CAT5409WI-25 datasheet(6/16 Pages) CATALYST

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CAT5409

Doc. No. MD-2010 Rev. K

Characteristics subject to change without notice

SERIAL BUS PROTOCOL

The following defines the features of the I²C bus

protocol:

(1) Data transfer may be initiated only when the bus

is not busy.

(2) During a data transfer, the data line must remain

stable whenever the clock line is high. Any

changes in the data line while the clock is high will

be interpreted as a START or STOP condition.

The device controlling the transfer is a master,

typically a processor or controller, and the device

being controlled is the slave. The master will always

initiate data transfers and provide the clock for both

transmit and receive operations. Therefore, the

CAT5409 will be considered a slave device in all

applications.

START Condition

The START Condition precedes all commands to the

device, and is defined as a HIGH to LOW transition of

SDA when SCL is HIGH. The CAT5409 monitors the

SDA and SCL lines and will not respond until this

condition is met.

STOP Condition

A LOW to HIGH transition of SDA when SCL is HIGH

determines the STOP condition. All operations must

end with a STOP condition.

DEVICE ADDRESSING

The bus Master begins a transmission by sending a

START condition. The Master then sends the address

of the particular slave device it is requesting. The four

most significant bits of the 8-bit slave address are

fixed as 0101 for the CAT5409 (see Figure 5). The

next four significant bits (A3, A2, A1, A0) are the

device address bits and define which device the

Master is accessing. Up to sixteen devices may be

individually addressed by the system. Typically, +5V

and ground are hard-wired to these pins to establish

the device's address.

After the Master sends a START condition and the

slave address byte, the CAT5409 monitors the bus

and responds with an acknowledge (on the SDA line)

when its address matches the transmitted slave

address.

Acknowledge

After a successful data transfer, each receiving device

is required to generate an acknowledge. The

Acknowledging device pulls down the SDA line during

the ninth clock cycle, signaling that it received the 8

bits of data.

The CAT5409 responds with an acknowledge after

receiving a START condition and its slave address. If

the device has been selected along with a write

operation, it responds with an acknowledge after

receiving each 8-bit byte.

When the CAT5409 is in a READ mode it transmits 8

bits of data, releases the SDA line, and monitors the

line for an acknowledge. Once it receives this

acknowledge, the CAT5409 will continue to transmit

data. If no acknowledge is sent by the Master, the

device terminates data transmission and waits for a

STOP condition.

Figure 4. Acknowledge Timing

ACKNOWLEDGE

START

SCL FROM

MASTER

DATA OUTPUT

FROM TRANSMITTER

DATA OUTPUT

FROM RECEIVER

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