TCA8418E_15 Datasheet, PDF (21/50 Pages) Texas Instruments – I2C Controlled Keypad Scan IC With Integrated ESD Protection

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TCA8418E
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 V_CC 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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