TCA8418EYFPR datasheet(21/51 Pages) TI2

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TCA8418E

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SCPS222C – MAY 2010 – REVISED OCTOBER 2015

Device Functional Modes (continued)

8.4.2.2 Active Key Scan Mode

When the TCA8418E is in idle key scan mode, the device awaits a key press. Once a key is pressed in the

array, a low signal on one of the ROW pin inputs triggers an interrupt, which will turn on the internal oscillator

and enter the active key scan mode. At this point, the TCA8418E will start the key scan algorithm to determine

which key is being pressed, and/or it will use the internal oscillator for debouncing. Once all keys have been

released, the device will enter idle key scan mode.

8.5 Programming

8.5.1 I2C Interface

The TCA8418E has a standard bidirectional I2C interface that is controlled by a master device in order to be

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

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

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

internal register maps of the slave, 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 pullup resistor. The size of the pullup resistor is determined by the amount

of capacitance on the I2C lines. (For further details, refer to I2C pullup 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 master to access a slave device:

1. If a master wants to send data to a slave:

–

Master-transmitter sends a START condition and addresses the slave-receiver.

–

Master-transmitter sends data to slave-receiver.

–

Master-transmitter terminates the transfer with a STOP condition.

2. If a master wants to receive or read data from a slave:

–

Master-receiver sends a START condition and addresses the slave-transmitter.

–

Master-receiver sends the requested register to read to slave-transmitter.

–

Master-receiver receives data from the slave-transmitter.

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