TPS2383

SLUS559B − APRIL 2003 − REVISED JULY 2004

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FUNCTIONAL DESCRIPTION

feature simplifies, earth grounded, controller applications that require opto-isolators to keep the 48-V return of

the ethernet power system floating. For applications where opto-isolation is not required, the bi-directional

property of the SDA line can be restored by connecting SDA_I to SDA_O. The SCL line is a unidirectional input

only line as the TPS2383 is always accesses as a slave device and it never controls the bus.

Data transfers that require a data-flow reversal on the SDA line are four-byte operations. This occurs during a

TPS2383 port read access cycle where a slave address byte is sent, followed by a port/register address byte

write. A second slave address byte is sent followed by the data byte read using the port/register setup from the

second byte in the sequence.

Data write transfers to the TPS2383 do not require a data-flow reversal and as such only a three-byte operation

is required. The sequence in this case is to send a slave address byte, followed by a write of the port/register

address followed by a write of the data byte for the addressed port.

1.

Start sequence (S)

2.

Slave address field

3.

Read/write

4.

Acknowledge

5.

Port/register address or data field

6.

Acknowledge/not acknowledge

7.

Stop sequence (P)

and the internal POR timer has timed out.

Start/Stop

The high-to-low transition of SDA while SCL is high defines the start condition. The low-to-high transition of SDA

while SCL is high defines the stop condition. The master device initiates all start and stop conditions.

A first serial packet enclosed within start and stop bits, consists of a seven-bit address field, read/write bit, and

the acknowledge bit. The acknowledge bit is always generated by the device receiving the address or data field.

Five of the seven address bits are used by the TPS2383. The sixth and seventh bit is a placeholder for future

expansion. During a write operation to the TPS2383 from the master device, the data field is eight bits. During

a read operation where the TPS2383 is writing to the master device, the data field is also eight bits.