Power-On Reset

Power-On Reset Requirements

Ramp-Up

Re-Ramp-Up

Time to Re-Ramp

Time

Ramp-Down

TCA8418

At power on, the GPIOs (ROW0–7 and COL0–9) are configured as inputs with internal 100-k

Ω pullups enabled.

However, the system master can enable the GPIOs to function as inputs, outputs or as part of the keypad matrix.

GPIOs not used for keypad control can be used to support other control features in the application.

ROW7–ROW0 are configured as inputs in GPIO mode with a push-pull structure, at power-on. In keyscan mode,

each has an open-drain structure with a 100-k

Ω pullup resistor and is used as an input.

COL9–COL0 are configured as inputs in GPIO mode with a push-pull structure, at power on. In keyscan mode,

each has an open-drain structure and is used as an output.

The system master can reset the TCA8418E in the event of a timeout or other improper operation by asserting a

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

to VCC, if no active connection is used.

RESET pin causes the same reset/initialization to occur without depowering the part. The RESET pin can also be

used as a shutdown pin, if the phone is closed.

The open-drain interrupt (INT) output is used to indicate to the system master that an input state (GPI or ROWs)

has changed. INT can be connected to the interrupt input of a microcontroller. By sending an interrupt signal on

this line, the remote input can inform the microcontroller if there is incoming data on its ports without having to

The TCA8418E has key lock capability, which can trigger an interrupt at key presses and releases, if selected

operating voltage for a power-reset cycle.

In the event of a glitch or data corruption, TCA8418E can be reset to its default conditions by using the power-on

reset feature. Power-on reset requires that the device go through a power cycle to be completely reset. This

reset also happens when the device is powered on for the first time in an application.

The two types of power-on reset are shown in Figure 1 and Figure 2.

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