TCA6408ARSVR datasheet(21/50 Pages) TI2

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I2C/SMBus state machine are changed to their default state once RESET is low (0). When RESET is high (1),

the I/O levels at the P-port can be changed externally or through the controller. This input requires a pull-up

resistor to VCCI, if no active connection is used.

8.4 Device Functional Modes

8.4.1 Power-On Reset (POR)

When power (from 0 V) is applied to VCCP, an internal power-on reset holds the TCA6408A in a reset condition

until VCCP has reached VPOR. At that time, the reset condition is released, and the TCA6408A registers and

I2C/SMBus state machine initialize to their default states. After that, VCCP must be lowered to below VPORF and

back up to the operating voltage for a power-reset cycle.

8.4.2 Powered-Up

When power has been applied to both VCCP and VCCI and a POR has taken place, the device is in a functioning

mode. The device will always be ready to receive new requests via the I2C bus.

8.5 Programming

8.5.1 I2C Interface

The TCA6408A has a standard bidirectional I2C interface that is controlled by a controller device in order to

be configured or read the status of this device. Each target on the I2C bus has a specific device address

to differentiate between other target devices that are on the same I2C bus. Many target devices will require

configuration upon startup to set the behavior of the device. This is typically done when the controller accesses

internal register maps of the target, which have unique register addresses. A device can have one or multiple

registers where data is stored, written, or read.

The physical I2C interface consists of the serial clock (SCL) and serial data (SDA) lines. Both SDA and SCL lines

must be connected to VCC through a pull-up resistor. The size of the pull-up resistor is determined by the amount

of capacitance on the I2C lines. (For further details, refer to I2C Pull-up Resistor Calculation (SLVA689).) Data

transfer may be initiated only when the bus is idle. A bus is considered idle if both SDA and SCL lines are high

after a STOP condition.

The following is the general procedure for a controller to access a target device:

1. If a controller wants to send data to a target:

• Controller-transmitter sends a START condition and addresses the target-receiver.

• Controller-transmitter sends data to target-receiver.

• Controller-transmitter terminates the transfer with a STOP condition.

2. If a controller wants to receive or read data from a target:

• Controller-receiver sends a START condition and addresses the target-transmitter.

• Controller-receiver sends the requested register to read to target-transmitter.

• Controller-receiver receives data from the target-transmitter.

• Controller-receiver terminates the transfer with a STOP condition.

SCL

SDA

STAR T

Condition

STOP

Condition

Data Transfer

Figure 8-3. Definition of Start and Stop Conditions

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TCA6408A

SCPS192E – APRIL 2009 – REVISED JANUARY 2023

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