TCA7408

SCPS235

– NOVEMBER 2011

www.ti.com

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

DESCRIPTION (CONTINUED)

At power on, the I/Os are configured as inputs. However, the system master can enable the I/Os as either inputs

or outputs by writing to the I/O direction bits. The data for each input or output is kept in the corresponding Input

or Output Register. All registers can be read by the system master.

The system master can reset the TCA7408 in the event of a timeout or other improper operation by asserting a

low in the RESET input. The power-on reset (POR) puts the registers in their default state and initializes the

part. The system master can also execute a software reset by asserting B0 in register 01h. The POR, and

hardware reset events will reset the state machine and the registers to the default state. A software reset will

only reset the registers to the default state and will not reset the state machine. In addition the watch dog timer

only resets the state machine

The TCA7408 open-drain interrupt (INT) output is activated when any GPIO set as an input has a transition to

the state opposite of that in the Input Default State (09h) register and the corresponding bit in the Interrupt Mask

Register (11h) is set to 0. It is used to indicate to the system master that an input has changed to a

pre-determined state. INT is also activated after either a hardware reset or software reset. Watch dog timer does

not activate the INT pin.

INT can be connected to the interrupt input of a microcontroller. By sending an interrupt signal on this line, the

remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via

200 ms (nominal). This reset does not reset the registers as they retain their previous value.

ORDERABLE PART NUMBER

TOP-SIDE MARKING

–40°C to 85°C

µCSP – ZSZ package

Tape and reel

TCA7408ZSZR

ZUQ

(1)

For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI

web site at www.ti.com.

(2)

Package drawings, thermal data, and symbolization are available at www.ti.com/packaging.

2

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© 2011, Texas Instruments Incorporated

Product Folder Link(s) :TCA7408