QST104 datasheet(18/45 Pages) STMICROELECTRONICS

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Device operating modes

QST104

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4.6.3

IRQ pin

The IRQ pin is an open drain output with an internal pull-up. It can be used to inform the

Master device about any change in the key status. The IRQ line is pulled low every time the

state of any of the enabled keys changes. This includes any change in the touch state of the

key, a faulty key or a new calibration of one or more keys. The reported changes may then

be accessed by the Master device by using the GET_KEY_STATE command.

To improve communication response time, this signal suspends Low Power mode until the

Master device has issued a communication with the QST device.

4.6.4

Communication packet

The communication between the Master device and the QST104 (Slave) consists of two

standard I2C frames.

The first frame is sent by the Master device using the QST104 device address with the write

bit set. The data bytes consist of the command byte which is eventually followed by the

parameters and a checksum byte.

The second one is sent by the Master device using the QST104 device address with the

write bit reset. The QST104 completes the frame with data according to the command

previously sent by the Master device. The device finishes the frame by sending a checksum

byte for communication integrity verification.

If the read frame is omitted, the command may not be taken into account.

To initiate the communicate with the QST104, the Master device must send the

GET_DEVICE_INFO command in order to unlock access to all the other commands.

Figure 5.

Optional LED schematic

Ai12570

GPOn

VUNREG

C (10 nF)

QST104 Datasheet(PDF) 18 Page - STMicroelectronics