock pulse, known as the

acknowledge bit. At this stage, all other devices on the

bus remain idle while the selected device waits for data

to be written to or read from its serial register. If the

R/W bit is 1 (high), the master reads from the slave

device. If the R/W bit is 0 (low), the master writes to

the slave device.

Data is transmitted over the serial bus in sequences of

nine clock pulses: eight data bits followed by an acknowl-

edge bit from the receiver of the data. Transitions on the

SDA line must occur during the low period of the clock

signal, SCL, and remain stable during the high period of

SCL because a low-to-high transition when the clock is

high can be interpreted as a stop signal.

When all data bits have been read or written, a stop

condition is established by the master. A stop condition

is defined as a low-to-high transition on the SDA line

while SCL is high. In write mode, the master pulls the

SDA line high during the 10th clock pulse to establish

a stop condition. In read mode, the master issues a no

acknowledge for the ninth clock pulse (that is, the SDA

line remains high). The master then brings the SDA line

low before the 10th clock pulse and then high during the

10th clock pulse to establish a stop condition.

Refer to Figure 33 and Figure 34 for a graphical explanation

of the serial data transfer protocol.

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